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Tricky fusion

The place for all topics related to the 'Shapefusion' tool of DAVID.

Tricky fusion

Postby Gui » Mon Dec 03, 2012 10:50 am

Dear friends,

In my internship I manufacture some carbon fibre plates with different parameters and now I'm using DAVID Scanner to try to evaluate the distortions in each plate.

Right now I'm just making one scan of the rear surface and one scan of the front surface, because I had big difficulties while trying to fuse the whole plate from several scans.

The first problem is: my plate has "big" dimensions (320 x 280 mm), and so when I turn it to make scans around, the parts without focus get some unrealistic distortions, and this is a problem in shape fusion. See the misalignment of the scans in the picture below:

shape fusion problem.png
Distortions in shape fusion


The second big problem is that the only commom area between the front and rear surface is the thin edge of the plate (2,6 mm!), and so when I try to align front scans with rear scans, the software cannot find a good solution for the alignment. I've tried to use stickers and marks so DAVID could differenciate front surface from rear surface, but even though it cannot align correctely. I've tried also align around Y axis, but it didn't work well, I don't know if I'm doing it right.

Any of you had a similar experience, or perhaps has a tip of how to solve this problem?

Thank you!
Gui
 
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Re: Tricky fusion

Postby Gui » Mon Dec 03, 2012 10:56 am

This is how the real plates look like:

ima.png
Carbon fibre plate
Gui
 
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Re: Tricky fusion

Postby WalterMo » Mon Dec 03, 2012 6:50 pm

You are right, it's difficult to align objects like plates without overlapping areas.

What do you want to demonstrate after manufacturing the carbon fibre plates? I think the flatness of front and rear side and the uniformity of the thickness. So it's not so important to show the edges.

Simply manually align both sides by mouse and fuse them, DAVID will close the gaps. Like I had done it here with the hedgehog for the thread „Challenge of October":
viewtopic.php?p=8986#p8986

Or better you seize on the ideas of Santo when he fused a thin dental prosthesis:
viewtopic.php?f=2&t=1430&p=8983#p8983

Walter
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Re: Tricky fusion

Postby Gui » Wed Dec 05, 2012 9:38 am

Hi Walter, thank you for the reply

Actually for what I want to acomplish, just a scan from one of the surfaces is fine, since the thickness is uniform. Anyway, I spent some time trying to fuse the rear with the front surface, and got curious if someone has done it before and how.

I read the topic from Santo, but didn't understand quite well. What happens when I invert scan normals? It appeared that nothing happened... And what is Poisson fuse?

Thank you!

Gui
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Re: Tricky fusion

Postby VDX » Wed Dec 05, 2012 10:31 am

... for some precise alignments and fusions, that David couldn't do on it's own, I'm prealigning the single scans in another CAD (mostly Lightwave), reimport the prealigned object-file in David and fuse it with closing holes. You can copy/mirror one scan, displace it for the thickness of your plate, flip the normals, so you'll get two sides and fuse it in David.

Did this sort of 'external' mirroring and prealigning with the sea-gull in this thread: viewtopic.php?f=15&t=5220

Viktor
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Re: Tricky fusion

Postby WalterMo » Wed Dec 05, 2012 6:14 pm

Hi Gui,

You can move both scans (rear and front) by mouse to a small parallel distance to each other. This can be done by uploading both in Shape Fusion. To separately move the second one it must be „surrounded“ with a red „cage“. Press the Ctrl key, hold it down and click on the second scan. The cage will appear. As long as Ctrl is pressed you can do (by the mouse) with the second scan whatever you like. If you release it, the mouse will work for both scans.
It's a bit tricky to shift both in a parallel position to each other. If you want to remove the cage, press with the left MB somewhere on a free area of the screen. Or you can toggle with the "cage" between both scans by clicking on the other one. Then fuse.

In former DAVID versions (2.x) we had the possibility to switch-on the triangulated mesh and also the normals. See the screen shots. They show a reduced mesh density. On the magnified image you can detect the normals. If they are inverted they are raised inside the object.

The tool 'Invert normals' is still working by clicking with the right MB on the file name. And so on.

At versions 2.x we had two methods of fusion, Simple and Poisson. Now we only have the better and advanced Poisson method.

Walter
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Bear1.jpg
The mesh at reduced density
Bear2.jpg
Magnified
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