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Alignment woes - any new tricks to try

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Alignment woes - any new tricks to try

Postby MrPete » Mon Jun 14, 2010 1:25 am

With all the help on the forum have got the recipe for the most part of getting clean scans with lots of detail.
Trying to align/combine the individual scans is another story. The scans have been taken from four sides N,S,E,W orientation with 3 in each side. N1,N2 and N3 seem to go together okay ( I wonder just how accurate the global fine registration is doing?). All the files on a side are saved as a combined file. Now comes the rub, can't seem to get the four sides to make a closed model. Have tried using fine registration after doing a careful manual alignment, it just doesn't seem to want to see the edges. Using the global fine registration lips parts inside out or to a position only it could have picked??? Have also tried manual three point alignment, just can't seem to get it close enough to close the model.

After all that went back and tried rescanning the model to get more of an overlap on the edges with much the same results. I'm guessing that the crisp edge is going to be a hard one to align. I'm hoping someone in the forum has come across this kind of issue and has a solution for it.

The first picture is the complete combined model called up as an STL file in another CAD program.
The second picture is the combined model after alignment and in the process of manual alignment.
Attachments
Slide1.jpg
Slide2.jpg
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Re: Alignment woes - any new tricks to try

Postby funtasma » Mon Jun 14, 2010 6:38 am

There is simply not enough overlapping. In those cases you need to make it completely manually or do additional scans. If the object would have a texture with very distinct patterns could also help, but still you would need a clear overlap. Scan the edges and the nose of the object to have something DAVID can work with.

Maybe this can help you:
viewtopic.php?f=10&t=1835

-Benjamin-
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Re: Alignment woes - any new tricks to try

Postby MrPete » Thu Jun 17, 2010 1:44 am

Benjamin,

Thanks for the advice, seems like it's going to do the trick.

Did some very rough testing and showed a great deal of improvement. Took a pencil and marked the model on part lines (takes 3 scans to do the full length so divided it into thirds). This provides a good deal of overlap and a reference line for alignment. The laser was run at a much higher sweep rate to facilitate quick tests (lots of gaps/holes). Even with the degraded scans the edges lined up much better. Due to the shape of the model the edges always run off a bit, ended up doing some trimming to clean up the model during assembly of the individual scans.

Given the lesson learned above think I'm going to try adding pencil lines along the long axis of the model to indicate trim lines given a view orientation. Since the model is scanned from four sides wil break it into fourths along the long axis.

Reading up some more on the forum will try meshlab for filling the holes and eliminating some of the noise in the final combined scan model.

Thanks again, Pete
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