UAV photogrammetry in PostGIS – orthorectification

In the previous recipe, we explored the initial steps in photogrammetric processing, with PostGIS as our storage endpoint for the point cloud derived from aerial imagery. The next step is to create imagery from this point cloud in the plan view, that is, in 2D map coordinates.

To derive the plan view orthophotography from the point cloud, we need to do several things. First, we need a method to convert the point cloud to a 2D areal representation. We could use formal interpolation; but, for the sake of simplicity, we will do this using Voronoi polygons, a space-filling approach that allows us to convert our points to polygons. Next, we need to attribute those polygons with the colors derived from the original imagery. Finally, we need to render those polygons to raster.

This is not a complete orthorectification approach and fails badly where our point cloud is least dense; but, in the absence of a drape function with a PostGIS raster for draping...