QuadTriConv.cpp File Reference

Example demonstrating conversion of repeated-vertex cells to triangles/quads/polygons. More...

#include <iostream>
#include <vector>
#include "moab/Core.hpp"
#include "MBTagConventions.hpp"

Include dependency graph for QuadTriConv.cpp:

Go to the source code of this file.

Functions
int	main (int argc, char **argv)

Detailed Description

Example demonstrating conversion of repeated-vertex cells to triangles/quads/polygons.

This example shows how to:

• Load a mesh file with repeated vertices in 2D cells (e.g., at poles)
• Merge repeated vertices in cell connectivity
• Convert cells to triangles, quads, or polygons as appropriate
• Preserve global ID tags during conversion
• Write the modified mesh to a new file

This is useful for cleaning up rll meshes or other grids with repeated vertices at the poles or other singularities.

Author

MOAB Development Team

Date

2024

Merge vertices in 2d cell, if they are repeated
To run: QuadTriConv input_file output_file
In this example, a mesh that has vertices repeated due to south or north pole, for example in an rll mesh, need to be converted to triangles, preserving GLOBAL_ID tag

Parameters

argc	Number of command line arguments
argv	Command line arguments array

Returns

0 on success, 1 on failure

Definition in file QuadTriConv.cpp.

Function Documentation

main()

int main	(	int	argc,
		char **	argv
	)

Definition at line 41 of file QuadTriConv.cpp.

{
    // Get MOAB instance
    Interface* mb = new( std::nothrow ) Core;
    if( NULL == mb ) return 1;
 
    std::string filename, outfile;
    outfile = string( "out.h5m" );
    if( argc == 1 ) return 0;
    if( argc > 1 ) filename = string( argv[1] );
    if( argc > 2 ) outfile = string( argv[2] );
 
    // This file is in the mesh files directory
    MB_CHK_SET_ERR( mb->load_file( filename.c_str() ), "Failed to read" );
 
    // get all cells of dimension 2;
    Range cells;
    MB_CHK_SET_ERR( mb->get_entities_by_dimension( 0, 2, cells ), "Failed to get cells" );
 
    cout << " number of cells : " << cells.size() << "\n";
 
    Tag gid;  // global id tag
    MB_CHK_SET_ERR( mb->tag_get_handle( "GLOBAL_ID", gid ), "Failed to get Global ID tag" );
 
    Range modifiedCells;  // will be deleted at the end; keep the gid
 
    for( Range::iterator cit = cells.begin(); cit != cells.end(); cit++ )
    {
        EntityHandle cell          = *cit;
        const EntityHandle* connec = NULL;
        int num_verts              = 0;
        MB_CHK_SET_ERR( mb->get_connectivity( cell, connec, num_verts ), "Failed to get connectivity" );
 
        vector< EntityHandle > newConnec;
        newConnec.push_back( connec[0] );  // at least one vertex
        int index    = 0;
        int new_size = 1;
        while( index < num_verts - 2 )
        {
            int next_index = ( index + 1 );
            if( connec[next_index] != newConnec[new_size - 1] )
            {
                newConnec.push_back( connec[next_index] );
                new_size++;
            }
            index++;
        }
        // add the last one only if different from previous and first node
        if( ( connec[num_verts - 1] != connec[num_verts - 2] ) && ( connec[num_verts - 1] != connec[0] ) )
        {
            newConnec.push_back( connec[num_verts - 1] );
            new_size++;
        }
        if( new_size < num_verts )
        {
            // cout << "new cell from " << cell << " has only " << new_size << " vertices \n";
            modifiedCells.insert( cell );
            // create a new cell with type triangle, quad or polygon
            EntityType type = MBTRI;
            if( new_size == 3 )
                type = MBTRI;
            else if( new_size == 4 )
                type = MBQUAD;
            else if( new_size > 4 )
                type = MBPOLYGON;
 
            // create new cell
            EntityHandle newCell;
            MB_CHK_SET_ERR( mb->create_element( type, &newConnec[0], new_size, newCell ), "Failed to create new cell" );
            // set the old id to the new element
            int id;
            MB_CHK_SET_ERR( mb->tag_get_data( gid, &cell, 1, &id ), "Failed to get global id" );
            MB_CHK_SET_ERR( mb->tag_set_data( gid, &newCell, 1, &id ), "Failed to set global id on new cell" );
        }
    }
 
    mb->delete_entities( modifiedCells );
    // in case global ids are not set for vertices, set them, in order;
    // they are needed for migrating later on
    //
    Range verts;
    MB_CHK_SET_ERR( mb->get_entities_by_dimension( 0, 0, verts ), "Failed to get vertices" );
 
    vector< int > gids;
    gids.resize( verts.size() );
    MB_CHK_SET_ERR( mb->tag_get_data( gid, verts, &gids[0] ), "Failed to get gids on vertices" );
    if( gids[0] <= 0 )
    {
        // gids were never set, assign them
        for( size_t i = 1; i <= verts.size(); i++ )
            gids[i - 1] = (int)i;
        MB_CHK_SET_ERR( mb->tag_set_data( gid, verts, &gids[0] ), "Failed to set gids on vertices" );
    }
    MB_CHK_SET_ERR( mb->write_file( outfile.c_str() ), "Failed to write new file" );
 
    cout << " wrote file " << outfile << " with " << modifiedCells.size() << " modified cells\n";
 
    delete mb;
    return 0;
}

References moab::Range::begin(), moab::Core::create_element(), moab::Core::delete_entities(), moab::Range::end(), moab::Core::get_connectivity(), moab::Core::get_entities_by_dimension(), moab::index, moab::Range::insert(), moab::Core::load_file(), mb, MB_CHK_SET_ERR, MBPOLYGON, MBQUAD, MBTRI, moab::Range::size(), moab::Core::tag_get_data(), moab::Core::tag_get_handle(), moab::Core::tag_set_data(), and moab::Core::write_file().