A few questions popped into mind after reading you comments on subsampling:
1. Can anyone actually confirm the type of subsampling that is being used? From the use of "average subsampling point distance" you would think that a spatial filter is being used, but if not the effect that random decimation or row/column reduction would be dramatically different. My hunch says spatial filter, but I am uncertain it is that simple.
2. Also, do we know if scans of different resolutions are subsampled the same or if they are sampled proportionally to their original resolution? Maybe we should think about what part of the process is "averaged"?
3. With respect to your comment here:
I completely agree with the logic here, but I have often wondered if a high subsampling is used during registration then are high and low resolution scans treated effectively the same with no perceivable difference in the registration results? Scanning at higher resolutions give you more opportunity to utilize lower subsampling, but I have found the point of diminishing returns approaches quickly for most environments. I think the only time it would make sense to scan at high resolutions is when you have very fine details that are visible across the project over great distances that need to be aligned very well. Alternatively I would think that scanning in a "perfect room" like I described earlier would produce the same results regardless of the resolution it was scanned, so scanning it at 1:1 would obviously be a waste if 1/8th or 1/16th resolutions registered nearly the same. Basically the scanned environment can dictate the C2C success more than the resolution, but they are both factors that need to be considered. I hope that made sense and my logic sound, but I am still uncertain.I'd like to add that the density at which you had taken your scans, whether 1/4th, 1/5th, 1/8th, and the distance at which you've spaced your scan setups in the field, will highly change the effectiveness of subsampling. Since the density of points get less and less dense as you get farther from the scanner, if you've got lower res scans (i.e. 1/8th) you really want to keep more of your points, hence a lower subsample on lower res scans, to attain better registration results.
Just as an fyi:
I just scanned half a dozen sites this week that I have scanned and registered in the past using C2C, and I must say there was far less effort in helping the registration process along this time. Yesterday, I registered (80) 1/8th res scans in just two steps, top down then cloud to cloud. No adjustments were made during or after. Last time I tried this I ran into significant problems that took multiple adjustments to resolve. It is very nice to see this kind of improovement in 5.5 Thanks again Faro Devs!