I'm PR'ing this as a draft to show a test I think we should have, and to raise as an issue the coordinate convention headache that one might hit if they do a couple of localization processes using recipe modules.
Namely:

• DetectPoints2D output is in units of pixels, not units of nanometers
• FitPoints requires input positions to be in units of nanometers
• Between density mapping and FitPoints one picks up a half-pixel shift.

Would love to hear some thoughts on preferred way to fix some of these @David-Baddeley !
My thought would be to:

• multiply DetectPoints2D by voxelsize_nm.x and voxelsize_nm.y
• fix the fixme in visHelpers.rendGauss about im[0,0] centering
• write a documentation page about coordinate conventions in PYMEVis / PYMEImage