Getting element entity from vertex handle

[In-hak Min]

Is there API to query element entities handle from used vertex?

[Vijay M]

You can query the adjacencies for the vertex and it should give you the entity handles for all the elements containing it.

[In-hak Min]

Thanks for reply.

I am trying about you mentioned and write the code below.

vertex handle 1 is used where hex elements 1 and 2.

but adjacencies size is 0 from vertex handle 1.

What is wrong?

‌

moab::Core *mb;

int main()
{
    mb = new moab::Core();

    const unsigned NUMVTX = 27;  // The number of vertexes
    const unsigned NUMHEX = 8;   // The number of hexahedrons

    // This double array stores the x, y, z coordinate of each vertex.
    const double vertex_coords[3 * NUMVTX] = {
        0, 0, 0, 1, 0, 0, 2, 0, 0, 0, 1, 0, 1, 1, 0, 2, 1, 0, 0, 2, 0, 1, 2, 0, 2, 2, 0,
        0, 0, 1, 1, 0, 1, 2, 0, 1, 0, 1, 1, 1, 1, 1, 2, 1, 1, 0, 2, 1, 1, 2, 1, 2, 2, 1,
        0, 0, 2, 1, 0, 2, 2, 0, 2, 0, 1, 2, 1, 1, 2, 2, 1, 2, 0, 2, 2, 1, 2, 2, 2, 2, 2
    };

    moab::EntityHandle conn[NUMHEX][2] = { 
        { 1, 2, 5, 4, 10, 11, 14, 13 },      { 2, 3, 6, 5, 11, 12, 15, 14 } };

    moab::ErrorCode rval;
    for(int i=0; i<NUMVTX; i++) {
        float x = vertex_coords[i*3];
        float y = vertex_coords[i*3+1];
        float z = vertex_coords[i*3+2];
        std::vector<double> coord(3);
        coord[0] = x;
        coord[1] = y;
        coord[2] = z;
        moab::EntityHandle h;
        rval = mb->create_vertex( coord.data(), h );
    }

    for(int i=0; i<2; i++) {
        moab::EntityHandle element;

        // add hexahedron
        moab::Range range;
        rval = mb->create_element( moab::MBHEX, conn[i], 8, element );

        range.insert( element );
        mb->add_entities(0, range);
    }

    int count;
    mb->get_number_entities_by_type(0, moab::MBHEX, count);
    printf("Total hex count is %d\n", count);

    // getting element from vertex handle
    std::vector<moab::EntityHandle> from_entities;
        moab::EntityHandle entity;
        mb->handle_from_id(moab::MBVERTEX, 2, entity);
        from_entities.push_back(entity);

    std::vector<moab::EntityHandle> adjacencies;
    mb->get_adjacencies( from_entities.data(), 2, 1, false, adjacencies );
    printf("adjacencies: %d\n", adjacencies.size());

    delete mb;
}

Total hex count is 2
adjacencies: 0

[Iulian Grindeanu]

mb->get_adjacencies( from_entities.data(), 2, 1, false, adjacencies );
is wrong
it should be mb->get_adjacencies( from_entities.data(), /*number of entities*/1, /*dimension*/ 3, false, adjacencies );
look at interface:
virtual ErrorCode get_adjacencies( const EntityHandle* from_entities, const int num_entities,
const int to_dimension, const bool create_if_missing,
std::vector< EntityHandle >& adj_entities,
const int operation_type = Interface::INTERSECT ) = 0;

‌

[Iulian Grindeanu]

also, this part of the code is not efficient:
`for(int i=0; i<2; i++) { moab::EntityHandle element;

    // add hexahedron
    moab::Range range;
    rval = mb->create_element( moab::MBHEX, conn[i], 8, element );

    range.insert( element );
    mb->add_entities(0, range);
}

`

should be

moab::Range range;
` for(int i=0; i<2; i++) { moab::EntityHandle element;

    // add hexahedron

    rval = mb->create_element( moab::MBHEX, conn[i], 8, element );

    range.insert( element );

}

mb->add_entities(0, range);`

Also,
moab::EntityHandle conn[NUMHEX][2] = { { 1, 2, 5, 4, 10, 11, 14, 13 }, { 2, 3, 6, 5, 11, 12, 15, 14 } };

Should be
moab::EntityHandle conn[2][NUMHEX] = { { 1, 2, 5, 4, 10, 11, 14, 13 }, { 2, 3, 6, 5, 11, 12, 15, 14 } };

[In-hak Min]

Thank you.

Your point was very useful for me.

I resolved this issue. ​