function render() {
    if(has_children()) {
        for(child in children) {
            if(child.bounds.intersect(viewing_frustum)) {
                if(lod_threshold_reached) {
                    draw_terrain_mesh();
                } else {
                    child.render();
                }
            }
        }
    } else {
        draw_terrain_mesh();
    }
}

function calc_cells_in_quadrilateral(frustum_projection_onto_2d_terrain_grid) {
    //calculate cells in the resulting quadrilateral projection of the frustum onto the grid without having to bounds test every cell
    //at some point based on distance from camera, assign lod
}
retrieve lod for each cell in the calculated set from lod grids
have multiple (array2 or intmap) containing the terrain data at every lod for O(1) retrieval