Is it possible to reset ground control points to "null" once they have been set? In my case, I thought the photos had locations in the EXIF headers -- it turns out the photos did not have this info. The locations were set to 0.000, 0.000, 0.000. But this meant that the area of the entire pointcloud/photoset was reduced to a single point. I cannot find a way of clearing that information (entering a null value ends up with 0.000 in each of the x,y,z boxes).