I think AntoineM's answer was perhaps deliberately somewhat teasing/provocative when he says 'Getting an RMS lower than 1.3 is very easy, you just have to clean more points'.
Fact is: having a good RMS you have a good stitch. My praxis - PRAXIS - shows that i NEED a RMS of max. 1.3 for having an error-free stitch with 700mpx and higher when zooming in to 100%. What´s your average size of equis, Andrew and Antoine?
I think he's saying that there's a difference between reducing RMS to below 1.3 and achieving a good stitch.
I know what i do, Andrew - and i know what i need
Shooting and stitching a pano using a fisheye is easy (well: more or less, depending on the stitcher
But shooting hires panos with 42 or 214 images is quite different edit-wise. Here i realized - you will not be able to prove the opposite - that
i need to have at least RMS of 1.3 for having NO errors when zooming to 100%.
RMS 2 for example needs me to critically investigate the *whole* equi in Photoshop for hours for finding errors and retouching them.
As I understand it optimising in APG is not the same as optimising in PTGui, in the latter reducing the 'magic number' - forgotten what their statistic of goodness of fit is called - is always deemed to be better.
In PTGui i don´t have these issues. PTGui provides magnifying tools for editing on images for seeing what happens. It lets me pixel-precise edit CPs manually in realtime @100%.
But that´s rarely needed. Good to have anyway. IF there ever are HEAVY issues with CPs i can use the mask-tool for masking bad areas in overlaps - this way
ANY stitch can be done perfectly.
I needed to do it only twice - when i made mistakes by not tightening the screw for the camera-rail on the head when it took the Zenith shot: the rail slipped two centimeters when the head shot the upper row and then did the Zenith shot:
35mm, 42 shots, 20% overlap indoors: http://www.360impressions.de/Klap
- multires on tablets also.
I usually do not at all count on numbers alone. But there definitely is
a coherence between the number of RMS and a good stitch.
What might RMS values tell us otherwise??
Again: a pano with 6 or 7 fisheye shots using a crop camera can work well with RMS of 2.5 or even 3 - you simply do not see minor erors even at 100%. But use a D800 with a 16mm fisheye providing 180MPx . . . and the whole thing looks very
diffenent @100% - believe me . .
Again #2 as said already: a D800 with a 35mm lens provides about 1,2GPx. Looking on the stitch @ 100% will teach you to think about it totally different . . .
Maybe even in that case RMS of 2 or more MIGHT
work without errors - i don´t know - but you CANNOT BE SURE
Producing commercially/professionally i NEED
to be sure to work with NO visible errors
as far as it´s possible!
Ain´t not too hard to accept, is it . .