code: int getGeometryUserIndex(int geom, int index) {
  		int pindex = getGeometryIndex_(geom);
  		AttributeStreamOfInt32 stream = m_geometry_indices.get(index);
  		if (pindex < stream.size())
  			return stream.read(pindex);
  		else
  			return -1;
  	}
docs: Returns the value of the given user index of a geometry