Intx2MeshOnSphere.cpp

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/*
 * Intx2MeshOnSphere.cpp
 *
 *  Created on: Oct 3, 2012
 */
 
#ifdef _MSC_VER            /* windows */
#define _USE_MATH_DEFINES  // For M_PI
#endif
 
#include "moab/IntxMesh/Intx2MeshOnSphere.hpp"
#include "moab/IntxMesh/IntxUtils.hpp"
#include "moab/GeomUtil.hpp"
#include "moab/BoundBox.hpp"
#include "moab/MeshTopoUtil.hpp"
#ifdef MOAB_HAVE_MPI
#include "moab/ParallelComm.hpp"
#endif
#include "MBTagConventions.hpp"
 
#include <cassert>
 
// #define ENABLE_DEBUG
#define CHECK_CONVEXITY
namespace moab
{
 
Intx2MeshOnSphere::Intx2MeshOnSphere( Interface* mbimpl, IntxAreaUtils::AreaMethod amethod )
    : Intx2Mesh( mbimpl ), areaMethod( amethod ), plane( 0 ), Rsrc( 0.0 ), Rdest( 0.0 )
{
}
 
Intx2MeshOnSphere::~Intx2MeshOnSphere() {}
 
/*
 * return also the area for robustness verification
 */
double Intx2MeshOnSphere::setup_tgt_cell( EntityHandle tgt, int& nsTgt )
{
 
    // get coordinates of the target quad, to decide the gnomonic plane
    double cellArea = 0;
 
    int num_nodes;
    ErrorCode rval = mb->get_connectivity( tgt, tgtConn, num_nodes );MB_CHK_ERR_RET_VAL( rval, cellArea );
 
    nsTgt = num_nodes;
    // account for possible padded polygons
    while( tgtConn[nsTgt - 2] == tgtConn[nsTgt - 1] && nsTgt > 3 )
        nsTgt--;
 
    // CartVect coords[4];
    rval = mb->get_coords( tgtConn, nsTgt, &( tgtCoords[0][0] ) );MB_CHK_ERR_RET_VAL( rval, cellArea );
 
    CartVect middle = tgtCoords[0];
    for( int i = 1; i < nsTgt; i++ )
        middle += tgtCoords[i];
    middle = 1. / nsTgt * middle;
 
    IntxUtils::decide_gnomonic_plane( middle, plane );  // output the plane
    for( int j = 0; j < nsTgt; j++ )
    {
        // populate coords in the plane for intersection
        // they should be oriented correctly, positively
        rval = IntxUtils::gnomonic_projection( tgtCoords[j], Rdest, plane, tgtCoords2D[2 * j], tgtCoords2D[2 * j + 1] );MB_CHK_ERR_RET_VAL( rval, cellArea );
    }
 
    for( int j = 1; j < nsTgt - 1; j++ )
        cellArea += IntxUtils::area2D( &tgtCoords2D[0], &tgtCoords2D[2 * j], &tgtCoords2D[2 * j + 2] );
 
    // take target coords in order and compute area in plane
    return cellArea;
}
 
/* the elements are convex for sure, then do a gnomonic projection of both,
 *  compute intersection in the plane, then go back to the sphere for the points
 *  */
ErrorCode Intx2MeshOnSphere::computeIntersectionBetweenTgtAndSrc( EntityHandle tgt,
                                                                  EntityHandle src,
                                                                  double* P,
                                                                  int& nP,
                                                                  double& area,
                                                                  int markb[MAXEDGES],
                                                                  int markr[MAXEDGES],
                                                                  int& nsBlue,
                                                                  int& nsTgt,
                                                                  bool check_boxes_first )
{
    // the area will be used from now on, to see how well we fill the target cell with polygons
    // the points will be at most 40; they will describe a convex patch, after the points will be
    // ordered and collapsed (eliminate doubles)
 
    // CartVect srccoords[4];
    int num_nodes  = 0;
    ErrorCode rval = mb->get_connectivity( src, srcConn, num_nodes );MB_CHK_ERR( rval );
    nsBlue = num_nodes;
    // account for possible padded polygons
    while( srcConn[nsBlue - 2] == srcConn[nsBlue - 1] && nsBlue > 3 )
        nsBlue--;
    rval = mb->get_coords( srcConn, nsBlue, &( srcCoords[0][0] ) );MB_CHK_ERR( rval );
 
    area = 0.;
    nP   = 0;  // number of intersection points we are marking the boundary of src!
    if( check_boxes_first )
    {
        // look at the boxes formed with vertices; if they are far away, return false early
        // make sure the target is setup already
        setup_tgt_cell( tgt, nsTgt );  // we do not need area here
        // use here gnomonic plane (plane) to see where source is
        bool overlap3d = GeomUtil::bounding_boxes_overlap( tgtCoords, nsTgt, srcCoords, nsBlue, box_error );
        int planeb;
        CartVect mid3 = ( srcCoords[0] + srcCoords[1] + srcCoords[2] ) / 3;
        IntxUtils::decide_gnomonic_plane( mid3, planeb );
        if( !overlap3d && ( plane != planeb ) )  // plane was set at setup_tgt_cell
            return MB_SUCCESS;                   // no error, but no intersection, decide early to get out
        // if same plane, still check for gnomonic plane in 2d
        // if no overlap in 2d, get out
        if( !overlap3d && plane == planeb )  // CHECK 2D too
        {
            for( int j = 0; j < nsBlue; j++ )
            {
                rval = IntxUtils::gnomonic_projection( srcCoords[j], Rsrc, plane, srcCoords2D[2 * j],
                                                       srcCoords2D[2 * j + 1] );MB_CHK_ERR( rval );
            }
            bool overlap2d = GeomUtil::bounding_boxes_overlap_2d( srcCoords2D, nsBlue, tgtCoords2D, nsTgt, box_error );
            if( !overlap2d ) return MB_SUCCESS;  // we are sure they are not overlapping in 2d , either
        }
    }
#ifdef ENABLE_DEBUG
    if( dbg_1 )
    {
        std::cout << "tgt " << mb->id_from_handle( tgt ) << "\n";
        for( int j = 0; j < nsTgt; j++ )
        {
            std::cout << tgtCoords[j] << "\n";
        }
        std::cout << "src " << mb->id_from_handle( src ) << "\n";
        for( int j = 0; j < nsBlue; j++ )
        {
            std::cout << srcCoords[j] << "\n";
        }
        mb->list_entities( &tgt, 1 );
        mb->list_entities( &src, 1 );
    }
#endif
 
    for( int j = 0; j < nsBlue; j++ )
    {
        rval = IntxUtils::gnomonic_projection( srcCoords[j], Rsrc, plane, srcCoords2D[2 * j], srcCoords2D[2 * j + 1] );MB_CHK_ERR( rval );
    }
 
#ifdef ENABLE_DEBUG
    if( dbg_1 )
    {
        std::cout << "gnomonic plane: " << plane << "\n";
        std::cout << " target                                src\n";
        for( int j = 0; j < nsTgt; j++ )
        {
            std::cout << tgtCoords2D[2 * j] << " " << tgtCoords2D[2 * j + 1] << "\n";
        }
        for( int j = 0; j < nsBlue; j++ )
        {
            std::cout << srcCoords2D[2 * j] << " " << srcCoords2D[2 * j + 1] << "\n";
        }
    }
#endif
 
    rval = IntxUtils::EdgeIntersections2( srcCoords2D, nsBlue, tgtCoords2D, nsTgt, markb, markr, P, nP );MB_CHK_ERR( rval );
 
    int side[MAXEDGES] = { 0 };  // this refers to what side? source or tgt?
    int extraPoints =
        IntxUtils::borderPointsOfXinY2( srcCoords2D, nsBlue, tgtCoords2D, nsTgt, &( P[2 * nP] ), side, epsilon_area );
    if( extraPoints >= 1 )
    {
        for( int k = 0; k < nsBlue; k++ )
        {
            if( side[k] )
            {
                // this means that vertex k of source is inside convex tgt; mark edges k-1 and k in
                // src,
                //   as being "intersected" by tgt; (even though they might not be intersected by
                //   other edges, the fact that their apex is inside, is good enough)
                markb[k] = 1;
                markb[( k + nsBlue - 1 ) % nsBlue] =
                    1;  // it is the previous edge, actually, but instead of doing -1, it is
                // better to do modulo +3 (modulo 4)
                // null side b for next call
                side[k] = 0;
            }
        }
    }
    nP += extraPoints;
 
    extraPoints =
        IntxUtils::borderPointsOfXinY2( tgtCoords2D, nsTgt, srcCoords2D, nsBlue, &( P[2 * nP] ), side, epsilon_area );
    if( extraPoints >= 1 )
    {
        for( int k = 0; k < nsTgt; k++ )
        {
            if( side[k] )
            {
                // this is to mark that target edges k-1 and k are intersecting src
                markr[k] = 1;
                markr[( k + nsTgt - 1 ) % nsTgt] =
                    1;  // it is the previous edge, actually, but instead of doing -1, it is
                // better to do modulo +3 (modulo 4)
                // null side b for next call
            }
        }
    }
    nP += extraPoints;
 
    // now sort and orient the points in P, such that they are forming a convex polygon
    // this will be the foundation of our new mesh
    // this works if the polygons are convex
    IntxUtils::SortAndRemoveDoubles2( P, nP, epsilon_1 );  // nP should be at most 8 in the end ?
    // if there are more than 3 points, some area will be positive
 
    if( nP >= 3 )
    {
        for( int k = 1; k < nP - 1; k++ )
            area += IntxUtils::area2D( P, &P[2 * k], &P[2 * k + 2] );
#ifdef CHECK_CONVEXITY
        // each edge should be large enough that we can compute angles between edges
        for( int k = 0; k < nP; k++ )
        {
            int k1              = ( k + 1 ) % nP;
            int k2              = ( k1 + 1 ) % nP;
            double orientedArea = IntxUtils::area2D( &P[2 * k], &P[2 * k1], &P[2 * k2] );
            if( orientedArea < 0 )
            {
                std::cout << " oriented area is negative: " << orientedArea << " k:" << k << " target, src:" << tgt
                          << " " << src << " \n";
            }
        }
#endif
    }
 
    return MB_SUCCESS;  // no error
}
 
// this method will also construct the triangles/quads/polygons in the new mesh
// if we accept planar polygons, we just save them
// also, we could just create new vertices every time, and merge only in the end;
// could be too expensive, and the tolerance for merging could be an
// interesting topic
ErrorCode Intx2MeshOnSphere::findNodes( EntityHandle tgt, int nsTgt, EntityHandle src, int nsBlue, double* iP, int nP )
{
#ifdef ENABLE_DEBUG
    // first of all, check against target and source vertices
    //
    if( dbg_1 )
    {
        std::cout << "tgt, src, nP, P " << mb->id_from_handle( tgt ) << " " << mb->id_from_handle( src ) << " " << nP
                  << "\n";
        for( int n = 0; n < nP; n++ )
            std::cout << " \t" << iP[2 * n] << "\t" << iP[2 * n + 1] << "\n";
    }
#endif
 
    // get the edges for the target triangle; the extra points will be on those edges, saved as
    // lists (unordered)
 
    // first get the list of edges adjacent to the target cell
    // use the neighTgtEdgeTag
    EntityHandle adjTgtEdges[MAXEDGES];
    ErrorCode rval = mb->tag_get_data( neighTgtEdgeTag, &tgt, 1, &( adjTgtEdges[0] ) );MB_CHK_SET_ERR( rval, "can't get edge target tag" );
    // we know that we have only nsTgt edges here; [nsTgt, MAXEDGES) are ignored, but it is small
    // potatoes some of them will be handles to the initial vertices from source or target meshes
 
    std::vector< EntityHandle > foundIds;
    foundIds.resize( nP );
#ifdef CHECK_CONVEXITY
    int npBefore1 = nP;
    int oldNodes  = 0;
    int otherIntx = 0;
    moab::IntxAreaUtils areaAdaptor;
#endif
    for( int i = 0; i < nP; i++ )
    {
        double* pp = &iP[2 * i];  // iP+2*i
        // project the point back on the sphere
        CartVect pos;
        IntxUtils::reverse_gnomonic_projection( pp[0], pp[1], Rdest, plane, pos );
        int found = 0;
        // first, are they on vertices from target or src?
        // priority is the target mesh (mb2?)
        int j                = 0;
        EntityHandle outNode = (EntityHandle)0;
        for( j = 0; j < nsTgt && !found; j++ )
        {
            // int node = tgtTri.v[j];
            double d2 = IntxUtils::dist2( pp, &tgtCoords2D[2 * j] );
            if( d2 < epsilon_1 / 1000 ) // two orders of magnitude smaller than it should, to avoid concave polygons
            {
 
                foundIds[i] = tgtConn[j];  // no new node
                found       = 1;
#ifdef CHECK_CONVEXITY
                oldNodes++;
#endif
#ifdef ENABLE_DEBUG
                if( dbg_1 )
                    std::cout << "  target node j:" << j << " id:" << mb->id_from_handle( tgtConn[j] )
                              << " 2d coords:" << tgtCoords2D[2 * j] << "  " << tgtCoords2D[2 * j + 1] << " d2: " << d2
                              << " \n";
#endif
            }
        }
 
        for( j = 0; j < nsBlue && !found; j++ )
        {
            // int node = srcTri.v[j];
            double d2 = IntxUtils::dist2( pp, &srcCoords2D[2 * j] );
            if( d2 < epsilon_1 / 1000 )
            {
                // suspect is srcConn[j] corresponding in mbOut
 
                foundIds[i] = srcConn[j];  // no new node
                found       = 1;
#ifdef CHECK_CONVEXITY
                oldNodes++;
#endif
#ifdef ENABLE_DEBUG
                if( dbg_1 )
                    std::cout << "  source node " << j << " " << mb->id_from_handle( srcConn[j] ) << " d2:" << d2
                              << " \n";
#endif
            }
        }
 
        if( !found )
        {
            // find the edge it belongs, first, on the red element
            // look at the minimum area, not at the first below some tolerance
            double minArea = 1.e+38;
            int index_min  = -1;
            for( j = 0; j < nsTgt; j++ )
            {
                int j1      = ( j + 1 ) % nsTgt;
                double area = fabs( IntxUtils::area2D( &tgtCoords2D[2 * j], &tgtCoords2D[2 * j1], pp ) );
                // how to check if pp is between redCoords2D[j] and redCoords2D[j1] ?
                // they should form a straight line; the sign should be -1
                double checkx = IntxUtils::dist2( &tgtCoords2D[2 * j], pp ) +
                                IntxUtils::dist2( &tgtCoords2D[2 * j1], pp ) -
                                IntxUtils::dist2( &tgtCoords2D[2 * j], &tgtCoords2D[2 * j1] );
                if( area < minArea && checkx < 2 * epsilon_1 )  // round off error or not?
                {
                    index_min = j;
                    minArea   = area;
                }
            }
            // verify that index_min is valid
            assert( index_min >= 0 );
 
            if( minArea < epsilon_1 / 2 )  // we found the smallest area, so we think we found the
                                           // target edge it belongs
            {
                // found the edge; now find if there is a point in the list here
                // std::vector<EntityHandle> * expts = extraNodesMap[tgtEdges[j]];
                int indx = TgtEdges.index( adjTgtEdges[index_min] );
                if( indx < 0 )  // CID 181166 (#1 of 1): Argument cannot be negative (NEGATIVE_RETURNS)
                {
                    std::cerr << " error in adjacent target edge: " << mb->id_from_handle( adjTgtEdges[index_min] )
                              << "\n";
                    return MB_FAILURE;
                }
                std::vector< EntityHandle >* expts = extraNodesVec[indx];
                // if the points pp is between extra points, then just give that id
                // if not, create a new point, (check the id)
                // get the coordinates of the extra points so far
                int nbExtraNodesSoFar = expts->size();
                if( nbExtraNodesSoFar > 0 )
                {
                    std::vector< CartVect > coords1;
                    coords1.resize( nbExtraNodesSoFar );
                    mb->get_coords( &( *expts )[0], nbExtraNodesSoFar, &( coords1[0][0] ) );
                    // std::list<int>::iterator it;
                    for( int k = 0; k < nbExtraNodesSoFar && !found; k++ )
                    {
                        // int pnt = *it;
                        double d2 = ( pos - coords1[k] ).length();
                        if( d2 < 2 * epsilon_1 )  // is this below machine precision?
                        {
                            found       = 1;
                            foundIds[i] = ( *expts )[k];
#ifdef CHECK_CONVEXITY
                            otherIntx++;
#endif
                        }
                    }
                }
                if( !found )
                {
                    // create a new point in 2d (at the intersection)
                    // foundIds[i] = m_num2dPoints;
                    // expts.push_back(m_num2dPoints);
                    // need to create a new node in mbOut
                    // this will be on the edge, and it will be added to the local list
                    rval = mb->create_vertex( pos.array(), outNode );MB_CHK_ERR( rval );
                    ( *expts ).push_back( outNode );
                    // CID 181168; avoid leak storage error
                    rval = mb->add_entities( outSet, &outNode, 1 );MB_CHK_ERR( rval );
                    foundIds[i] = outNode;
                    found       = 1;
                }
            }
        }
        if( !found )
        {
            std::cout << " target quad: ";
            for( int j1 = 0; j1 < nsTgt; j1++ )
            {
                std::cout << tgtCoords2D[2 * j1] << " " << tgtCoords2D[2 * j1 + 1] << "\n";
            }
            std::cout << " a point pp is not on a target quad " << *pp << " " << pp[1] << " target quad "
                      << mb->id_from_handle( tgt ) << " \n";
            return MB_FAILURE;
        }
    }
#ifdef ENABLE_DEBUG
    if( dbg_1 )
    {
        std::cout << " candidate polygon: nP" << nP << " plane: " << plane << "\n";
        for( int i1 = 0; i1 < nP; i1++ )
            std::cout << iP[2 * i1] << " " << iP[2 * i1 + 1] << " " << foundIds[i1] << "\n";
    }
#endif
    // first, find out if we have nodes collapsed; shrink them
    // we may have to reduce nP
    // it is possible that some nodes are collapsed after intersection only
    // nodes will always be in order (convex intersection)
#ifdef CHECK_CONVEXITY
    int npBefore2 = nP;
#endif
    correct_polygon( &foundIds[0], nP );
    // now we can build the triangles, from P array, with foundIds
    // we will put them in the out set
    if( nP >= 3 )
    {
        EntityHandle polyNew;
        rval = mb->create_element( MBPOLYGON, &foundIds[0], nP, polyNew );MB_CHK_ERR( rval );
        rval = mb->add_entities( outSet, &polyNew, 1 );MB_CHK_ERR( rval );
 
        // tag it with the global ids from target and source elements
        int globalID;
        rval = mb->tag_get_data( gid, &src, 1, &globalID );MB_CHK_ERR( rval );
        rval = mb->tag_set_data( srcParentTag, &polyNew, 1, &globalID );MB_CHK_ERR( rval );
        // if(!parcomm->rank()) std::cout << "Setting parent for " << mb->id_from_handle(polyNew) <<
        // " : Blue = " << globalID << ", " << mb->id_from_handle(src) << "\t\n";
        rval = mb->tag_get_data( gid, &tgt, 1, &globalID );MB_CHK_ERR( rval );
        rval = mb->tag_set_data( tgtParentTag, &polyNew, 1, &globalID );MB_CHK_ERR( rval );
        // if(parcomm->rank()) std::cout << "Setting parent for " << mb->id_from_handle(polyNew) <<
        // " : target = " << globalID << ", " << mb->id_from_handle(tgt) << "\n";
 
        counting++;
        rval = mb->tag_set_data( countTag, &polyNew, 1, &counting );MB_CHK_ERR( rval );
        if( orgSendProcTag )
        {
            int org_proc = -1;
            rval         = mb->tag_get_data( orgSendProcTag, &src, 1, &org_proc );MB_CHK_ERR( rval );
            rval = mb->tag_set_data( orgSendProcTag, &polyNew, 1, &org_proc );MB_CHK_ERR( rval );  // yet another tag
        }
#ifdef CHECK_CONVEXITY
        // each edge should be large enough that we can compute angles between edges
        std::vector< double > coords;
        coords.resize( 3 * nP );
        rval = mb->get_coords( &foundIds[0], nP, &coords[0] );MB_CHK_ERR( rval );
        std::vector< CartVect > posi( nP );
        rval = mb->get_coords( &foundIds[0], nP, &( posi[0][0] ) );MB_CHK_ERR( rval );
 
        for( int k = 0; k < nP; k++ )
        {
            int k1 = ( k + 1 ) % nP;
            int k2 = ( k1 + 1 ) % nP;
            double orientedArea = areaAdaptor. area_spherical_triangle( &coords[3 * k], &coords[3 * k1], &coords[3 * k2], Rdest );
            if( orientedArea < 0 )
            {
                std::cout << " np before 1 , 2, current " << npBefore1 << " " << npBefore2 << " " << nP << "\n";
                for( int i = 0; i < nP; i++ )
                {
                    int nexti         = ( i + 1 ) % nP;
                    double lengthEdge = ( posi[i] - posi[nexti] ).length();
                    std::cout << " " << foundIds[i] << " edge en:" << lengthEdge << "\n";
                }
                std::cout << " old verts: " << oldNodes << " other intx:" << otherIntx << "\n";
 
                std::cout << "rank:" << my_rank << " oriented area in 3d is negative: " << orientedArea << " k:" << k
                          << " target, src:" << tgt << " " << src << " \n";
            }
        }
#endif
 
#ifdef ENABLE_DEBUG
        if( dbg_1 )
        {
            std::cout << "Counting: " << counting << "\n";
            std::cout << " polygon " << mb->id_from_handle( polyNew ) << "  nodes: " << nP << " :";
            for( int i1 = 0; i1 < nP; i1++ )
                std::cout << " " << mb->id_from_handle( foundIds[i1] );
            std::cout << " plane: " << plane << "\n";
            std::vector< CartVect > posi( nP );
            mb->get_coords( &foundIds[0], nP, &( posi[0][0] ) );
            for( int i1 = 0; i1 < nP; i1++ )
                std::cout << foundIds[i1] << " " << posi[i1] << "\n";
 
            std::stringstream fff;
            fff << "file0" << counting << ".vtk";
            rval = mb->write_mesh( fff.str().c_str(), &outSet, 1 );MB_CHK_ERR( rval );
        }
#endif
    }
    // else {
    //   std::cout << "[[FAILURE]] Number of vertices in polygon is less than 3\n";
    // }
    // disable_debug();
    return MB_SUCCESS;
}
 
ErrorCode Intx2MeshOnSphere::update_tracer_data( EntityHandle out_set, Tag& tagElem, Tag& tagArea )
{
    EntityHandle dum = 0;
 
    Tag corrTag;
    ErrorCode rval = mb->tag_get_handle( CORRTAGNAME, 1, MB_TYPE_HANDLE, corrTag, MB_TAG_DENSE,
                                         &dum );  // it should have been created
    MB_CHK_SET_ERR( rval, "can't get correlation tag" );
 
    // get all polygons out of out_set; then see where are they coming from
    Range polys;
    rval = mb->get_entities_by_dimension( out_set, 2, polys );MB_CHK_SET_ERR( rval, "can't get polygons out" );
 
    // rs2 is the target range, arrival; rs1 is src, departure;
    // there is a connection between rs1 and rs2, through the corrTag
    // corrTag is __correlation
    // basically, mb->tag_get_data(corrTag, &(tgtPoly), 1, &srcPoly);
    // also,  mb->tag_get_data(corrTag, &(srcPoly), 1, &tgtPoly);
    // we start from rs2 existing, then we have to update something
 
    // tagElem will have multiple tracers
    int numTracers = 0;
    rval           = mb->tag_get_length( tagElem, numTracers );MB_CHK_SET_ERR( rval, "can't get number of tracers in simulation" );
    if( numTracers < 1 ) MB_CHK_SET_ERR( MB_FAILURE, "no tracers data" );
 
    std::vector< double > currentVals( rs2.size() * numTracers );
    rval = mb->tag_get_data( tagElem, rs2, &currentVals[0] );MB_CHK_SET_ERR( rval, "can't get existing tracers values" );
 
    // create new tuple list for tracers to other processors, from remote_cells
#ifdef MOAB_HAVE_MPI
    if( remote_cells )
    {
        int n = remote_cells->get_n();
        if( n > 0 )
        {
            remote_cells_with_tracers = new TupleList();
            remote_cells_with_tracers->initialize( 2, 0, 1, numTracers,
                                                   n );  // tracers are in these tuples
            remote_cells_with_tracers->enableWriteAccess();
            for( int i = 0; i < n; i++ )
            {
                remote_cells_with_tracers->vi_wr[2 * i]     = remote_cells->vi_wr[2 * i];
                remote_cells_with_tracers->vi_wr[2 * i + 1] = remote_cells->vi_wr[2 * i + 1];
                //    remote_cells->vr_wr[i] = 0.; will have a different tuple for communication
                remote_cells_with_tracers->vul_wr[i] =
                    remote_cells->vul_wr[i];  // this is the corresponding target cell (arrival)
                for( int k = 0; k < numTracers; k++ )
                    remote_cells_with_tracers->vr_wr[numTracers * i + k] = 0;  // initialize tracers to be transported
                remote_cells_with_tracers->inc_n();
            }
        }
        delete remote_cells;
        remote_cells = NULL;
    }
#endif
    // for each polygon, we have 2 indices: target and source parents
    // we need index source to update index tgt?
    std::vector< double > newValues( rs2.size() * numTracers,
                                     0. );  // initialize with 0 all of them
    // area of the polygon * conc on target (old) current quantity
    // finally, divide by the area of the tgt
    double check_intx_area = 0.;
    moab::IntxAreaUtils intxAreas( this->areaMethod );  // use_lHuiller = true
    for( Range::iterator it = polys.begin(); it != polys.end(); ++it )
    {
        EntityHandle poly = *it;
        int srcIndex, tgtIndex;
        rval = mb->tag_get_data( srcParentTag, &poly, 1, &srcIndex );MB_CHK_SET_ERR( rval, "can't get source tag" );
 
        EntityHandle src = rs1[srcIndex - 1];  // big assumption, it should work for meshes where global id is the same
        // as element handle (ordered from 1 to number of elements); should be OK for Homme meshes
        rval = mb->tag_get_data( tgtParentTag, &poly, 1, &tgtIndex );MB_CHK_SET_ERR( rval, "can't get target tag" );
        // EntityHandle target = rs2[tgtIndex];
        // big assumption here, target and source are "parallel" ;we should have an index from
        // source to target (so a deformed source corresponds to an arrival tgt)
        /// TODO: VSM: Its unclear whether we need the source or destination radius here.
        double radius = Rsrc;
        double areap  = intxAreas.area_spherical_element( mb, poly, radius );
        check_intx_area += areap;
        // so the departure cell at time t (srcIndex) covers a portion of a tgtCell
        // that quantity will be transported to the tgtCell at time t+dt
        // the source corresponds to a target arrival
        EntityHandle tgtArr;
        rval = mb->tag_get_data( corrTag, &src, 1, &tgtArr );
        if( 0 == tgtArr || MB_TAG_NOT_FOUND == rval )
        {
#ifdef MOAB_HAVE_MPI
            if( !remote_cells_with_tracers ) MB_CHK_SET_ERR( MB_FAILURE, "no remote cells, failure\n" );
            // maybe the element is remote, from another processor
            int global_id_src;
            rval = mb->tag_get_data( gid, &src, 1, &global_id_src );MB_CHK_SET_ERR( rval, "can't get arrival target for corresponding source gid" );
            // find the
            int index_in_remote = remote_cells_with_tracers->find( 1, global_id_src );
            if( index_in_remote == -1 )
                MB_CHK_SET_ERR( MB_FAILURE, "can't find the global id element in remote cells\n" );
            for( int k = 0; k < numTracers; k++ )
                remote_cells_with_tracers->vr_wr[index_in_remote * numTracers + k] +=
                    currentVals[numTracers * ( tgtIndex - 1 ) + k] * areap;
#endif
        }
        else if( MB_SUCCESS == rval )
        {
            int arrTgtIndex = rs2.index( tgtArr );
            if( -1 == arrTgtIndex ) MB_CHK_SET_ERR( MB_FAILURE, "can't find the target arrival index" );
            for( int k = 0; k < numTracers; k++ )
                newValues[numTracers * arrTgtIndex + k] += currentVals[( tgtIndex - 1 ) * numTracers + k] * areap;
        }
 
        else
            MB_CHK_SET_ERR( rval, "can't get arrival target for corresponding " );
    }
    // now, send back the remote_cells_with_tracers to the processors they came from, with the
    // updated values for the tracer mass in a cell
#ifdef MOAB_HAVE_MPI
    if( remote_cells_with_tracers )
    {
        // so this means that some cells will be sent back with tracer info to the procs they were
        // sent from
        ( parcomm->proc_config().crystal_router() )->gs_transfer( 1, *remote_cells_with_tracers, 0 );
        // now, look at the global id, find the proper "tgt" cell with that index and update its
        // mass
        // remote_cells->print("remote cells after routing");
        int n = remote_cells_with_tracers->get_n();
        for( int j = 0; j < n; j++ )
        {
            EntityHandle tgtCell = remote_cells_with_tracers->vul_rd[j];  // entity handle sent back
            int arrTgtIndex      = rs2.index( tgtCell );
            if( -1 == arrTgtIndex ) MB_CHK_SET_ERR( MB_FAILURE, "can't find the target arrival index" );
            for( int k = 0; k < numTracers; k++ )
                newValues[arrTgtIndex * numTracers + k] += remote_cells_with_tracers->vr_rd[j * numTracers + k];
        }
    }
#endif /* MOAB_HAVE_MPI */
    // now divide by target area (current)
    int j                = 0;
    Range::iterator iter = rs2.begin();
    void* data           = NULL;  // used for stored area
    int count            = 0;
    std::vector< double > total_mass_local( numTracers, 0. );
    while( iter != rs2.end() )
    {
        rval = mb->tag_iterate( tagArea, iter, rs2.end(), count, data );MB_CHK_SET_ERR( rval, "can't tag iterate" );
        double* ptrArea = (double*)data;
        for( int i = 0; i < count; i++, ++iter, j++, ptrArea++ )
        {
            for( int k = 0; k < numTracers; k++ )
            {
                total_mass_local[k] += newValues[j * numTracers + k];
                newValues[j * numTracers + k] /= ( *ptrArea );
            }
        }
    }
    rval = mb->tag_set_data( tagElem, rs2, &newValues[0] );MB_CHK_SET_ERR( rval, "can't set new values tag" );
 
#ifdef MOAB_HAVE_MPI
    std::vector< double > total_mass( numTracers, 0. );
    double total_intx_area = 0;
    int mpi_err =
        MPI_Reduce( &total_mass_local[0], &total_mass[0], numTracers, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD );
    if( MPI_SUCCESS != mpi_err ) return MB_FAILURE;
    // now reduce total area
    mpi_err = MPI_Reduce( &check_intx_area, &total_intx_area, 1, MPI_DOUBLE, MPI_SUM, 0, MPI_COMM_WORLD );
    if( MPI_SUCCESS != mpi_err ) return MB_FAILURE;
    if( my_rank == 0 )
    {
        for( int k = 0; k < numTracers; k++ )
            std::cout << "total mass now tracer k=" << k + 1 << " " << total_mass[k] << "\n";
        std::cout << "check: total intersection area: (4 * M_PI * R^2): " << 4 * M_PI * Rsrc * Rsrc << " "
                  << total_intx_area << "\n";
    }
 
    if( remote_cells_with_tracers )
    {
        delete remote_cells_with_tracers;
        remote_cells_with_tracers = NULL;
    }
#else
    for( int k = 0; k < numTracers; k++ )
        std::cout << "total mass now tracer k=" << k + 1 << " " << total_mass_local[k] << "\n";
    std::cout << "check: total intersection area: (4 * M_PI * R^2): " << 4 * M_PI * Rsrc * Rsrc << " "
              << check_intx_area << "\n";
#endif
    return MB_SUCCESS;
}
 
#ifdef MOAB_HAVE_MPI
ErrorCode Intx2MeshOnSphere::build_processor_euler_boxes( EntityHandle euler_set, Range& local_verts, bool gnomonic )
{
    if( !gnomonic )
    {
        return Intx2Mesh::build_processor_euler_boxes( euler_set, local_verts, gnomonic );
    }
    localEnts.clear();
    ErrorCode rval = mb->get_entities_by_dimension( euler_set, 2, localEnts );MB_CHK_SET_ERR( rval, "can't get local ents" );
 
    rval = mb->get_connectivity( localEnts, local_verts );MB_CHK_SET_ERR( rval, "can't get connectivity" );
    int num_local_verts = (int)local_verts.size();
 
    assert( parcomm != NULL );
 
    if( num_local_verts == 0 )
    {
        // it is probably point cloud, get the local vertices from set
        rval = mb->get_entities_by_dimension( euler_set, 0, local_verts );MB_CHK_SET_ERR( rval, "can't get local vertices from set" );
        num_local_verts = (int)local_verts.size();
        localEnts       = local_verts;
    }
    // will use 6 gnomonic planes to decide boxes for each gnomonic plane
    // each gnomonic box will be 2d, min, max
    double gnom_box[24];
    for( int i = 0; i < 6; i++ )
    {
        gnom_box[4 * i] = gnom_box[4 * i + 1] = DBL_MAX;
        gnom_box[4 * i + 2] = gnom_box[4 * i + 3] = -DBL_MAX;
    }
 
    // there are 6 gnomonic planes; some elements could be on the corners, and affect multiple
    // planes decide what gnomonic planes will be affected by each cell some elements could appear
    // in multiple gnomonic planes !
    std::vector< double > coords( 3 * num_local_verts );
    rval = mb->get_coords( local_verts, &coords[0] );MB_CHK_SET_ERR( rval, "can't get vertex coords" );ERRORR( rval, "can't get coords of vertices " );
    // decide each local vertex to what gnomonic plane it belongs
 
    std::vector< int > gnplane;
    gnplane.resize( num_local_verts );
    for( int i = 0; i < num_local_verts; i++ )
    {
        CartVect pos( &coords[3 * i] );
        int pl;
        IntxUtils::decide_gnomonic_plane( pos, pl );
        gnplane[i] = pl;
    }
 
    for( Range::iterator it = localEnts.begin(); it != localEnts.end(); it++ )
    {
        EntityHandle cell   = *it;
        EntityType typeCell = mb->type_from_handle( cell );  // could be vertex, for point cloud
        // get coordinates, and decide gnomonic planes for it
        int nnodes;
        const EntityHandle* conn = NULL;
        EntityHandle c[1];
        if( typeCell != MBVERTEX )
        {
            rval = mb->get_connectivity( cell, conn, nnodes );MB_CHK_SET_ERR( rval, "can't get connectivity" );
        }
        else
        {
            nnodes = 1;
            c[0]   = cell;  // actual node
            conn   = &c[0];
        }
        // get coordinates of vertices involved with this
        std::vector< double > elco( 3 * nnodes );
        std::set< int > planes;
        for( int i = 0; i < nnodes; i++ )
        {
            int ix = local_verts.index( conn[i] );
            planes.insert( gnplane[ix] );
            for( int j = 0; j < 3; j++ )
            {
                elco[3 * i + j] = coords[3 * ix + j];
            }
        }
        // now, augment the boxes for all planes involved
        for( std::set< int >::iterator st = planes.begin(); st != planes.end(); st++ )
        {
            int pl = *st;
            for( int i = 0; i < nnodes; i++ )
            {
                CartVect pos( &elco[3 * i] );
                double c2[2];
                IntxUtils::gnomonic_projection( pos, Rdest, pl, c2[0],
                                                c2[1] );  // 2 coordinates
                //
                for( int k = 0; k < 2; k++ )
                {
                    double val = c2[k];
                    if( val < gnom_box[4 * ( pl - 1 ) + k] ) gnom_box[4 * ( pl - 1 ) + k] = val;  // min in k direction
                    if( val > gnom_box[4 * ( pl - 1 ) + 2 + k] )
                        gnom_box[4 * ( pl - 1 ) + 2 + k] = val;  // max in k direction
                }
            }
        }
    }
 
    int numprocs = parcomm->proc_config().proc_size();
    allBoxes.resize( 24 * numprocs );  // 6 gnomonic planes , 4 doubles for each for 2d box
 
    my_rank = parcomm->proc_config().proc_rank();
    for( int k = 0; k < 24; k++ )
        allBoxes[24 * my_rank + k] = gnom_box[k];
 
    // now communicate to get all boxes
    int mpi_err;
#if( MPI_VERSION >= 2 )
    // use "in place" option
    mpi_err = MPI_Allgather( MPI_IN_PLACE, 0, MPI_DATATYPE_NULL, &allBoxes[0], 24, MPI_DOUBLE,
                             parcomm->proc_config().proc_comm() );
#else
    {
        std::vector< double > allBoxes_tmp( 24 * parcomm->proc_config().proc_size() );
        mpi_err  = MPI_Allgather( &allBoxes[24 * my_rank], 6, MPI_DOUBLE, &allBoxes_tmp[0], 24, MPI_DOUBLE,
                                  parcomm->proc_config().proc_comm() );
        allBoxes = allBoxes_tmp;
    }
#endif
    if( MPI_SUCCESS != mpi_err ) return MB_FAILURE;
 
#ifdef VERBOSE
    if( my_rank == 0 )
    {
        std::cout << " maximum number of vertices per cell are " << max_edges_1 << " on first mesh and " << max_edges_2
                  << " on second mesh \n";
        for( int i = 0; i < numprocs; i++ )
        {
            std::cout << "task: " << i << " \n";
            for( int pl = 1; pl <= 6; pl++ )
            {
                std::cout << "  plane " << pl << " min: \t" << allBoxes[24 * i + 4 * ( pl - 1 )] << " \t"
                          << allBoxes[24 * i + 4 * ( pl - 1 ) + 1] << "\n";
                std::cout << " \t  max: \t" << allBoxes[24 * i + 4 * ( pl - 1 ) + 2] << " \t"
                          << allBoxes[24 * i + 4 * ( pl - 1 ) + 3] << "\n";
            }
        }
    }
#endif
 
    return MB_SUCCESS;
}
//#define VERBOSE
// this will use the bounding boxes for the (euler)/ fix  mesh that are already established
// will distribute the mesh to other procs, so that on each task, the covering set covers the local
// bounding box this means it will cover the second (local) mesh set; So the covering set will cover
// completely the second local mesh set (in intersection)
ErrorCode Intx2MeshOnSphere::construct_covering_set( EntityHandle& initial_distributed_set,
                                                     EntityHandle& covering_set,
                                                     bool gnomonic,
                                                     int order )
{
    // primary element came from, in the joint communicator ; this will be forwarded by coverage
    // mesh needed for tag migrate later on
    int defaultInt = -1;  // no processor, so it was not migrated from somewhere else
    ErrorCode rval = mb->tag_get_handle( "orig_sending_processor", 1, MB_TYPE_INTEGER, orgSendProcTag,
                                         MB_TAG_DENSE | MB_TAG_CREAT, &defaultInt );MB_CHK_SET_ERR( rval, "can't create original sending processor tag" );
 
    assert( parcomm != NULL );
    Range meshCells;
    rval = mb->get_entities_by_dimension( initial_distributed_set, 2, meshCells );MB_CHK_SET_ERR( rval, "can't get cells by dimension from mesh set" );
 
    bool extraWork = (order >= 2);
    if( 1 == parcomm->proc_config().proc_size() )
    {
        // move all initial cells to coverage set
        rval = mb->add_entities( covering_set, meshCells );MB_CHK_SET_ERR( rval, "can't add primary ents to covering set" );
        // if point cloud source, add vertices
        if( 0 == meshCells.size() || max_edges_1 == 0 )
        {
            // add vertices from the source set
            Range verts;
            rval = mb->get_entities_by_dimension( initial_distributed_set, 0, verts );MB_CHK_SET_ERR( rval, "can't get vertices from mesh set" );
            rval = mb->add_entities( covering_set, verts );MB_CHK_SET_ERR( rval, "can't add primary ents to covering set" );
        }
        return MB_SUCCESS;
    }
 
    // mark on the coverage mesh where this element came from
    Tag sendProcTag;  /// for coverage mesh, will store the sender
    rval = mb->tag_get_handle( "sending_processor", 1, MB_TYPE_INTEGER, sendProcTag, MB_TAG_DENSE | MB_TAG_CREAT,
                               &defaultInt );MB_CHK_SET_ERR( rval, "can't create sending processor tag" );
 
    // this information needs to be forwarded to coverage mesh, if this mesh was already migrated
    // from somewhere else
    // look at the value of orgSendProcTag for one mesh cell; if -1, no need to forward that; if
    // !=-1, we know that this mesh was migrated, we need to find out more about origin of cell
    int orig_sender      = -1;
    EntityHandle oneCell = 0;
    // decide if we need to transfer global DOFs info attached to each HOMME coarse cell; first we
    // need to decide if the mesh has that tag; will affect the size of the tuple list involved in
    // the crystal routing
    int size_gdofs_tag = 0;
    std::vector< int > valsDOFs;
    Tag gdsTag;
    rval = mb->tag_get_handle( "GLOBAL_DOFS", gdsTag );
 
    if( meshCells.size() > 0 )
    {
        oneCell = meshCells[0];  // it is possible we do not have any cells, even after migration
        rval    = mb->tag_get_data( orgSendProcTag, &oneCell, 1, &orig_sender );MB_CHK_SET_ERR( rval, "can't get original sending processor value" );
        if( gdsTag )
        {
            DataType dtype;
            rval = mb->tag_get_data_type( gdsTag, dtype );
            if( MB_SUCCESS == rval && MB_TYPE_INTEGER == dtype )
            {
                // find the values on first cell
                int lenTag = 0;
                rval       = mb->tag_get_length( gdsTag, lenTag );
                if( MB_SUCCESS == rval && lenTag > 0 )
                {
                    valsDOFs.resize( lenTag );
                    rval = mb->tag_get_data( gdsTag, &oneCell, 1, &valsDOFs[0] );
                    if( MB_SUCCESS == rval && valsDOFs[0] > 0 )
                    {
                        // first value positive means we really need to transport this data during
                        // coverage
                        size_gdofs_tag = lenTag;
                    }
                }
            }
        }
    }
 
    // another collective call, to see if the mesh is migrated and if the GLOBAL_DOFS tag need to be
    // transferred over to the coverage mesh. It is possible that there is no initial mesh source
    // mesh on the task, so we do not know that info from the tag but TupleList needs to be sized
    // uniformly for all tasks.  Do a collective MPI_MAX to see if it is migrated and if we have
    // (collectively) a GLOBAL_DOFS task
 
    int local_int_array[2], global_int_array[2];
    local_int_array[0] = orig_sender;
    local_int_array[1] = size_gdofs_tag;
    // now reduce over all processors
    int mpi_err =
        MPI_Allreduce( local_int_array, global_int_array, 2, MPI_INT, MPI_MAX, parcomm->proc_config().proc_comm() );
    if( MPI_SUCCESS != mpi_err ) return MB_FAILURE;
    orig_sender    = global_int_array[0];
    size_gdofs_tag = global_int_array[1];
#ifdef VERBOSE
    std::cout << "proc: " << my_rank << " size_gdofs_tag:" << size_gdofs_tag << "\n";
#endif
    valsDOFs.resize( size_gdofs_tag );
 
    // finally, we have correct global info, we can decide if mesh was migrated and if we have
    // global dofs tag that need to be sent with coverage info
    int migrated_mesh = 0;
    if( orig_sender != -1 ) migrated_mesh = 1;  //
 
    int ghost_info = 0;
    if (extraWork)
        ghost_info = 1; // an extra field for ghost cell owner; we need it
    // if size_gdofs_tag>0, we are sure valsDOFs got resized to what we need
 
    // get all mesh verts1
    Range mesh_verts;
    rval = mb->get_connectivity( meshCells, mesh_verts );MB_CHK_SET_ERR( rval, "can't get  mesh vertices" );
    size_t num_mesh_verts = mesh_verts.size();
 
    // now see the mesh points positions; to what boxes should we send them?
    std::vector< double > coords_mesh( 3 * num_mesh_verts );
    rval = mb->get_coords( mesh_verts, &coords_mesh[0] );MB_CHK_SET_ERR( rval, "can't get mesh points position" );
 
    // decide gnomonic plane for each vertex, as in the compute boxes
    std::vector< int > gnplane;
    if( gnomonic )
    {
        gnplane.resize( num_mesh_verts );
        for( size_t i = 0; i < num_mesh_verts; i++ )
        {
            CartVect pos( &coords_mesh[3 * i] );
            int pl;
            IntxUtils::decide_gnomonic_plane( pos, pl );
            gnplane[i] = pl;
        }
    }
 
    std::vector< int > gids( num_mesh_verts );
    rval = mb->tag_get_data( gid, mesh_verts, &gids[0] );MB_CHK_SET_ERR( rval, "can't get vertices gids" );
 
    // ranges to send to each processor; will hold vertices and elements (quads/ polygons)
    // will look if the box of the mesh cell covers bounding box(es) (within tolerances)
    std::map< int, Range > Rto;
    int numprocs = parcomm->proc_config().proc_size();
 
    for( Range::iterator eit = meshCells.begin(); eit != meshCells.end(); ++eit )
    {
        EntityHandle q = *eit;
        const EntityHandle* conn;
        int num_nodes;
        rval = mb->get_connectivity( q, conn, num_nodes );MB_CHK_SET_ERR( rval, "can't get connectivity on cell" );
 
        // first decide what planes need to consider
        std::set< int > planes;  // if this list contains more than 3 planes, we have a very bad mesh!!!
        std::vector< double > elco( 3 * num_nodes );
        for( int i = 0; i < num_nodes; i++ )
        {
            EntityHandle v = conn[i];
            int index      = mesh_verts.index( v );
            if( gnomonic ) planes.insert( gnplane[index] );
            for( int j = 0; j < 3; j++ )
            {
                elco[3 * i + j] = coords_mesh[3 * index + j];  // extract from coords
            }
        }
        if( gnomonic )
        {
            // now loop over all planes that need to be considered for this element
            for( std::set< int >::iterator st = planes.begin(); st != planes.end(); st++ )
            {
                int pl         = *st;  // gnomonic plane considered
                double qmin[2] = { DBL_MAX, DBL_MAX };
                double qmax[2] = { -DBL_MAX, -DBL_MAX };
                for( int i = 0; i < num_nodes; i++ )
                {
                    CartVect dp( &elco[3 * i] );  // uses constructor for CartVect that takes a
                                                  // pointer to double
                    // gnomonic projection
                    double c2[2];
                    IntxUtils::gnomonic_projection( dp, Rsrc, pl, c2[0], c2[1] );  // 2 coordinates
                    for( int j = 0; j < 2; j++ )
                    {
                        if( qmin[j] > c2[j] ) qmin[j] = c2[j];
                        if( qmax[j] < c2[j] ) qmax[j] = c2[j];
                    }
                }
                // now decide if processor p should be interested in this cell, by looking at plane pl
                // 2d box this is one of the few size n loops;
                for( int p = 0; p < numprocs; p++ )  // each cell q can be sent to more than one processor
                {
                    double procMin1 = allBoxes[24 * p + 4 * ( pl - 1 )];  // these were determined before
                    //
                    if( procMin1 >= DBL_MAX )  // the processor has no targets on this plane
                        continue;
                    double procMin2 = allBoxes[24 * p + 4 * ( pl - 1 ) + 1];
                    double procMax1 = allBoxes[24 * p + 4 * ( pl - 1 ) + 2];
                    double procMax2 = allBoxes[24 * p + 4 * ( pl - 1 ) + 3];
                    // test overlap of 2d boxes
                    if( procMin1 > qmax[0] + box_error || procMin2 > qmax[1] + box_error ) continue;  //
                    if( qmin[0] > procMax1 + box_error || qmin[1] > procMax2 + box_error ) continue;
                    // good to be inserted
                    Rto[p].insert( q );
                }
            }
        }
        else  // regular 3d box; one box per processor
        {
            for( int p = 0; p < numprocs; p++ )
            {
                BoundBox box( &allBoxes[6 * p] );
                bool insert = false;
                for( int i = 0; i < num_nodes; i++ )
                {
                    if( box.contains_point( &elco[3 * i], box_error ) )
                    {
                        insert = true;
                        break;
                    }
                }
                if( insert ) Rto[p].insert( q );
            }
        }
    }
 
    // now, for higher order, we might need to send to processor p, not only the Range Rto[p] cells;
    // we need to augment those ranges with adjacent cells, according to the order passed
    // if order is 1, not do anything
    // if order is 2, for example, we need to add all adj cells level 1, by edge
    if (extraWork)
    {
        for (int p = 0; p < numprocs; p++ )
        {
            Range originalSend = Rto[p];
            // determine all adjacent cells for order 2 and higher
            // Need to get layers of bridge-adj entities
            if( originalSend.empty() ) continue;
            Range extraCells;
            rval  = MeshTopoUtil( mb ).get_bridge_adjacencies( originalSend, 0, 2, extraCells, order - 1 ); MB_CHK_SET_ERR( rval, "Failed to get bridge adjacencies" );
            // big miss : need to merge only cells from initial source (ghost) set;
            // get_bridge adj will get all cells adjacent to a vertex
            extraCells = intersect(extraCells, meshCells);
            Rto[p].merge(extraCells);
        }
    }
 
    // here, we will use crystal router to send each cell to designated tasks (mesh migration)
 
    // a better implementation would be to use pcomm send / recv entities; a good test case
    // pcomm send / receives uses point to point communication, not global gather / scatter
 
    // now, build TLv and TLq  (tuple list for vertices and cells, separately sent)
    size_t numq = 0;
    size_t numv = 0;
 
    // merge the list of vertices to be sent
    for( int p = 0; p < numprocs; p++ )
    {
        if( p == (int)my_rank ) continue;  // do not "send" it to current task, because it is already here
        Range& range_to_P = Rto[p];
        // add the vertices to it
        if( range_to_P.empty() ) continue;  // nothing to send to proc p
#ifdef VERBOSE
        std::cout << " proc : " << my_rank << " to proc " << p << " send " << range_to_P.size() << " cells "
                  << " psize: " << range_to_P.psize() << "\n";
#endif
        Range vertsToP;
        rval = mb->get_connectivity( range_to_P, vertsToP );MB_CHK_SET_ERR( rval, "can't get connectivity" );
        numq = numq + range_to_P.size();
        numv = numv + vertsToP.size();
        range_to_P.merge( vertsToP );
    }
 
    TupleList TLv;  // send vertices with a different tuple list
    TupleList TLq;
    TLv.initialize( 2, 0, 0, 3, numv );  // to proc, GLOBAL ID, 3 real coordinates
    TLv.enableWriteAccess();
 
    // add also GLOBAL_DOFS info, if found on the mesh cell; it should be found only on HOMME cells!
    int sizeTuple =
        2 + max_edges_1 + migrated_mesh + size_gdofs_tag + ghost_info;  // max edges could be up to MAXEDGES :) for polygons
    TLq.initialize( sizeTuple, 0, 0, 0,
                    numq );  // to proc, elem GLOBAL ID, connectivity[max_edges] (global ID v), plus
                             // original sender if set (migrated mesh case)
    // we will not send the entity handle, global ID should be more than enough
    // we will not need more than 2B vertices TODO 2B vertices or cells
    // if we need more than 2B, we will need to use a different marker anyway (GLOBAL ID is not
    // enough then)
 
    TLq.enableWriteAccess();
#ifdef VERBOSE
    std::cout << "from proc " << my_rank << " send " << numv << " vertices and " << numq << " elements\n";
#endif
 
    for( int to_proc = 0; to_proc < numprocs; to_proc++ )
    {
        if( to_proc == (int)my_rank ) continue;
        Range& range_to_P = Rto[to_proc];
        Range V           = range_to_P.subset_by_type( MBVERTEX );
 
        for( Range::iterator it = V.begin(); it != V.end(); ++it )
        {
            EntityHandle v = *it;
            int index      = mesh_verts.index( v );  //
            assert( -1 != index );
            int n                = TLv.get_n();             // current size of tuple list
            TLv.vi_wr[2 * n]     = to_proc;                 // send to processor
            TLv.vi_wr[2 * n + 1] = gids[index];             // global id needs index in the second_mesh_verts range
            TLv.vr_wr[3 * n]     = coords_mesh[3 * index];  // departure position, of the node local_verts[i]
            TLv.vr_wr[3 * n + 1] = coords_mesh[3 * index + 1];
            TLv.vr_wr[3 * n + 2] = coords_mesh[3 * index + 2];
            TLv.inc_n();  // increment tuple list size
        }
        // also, prep the 2d cells for sending ...
        Range Q = range_to_P.subset_by_dimension( 2 );
        for( Range::iterator it = Q.begin(); it != Q.end(); ++it )
        {
            EntityHandle q = *it;  // this is a second mesh cell (or src, lagrange set)
            int global_id;
            rval = mb->tag_get_data( gid, &q, 1, &global_id );MB_CHK_SET_ERR( rval, "can't get gid for polygon" );
            int n                    = TLq.get_n();  // current size
            TLq.vi_wr[sizeTuple * n] = to_proc;      //
            TLq.vi_wr[sizeTuple * n + 1] =
                global_id;  // global id of element, used to identify it for debug purposes only
            const EntityHandle* conn4;
            int num_nodes;  // could be up to MAXEDGES; max_edges?;
            rval = mb->get_connectivity( q, conn4, num_nodes );MB_CHK_SET_ERR( rval, "can't get connectivity for cell" );
            if( num_nodes > max_edges_1 )
            {
                mb->list_entities( &q, 1 );MB_CHK_SET_ERR( MB_FAILURE, "too many nodes in a cell (" << num_nodes << "," << max_edges_1 << ")" );
            }
            for( int i = 0; i < num_nodes; i++ )
            {
                EntityHandle v = conn4[i];
                int index      = mesh_verts.index( v );
                assert( -1 != index );
                TLq.vi_wr[sizeTuple * n + 2 + i] = gids[index];
            }
            for( int k = num_nodes; k < max_edges_1; k++ )
            {
                TLq.vi_wr[sizeTuple * n + 2 + k] =
                    0;  // fill the rest of node ids with 0; we know that the node ids start from 1!
            }
            int currentIndexIntTuple = 2 + max_edges_1;
            // is the mesh migrated before or not?
            if( migrated_mesh )
            {
                // case of extra work, maybe need to check if it is ghost ? yes, next loop !
                rval = mb->tag_get_data( orgSendProcTag, &q, 1, &orig_sender );MB_CHK_SET_ERR( rval, "can't get original sender for polygon, in migrate scenario" );
                TLq.vi_wr[sizeTuple * n + currentIndexIntTuple] = orig_sender;  // should be different than -1
                currentIndexIntTuple++;
            }
            if (ghost_info > 0) // extraWork
            {
                // case of ghost
                int owner = my_rank;
                // this could happen if extra work, real owner is different ?
                rval = parcomm->get_owner(q, owner); MB_CHK_SET_ERR( rval, "can't get owner for cell" );
                TLq.vi_wr[sizeTuple * n + currentIndexIntTuple] = owner;  // should be different than -1
                currentIndexIntTuple++;
            }
            // GLOBAL_DOFS info, if available
            if( size_gdofs_tag )
            {
                rval = mb->tag_get_data( gdsTag, &q, 1, &valsDOFs[0] );MB_CHK_SET_ERR( rval, "can't get gdofs data in HOMME" );
                for( int i = 0; i < size_gdofs_tag; i++ )
                {
                    TLq.vi_wr[sizeTuple * n + currentIndexIntTuple + i] =
                        valsDOFs[i];  // should be different than 0 or -1
                }
            }
 
            TLq.inc_n();  // increment tuple list size
        }
    }  // end for loop over total number of processors
 
    // now we are done populating the tuples; route them to the appropriate processors
    // this does the communication magic
    ( parcomm->proc_config().crystal_router() )->gs_transfer( 1, TLv, 0 );
    ( parcomm->proc_config().crystal_router() )->gs_transfer( 1, TLq, 0 );
 
    // the first mesh elements are in localEnts; we do not need them at all
 
    // maps from global ids to new vertex and cell handles, that are added
 
    std::map< int, EntityHandle > globalID_to_vertex_handle;
    // we already have some vertices from second mesh set; they are already in the processor, even
    // before receiving other verts from neighbors this is an inverse map from gid to vertex handle,
    // which is local here, we do not want to duplicate vertices their identifier is the global ID!!
    // it must be unique per mesh ! (I mean, first mesh, source); gid for second mesh is not needed here
    int k = 0;
    for( Range::iterator vit = mesh_verts.begin(); vit != mesh_verts.end(); ++vit, k++ )
    {
        globalID_to_vertex_handle[gids[k]] = *vit;
    }
    /*std::map<int, EntityHandle> globalID_to_eh;*/  // do we need this one?
    globalID_to_eh.clear();                          // we need it now in case of extra work, to not duplicate cells
 
    // now, look at every TLv, and see if we have to create a vertex there or not
    int n = TLv.get_n();  // the size of the points received
    for( int i = 0; i < n; i++ )
    {
        int globalId = TLv.vi_rd[2 * i + 1];
        if( globalID_to_vertex_handle.find( globalId ) ==
            globalID_to_vertex_handle.end() )  // we do not have locally this vertex (yet)
                                               // so we have to create it, and add to the inverse map
        {
            EntityHandle new_vert;
            double dp_pos[3] = { TLv.vr_wr[3 * i], TLv.vr_wr[3 * i + 1], TLv.vr_wr[3 * i + 2] };
            rval             = mb->create_vertex( dp_pos, new_vert );MB_CHK_SET_ERR( rval, "can't create new vertex " );
            globalID_to_vertex_handle[globalId] = new_vert;  // now add it to the map
            // set the GLOBAL ID tag on the new vertex
            rval = mb->tag_set_data( gid, &new_vert, 1, &globalId );MB_CHK_SET_ERR( rval, "can't set global ID tag on new vertex " );
        }
    }
 
    // now, all necessary vertices should be created
    // look in the local list of 2d cells for this proc, and add all those cells to covering set
    // also
 
    Range& local  = Rto[my_rank];
    Range local_q = local.subset_by_dimension( 2 );
 
    for( Range::iterator it = local_q.begin(); it != local_q.end(); ++it )
    {
        EntityHandle q = *it;  // these are from source cells, local
        int gid_el;
        rval = mb->tag_get_data( gid, &q, 1, &gid_el );MB_CHK_SET_ERR( rval, "can't get global id of cell " );
        assert( gid_el >= 0 );
        globalID_to_eh[gid_el] = q;  // do we need this? yes, now we do; parent tags are now using it heavily
        if (extraWork)
        {
            int owner = my_rank;
            // this could happen if extra work, real owner is different ?
            rval = parcomm->get_owner(q, owner); MB_CHK_SET_ERR( rval, "can't get owner for cell" );
            rval = mb->tag_set_data( sendProcTag, &q, 1, &owner );MB_CHK_SET_ERR( rval, "can't set sender for cell" );
        }
        else
        {
            rval = mb->tag_set_data( sendProcTag, &q, 1, &my_rank );MB_CHK_SET_ERR( rval, "can't set sender for cell" );
        }
    }
 
    // now look at all elements received through; we do not want to duplicate them
    n = TLq.get_n();  // number of elements received by this processor
    // a cell should be received from one proc only; so why are we so worried about duplicated
    // elements? a vertex can be received from multiple sources, that is fine
 
    for( int i = 0; i < n; i++ )
    {
        int globalIdEl = TLq.vi_rd[sizeTuple * i + 1];
        // int from_proc=TLq.vi_rd[sizeTuple * i ]; // we do not need from_proc anymore
 
        // do we already have a cell with this global ID, represented?
        // yes, it could happen for extraWork !
        if (globalID_to_eh.find(globalIdEl) != globalID_to_eh.end())
             continue;
        // construct the conn triangle , quad or polygon
        EntityHandle new_conn[MAXEDGES];  // we should use std::vector with max_edges_1
        int nnodes = -1;
        for( int j = 0; j < max_edges_1; j++ )
        {
            int vgid = TLq.vi_rd[sizeTuple * i + 2 + j];  // vertex global ID
            if( vgid == 0 )
                new_conn[j] = 0;  // this can actually happen for polygon mesh (when we have less
                                  // number of vertices than max_edges)
            else
            {
                assert( globalID_to_vertex_handle.find( vgid ) != globalID_to_vertex_handle.end() );
                new_conn[j] = globalID_to_vertex_handle[vgid];
                nnodes      = j + 1;  // nodes are at the beginning, and are variable number
            }
        }
        EntityHandle new_element;
        //
        EntityType entType = MBQUAD;
        if( nnodes > 4 ) entType = MBPOLYGON;
        if( nnodes < 4 ) entType = MBTRI;
        rval = mb->create_element( entType, new_conn, nnodes, new_element );MB_CHK_SET_ERR( rval, "can't create new element for second mesh " );
 
        globalID_to_eh[globalIdEl] = new_element;
        local_q.insert( new_element );
        rval = mb->tag_set_data( gid, &new_element, 1, &globalIdEl );MB_CHK_SET_ERR( rval, "can't set gid for cell " );
        int currentIndexIntTuple = 2 + max_edges_1;
        if( migrated_mesh )
        {
            orig_sender = TLq.vi_wr[sizeTuple * i + currentIndexIntTuple];
            rval        = mb->tag_set_data( orgSendProcTag, &new_element, 1, &orig_sender );MB_CHK_SET_ERR( rval, "can't set original sender for cell, in migrate scenario" );
            currentIndexIntTuple++;  // add one more
        }
        // store also the processor this coverage element came from
        int from_proc = TLq.vi_rd[sizeTuple * i];
        if( ghost_info ) // ghost info will have the original owner of the coverage cell
        {
            // case of ghost
           from_proc = TLq.vi_wr[sizeTuple * i + currentIndexIntTuple];
           currentIndexIntTuple++;  // add one more
        }
        rval = mb->tag_set_data( sendProcTag, &new_element, 1, &from_proc );MB_CHK_SET_ERR( rval, "can't set sender for cell" );
 
        // check if we need to retrieve and set GLOBAL_DOFS data
        if( size_gdofs_tag )
        {
            for( int j = 0; j < size_gdofs_tag; j++ )
            {
                valsDOFs[j] = TLq.vi_wr[sizeTuple * i + currentIndexIntTuple + j];
            }
            rval = mb->tag_set_data( gdsTag, &new_element, 1, &valsDOFs[0] );MB_CHK_SET_ERR( rval, "can't set GLOBAL_DOFS data on coverage mesh" );
        }
 
    }
 
    // now, add to the covering_set the elements created in the local_q range
    rval = mb->add_entities( covering_set, local_q );MB_CHK_SET_ERR( rval, "can't add entities to new mesh set " );
#ifdef VERBOSE
    std::cout << " proc " << my_rank << " add " << local_q.size() << " cells to covering set \n";
#endif
    return MB_SUCCESS;
}
 
#endif  // MOAB_HAVE_MPI
//#undef VERBOSE
#undef CHECK_CONVEXITY
 
} /* namespace moab */