agreed, the two-screen, three-point alignment system is finicky and needlessly complex. All you need is pan, scale, and rotate functions to get the job done. Much more intuitive.
What it's doing is setting ground control points that can be passed to a tool like gdal_translate[1]. That three-point alignment deal is setting three pairs of points made up of a lat,lng on the world, and an x,y on the image. Most world map projections cause distortion that can't be compensated for with just pan, scale, and rotate. The GCP jazz can.
But I'm in agreement, their UI to set the GCPs is terrible. :-P
Good call. Looking into this further, looks like you're right.[1] For the Mercator projection, translate, scale, and rotate are sufficient for the georectification of small images (read: floorplans). You'd need more of the affine toolbox if you used something like Mollweide (mostly sheer, right?), and then you might need non-affine stuff to deal with crazier projections.
I guess, then, that begs the question of why the Google floorplan submission UI uses that weird double-pane thing?
