ContinentsOnGlobe.cpp

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/**
 * @file ContinentsOnGlobe.cpp
 * @brief Example demonstrating continent boundary detection on spherical meshes
 *
 * This example shows how to:
 * - Load spherical mesh files and continent boundary data
 * - Convert 3D spherical coordinates to 2D lat-lon coordinates
 * - Perform point-in-polygon tests for continent detection
 * - Create mesh sets for different continents and islands
 * - Tag mesh elements with continent information
 * - Handle complex boundary loops for major landmasses
 * - Write continent-mapped mesh files
 *
 * This tool is useful for climate and geophysical applications
 * where continent boundaries need to be identified on spherical meshes.
 *
 * @author MOAB Development Team
 * @date 2024
 *
 * @example ContinentsOnGlobe.cpp
 * Description: read a mesh on a sphere and boundaries of continents and major islands,
 *   and write a boundaries mesh file (bound.vtk) and a file with sets for major continents
 * (map.h5m). Boundaries exist as 2 files, a list of boundary points and a list of loops,
 * representing each continent and major islands; there are 796 loops (islands). The first one has
 * 1239 edges/segments (Asia+Europe), while the last one has only 3. It must be a small island :)
 *    ContinentsOnGlobe  <input.h5m>
 *  default values: poly2000.h5m : a mesh with 2000 polygons on a sphere of radius 1
 *
 * @param argc Number of command line arguments
 * @param argv Command line arguments array
 * @return 0 on success, 1 on failure
 */
 
#include "moab/Core.hpp"
#include "moab/ReadUtilIface.hpp"
#include <cmath>
#include "moab/CartVect.hpp"
 
#include <iostream>
#include <fstream>
 
using namespace moab;
using namespace std;
 
string bd_name    = string( MESH_DIR ) + string( "/../examples/earth/boundary_points.dat" );
string loops      = string( MESH_DIR ) + string( "/../examples/earth/SaveLoopCounts" );
string input_file = string( MESH_DIR ) + string( "/../examples/earth/poly2000.h5m" );
 
double getLat( CartVect p )
{
    p.normalize();
    return asin( p[2] );
}
double getLon( CartVect p )
{
    p.normalize();
    double lon;
 
    lon = atan2( p[1], p[0] );
 
    if( lon < -2.95 )
    {  // separate Asia/Europe from Americas
        return 2.0 * M_PI + lon;
    }
    else
    {
        return lon;
    }
}
 
// we project sphere points on a 2d map. We decide if a point is in interior of a loop
// with the span angle test; it will work for any island except Antarctica
 
bool interior_point( vector< double >& coords, int& startLoop, int& endLoop, double lat, double lon )
{
    // compute oriented angle between point and edges in the loop
    // if angle ~ +/-2Pi, it is in the interior
    double totalAngle = 0;
    for( int i = startLoop; i <= endLoop; i++ )
    {
        double x1 = coords[2 * i], y1 = coords[2 * i + 1];
        int i2 = i + 1;
        if( i == endLoop ) i2 = startLoop;
        double x2 = coords[2 * i2], y2 = coords[2 * i2 + 1];
        CartVect P1( x1 - lat, y1 - lon, 0. );
        CartVect P2( x2 - lat, y2 - lon, 0. );
        CartVect cross = P1 * P2;
        double angle1  = angle( P1, P2 );
        if( cross[2] < 0 ) angle1 = -angle1;
        totalAngle += angle1;
    }
    if( fabs( totalAngle + 2 * M_PI ) < 0.1 || fabs( totalAngle - 2 * M_PI ) < 0.1 ) return true;
    return false;
}
 
int main( int argc, char** argv )
{
    // Get MOAB instance
    Interface* mb = new( std::nothrow ) Core;
    if( NULL == mb ) return 1;
 
    if( argc > 1 )
    {
        // User has input file for mesh file
        input_file = argv[1];
    }
 
    cout << "input file : " << input_file << "\n";
    std::vector< double > coords;
    ifstream bdFile( bd_name.c_str() );
    if( !bdFile )
    {
        cout << endl << "Failed to open file " << bd_name << endl;
        ;
        return 1;
    }
    coords.resize( 0 );
    while( !bdFile.eof() )
    {
        double co;
        bdFile >> co;
        coords.push_back( co );
    }
    cout << " number of boundary points:" << coords.size() / 3 << "\n";
    /// get loops for boundaries
    vector< int > loopsindx;
    ifstream loopFile( loops.c_str() );
    while( !loopFile.eof() )
    {
        int indx;
        loopFile >> indx;
        loopsindx.push_back( indx );
    }
    cout << "number of loops: " << loopsindx.size() / 2 << "\n";
    // convert loops to lat-lon loops
    // it will be easier to determine in-out relations for points in 2d plane
    // careful with the international time zone; ( + - Pi longitude )
    vector< double > coords2d;
    coords2d.resize( coords.size() / 3 * 2 );
    for( int i = 0; i < (int)coords.size() / 3; i++ )
    {
        CartVect p( coords[3 * i], coords[3 * i + 1], coords[3 * i + 2] );
        coords2d[2 * i]     = getLat( p );
        coords2d[2 * i + 1] = getLon( p );
    }
 
    MB_CHK_SET_ERR( mb->load_file( input_file.c_str() ), "Can't load file" );
    // look at the center of element, and see if it is inside the loop
 
    Range cells;
    MB_CHK_SET_ERR( mb->get_entities_by_dimension( 0, 2, cells ), "Can't get cells" );
 
    cout << "number of cells: " << cells.size() << "\n";
 
    // tag for continents
    Tag tag1;
    int defa = -1;
    MB_CHK_SET_ERR( mb->tag_get_handle( "continent", 1, MB_TYPE_INTEGER, tag1, MB_TAG_DENSE | MB_TAG_CREAT, &defa ),
                    "Trouble creating continent tag" );
    EntityHandle islandSets[6];
    for( int loop_index = 0; loop_index < 6; loop_index++ )
    {
        MB_CHK_SET_ERR( mb->create_meshset( MESHSET_SET, islandSets[loop_index] ), "Can't create island set" );
        int startLoop = loopsindx[2 * loop_index];
        int endLoop   = loopsindx[2 * loop_index + 1];
 
        vector< EntityHandle > interiorCells;
        for( Range::iterator cit = cells.begin(); cit != cells.end(); cit++ )
        {
            EntityHandle cell = *cit;
            // see if it is in the interior of the loop
            CartVect center;
            MB_CHK_SET_ERR( mb->get_coords( &cell, 1, &( center[0] ) ), "Can't get cell center coords" );
            double lat = getLat( center ), lon = getLon( center );
            // if NA, use some boxes too, for lat/lon
            // if (NorthAmerica && (lat < 0.15 || lon < M_PI || lon > 2*M_PI - 0.5) )
            //  continue;
 
            if( interior_point( coords2d, startLoop, endLoop, lat, lon ) )
            {
                interiorCells.push_back( cell );
                MB_CHK_SET_ERR( mb->tag_set_data( tag1, &cell, 1, &loop_index ), "Can't get tag on cell" );
            }
        }
 
        MB_CHK_SET_ERR( mb->add_entities( islandSets[loop_index], &interiorCells[0], interiorCells.size() ),
                        "Can't add entities to set" );
    }
 
    std::stringstream islandFile;
 
    islandFile << "map.h5m";
 
    MB_CHK_SET_ERR( mb->write_file( islandFile.str().c_str() ), "Can't write island file" );
    return 0;
}