Grid map can contain multiple map layers
The following map is constructed with one layer called “elevation”.
using namespace grid_map;
GridMap map({"elevation"});
for (GridMapIterator it(map); !it.isPastEnd(); ++it){
Position position;
map.getPosition(*it, position);
map.at("elevation", *it) = -0.04 + 0.2 * std::sin(3.0 * time.toSec() + 5.0 * position.y()) * position.x();
}