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Aligning 220 Hi-Res Scans....

Problems, solutions and discussion about scanning with a video projector and stripe patterns.

Aligning 220 Hi-Res Scans....

Postby FSAE_Junkie » Thu Mar 27, 2014 4:11 am

I have been attempting to scan the underside of my car for 'fitment' of an upcoming project. Because the bottom of the car is only ~20" or so off of the ground, I have to resort to many scans of small areas. I am only part way through the scanning and I have ended up with 220 scans thus far.

One painful thing with this scan in particular is that alignment is a nightmare. I've been roughly aligning as I go, but due to constantly pasting a new scan on a prior scan, the small errors begin to stack up. So, I'm having to go back through all of the scans and align them in a more methodical way, but it is very time consuming.

Anyways, I'm only about 20% of the way though a good re-alignment. But here's how it's looking so far:

Image

Image

One thing I've learned so far is that after calibrating, I have to set the min and max distance filters to filter out anything in front of the calibration panels or anything beyond them. This limits the scan region to about 10" of depth, but I have found that is all I can trust. If I don't set the filter and happen to pick up scan data that would be beyond the calibration panels, it will look correct but this is deceiving. If I move the scanner closer by say 10" (placing the scan area the same distance the calibration panels were) and scan that same region, the 2 scans end up not being the same size. I take this to mean that the depth of field of the optics start to introduce geometry errors when you get outside the region of the calibration panels. It's just tricky because it's not immediately obvious what is accurate in the scan.

In the future, maybe I need to do a test immediately after calibration with some long straight edges to see at what distances the optics start to distort the result.

If anybody has done anything similar, I would be interested to hear any comments or advice or questions.
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