LoadPartial.cpp

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/**
 * @file LoadPartial.cpp
 * @brief Example demonstrating partial loading of mesh files based on tag values
 *
 * This example shows how to:
 * - Load only specific parts of a mesh file based on tag values
 * - Use parallel partition tags to load specific partitions
 * - Handle file organization in sets for selective loading
 * - Work with HANDLEID tags for entity identification
 * - Write partial mesh data to new files
 *
 * This is particularly useful for parallel applications where each
 * processor needs to load only its assigned portion of a large mesh.
 *
 * @author MOAB Development Team
 * @date 2024
 *
 
 * \brief Load a part of a file  \n
 * <b>To run</b>: LoadPartial [file] [tag_name] [val1] [val2] ...\n
 *
 * In this example, it is shown how to load only a part of one file; the file must be organized in
 * sets. (cherry-picking only the sets we want) The sets to load are identified by a tag name and
 * the tag values for the sets of interest. This procedure is used  when reading in parallel, as
 * each processor will load only its part of the file, identified either by partition or by
 * material/block sets by default, this example will load parallel partition sets with values 1, 2,
 * and 5 from ../MeshFiles/unittest/64bricks_1khex.h5m The example will always write the output to a
 * file name part.h5m
 *
 * @param argc Number of command line arguments
 * @param argv Command line arguments array
 * @return 0 on success, 1 on failure
 */
 
#include <iostream>
#include <vector>
 
// Include header for MOAB instance and tag conventions for
#include "moab/Core.hpp"
#include "MBTagConventions.hpp"
 
#define NTAGVALS 3
 
using namespace moab;
using namespace std;
 
// Function to parse input parameters
ErrorCode get_file_options( int argc, char** argv, string& filename, string& tagName, vector< int >& tagValues )
{
    // Get mesh filename
    if( argc > 1 )
        filename = string( argv[1] );
    else
        filename = string( MESH_DIR ) + string( "/64bricks_512hex_256part.h5m" );
 
    // Get tag selection options
    if( argc > 2 )
        tagName = string( argv[2] );
    else
        tagName = "USERTAG";
 
    if( argc > 3 )
    {
        tagValues.resize( argc - 3, 0 );
        for( int i = 3; i < argc; ++i )
            tagValues[i - 3] = atoi( argv[i] );
    }
    else
    {
        for( unsigned i = 0; i < tagValues.size(); ++i )
            tagValues[i] = 2 * i + 1;
    }
 
    if( argc > 1 && argc < 4 )  // print usage
        cout << " usage is " << argv[0] << " <file> \c tag_name <value1> <value2> .. \n";
    return MB_SUCCESS;
}
 
int main( int argc, char** argv )
{
    // Get MOAB instance
    Interface* mb = new( std::nothrow ) Core;
    if( NULL == mb ) return 1;
 
    std::string filename, tagname;
    vector< int > tagvals( NTAGVALS );  // Allocate for a maximum of 5 tag values
    MB_CHK_ERR( get_file_options( argc, argv, filename, tagname, tagvals ) );
 
#ifdef MOAB_HAVE_HDF5
    // This file is in the mesh files directory
    MB_CHK_SET_ERR( mb->load_file( filename.c_str(), 0, 0, PARALLEL_PARTITION_TAG_NAME, tagvals.data(),
                                   (int)tagvals.size() ),
                    "Failed to read" );
 
    // If HANDLEID tag present, convert to long, and see what we read from file
    Tag handleid_tag;
    ErrorCode rval = mb->tag_get_handle( "HANDLEID", handleid_tag );
    if( MB_SUCCESS == rval )
    {
        // Convert a few values for a few vertices
        Range verts;
        MB_CHK_SET_ERR( mb->get_entities_by_type( 0, MBVERTEX, verts ), "Failed to get vertices" );
        vector< long > valsTag( verts.size() );
        rval = mb->tag_get_data( handleid_tag, verts, &valsTag[0] );
        if( MB_SUCCESS == rval ) cout << "First 2 long values recovered: " << valsTag[0] << " " << valsTag[1] << "\n";
    }
 
    MB_CHK_SET_ERR( mb->write_file( "part.h5m" ), "Failed to write partial file" );
    cout << "Wrote successfully part.h5m.\n";
 
#else
    std::cout << "Configure MOAB with HDF5 to build and use this example correctly.\n";
#endif
    delete mb;
    return 0;
}