Hmm; I think the approach is correct here...the only problem with the polar projection is the singularity at r=0, which is why it is specifically exempted.  The code should activate for everything else.

As for not having an inverted transformation, would that even make sense?  Not being able to go from pixel coordinates to data coordinates?  Seems like there would be quite a few other things that would break in that situation; not just this.