In 2006, I've been asked to produce an orthophoto of a dam elevation than could be used to locate disorders in the concrete surface.

To maintain a relatively accurate distance measurement along the surface of the image, I proposed to use a cone as the surface of projection.

 

The Fabreges dam, its 3D mesh and the 3D model of the conical surface of projection

That was quite a special work, with lots of problems dealing with calibrating big telephoto lens, using very long range 3D scanner, programming specific orthorectification software. But there it is !

click to enlarge

The big red footprints have been painted by activists against the reintroduction of bears in the Pyrenees.