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DAVID-Laserscanner Forum • View topic - define center of rotation
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define center of rotation

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

define center of rotation

Postby Erik78 » Sat Mar 06, 2010 5:31 pm

Hello everybody,
I want to check if it is possible to get very precise 360° scanns (I want to check the accuracy of the scan data with Geomagic Qualify). To minimize the mistakes which are done by automatic alignment I want to rotate them with a turntable by a defined angle.
As I read in the forum is the center of rotation which is used in Shapefusion at the corner of the two calibration boards.
Now my question:

Is it possible to define the rotation center anywhere in front of the calibration boards, to put the center of the turntable on this new rotation center. That would be great !!!

Thank you very much.
Erik
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Re: define center of rotation

Postby MagWeb » Sat Mar 06, 2010 6:13 pm

Hi,


You can define the background structure and the calibration planes with some offset to the origin in the advanced settings instead :wink:

Gunter

Edit:

but it's hard to get the the corner's edge parralel to a rotaion axis accurately
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Re: define center of rotation

Postby Erik78 » Sat Mar 06, 2010 7:08 pm

Hi Gunter,
thanks for your fast answer. :D
Whrere in the advanced settings is it possible to change these values, or rather which values have to be changed ? What is the unit of these values? I already tried this, but the software says that the left and the right side of the backround is not in the same plane.

I also tried to scan without backround ...but the result was very bad ...I´m scanning with a stepper motor. Have you maby got experiences with this scanning method? Is it possible to get the same results than with backround ?


Thank you very much
Erik
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Re: define center of rotation

Postby MagWeb » Sat Mar 06, 2010 10:19 pm

Hi,

the attached images show how to set the offset using the new calibration patterns V3. Dimensions are mm and this example assumes a turntable of 200mm diameter.
If you use the old patterns, instead of setting the values in LeftCalibrationPattern and RightCalibrationPattern you´ve to modify the calibpoints.dat file values (to open in the Editor).
(you´ve to subtract 100 from the values of the 2nd and 4th column, also if there´s a zero).

Scanning without a background you can get ( nearly) the same result as with planes if all is right. That needs an accurate repeatable motion starting at exactly the same position and a precise corner to do the reference scan. If that is guaranteed you may get even better results for your camsettings can be concentrated only on the objects needs.

Gunter
Attachments
Offset.jpg
Offset2.jpg
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Re: define center of rotation

Postby MagWeb » Sun Mar 07, 2010 12:13 am

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Re: define center of rotation

Postby Sven » Sun Mar 07, 2010 11:25 am

Hello Erik,
Gunter is right: It is not necessary to define the offset in X and Z. It does not help in the alignment at all. If you choose "Rotation around Y only", Shapefusion will still move in X and Z automatically. So if I understand right what you want to do, you don't need to change any Advanced Settings.
Afterwards you should apply Fine Registration and/or Global Fine Registration.
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Re: define center of rotation

Postby Erik78 » Sun Mar 07, 2010 4:37 pm

Thanks for your replies.

I have a very precise turntable which I want to use. My idea is to turn off all automatic features in shapefusion and rotate the object only by a known angle around the the center of the turntable (which I want to define in Shapefusion) to match the object. Is there no possibility to turn the other features off? My aim is an accurate analysis according to VDI / VDE 2634 "Optical 3-D measuring systems Optical systems based on area scanning" that means I need to keep the error in matching at a minimum or rather “zero”. With fine registration etc. in shapefusion the object is matched to vague for this porpose.

Maybe you can help me.
Thanks for your efforts, that´s very kind of you.
Erik
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Re: define center of rotation

Postby Bongobat » Sun Mar 07, 2010 4:54 pm

Hi,

Just a thought. Can you accurately place a pole or plane that goes through your turntable center? You could calibrate your camera and scan this pole and save the file. Without changing anything except removing the pole place your object center aligned with turntable center and make your scans. Now go into your 3d software and import the turntable pole scan and your object scans. Move the objects transformation/rotation axis (not the object just the axis) to the location of the pole. Now when you rotate the objects in 3d with the exact angles your physical turntable rotated the scans should match up.

To do this in David I think we need a few new features in the 3D window:
A way to define or move the translation/rotation axis of the scan.
A way to input numerical translation/rotation values for each object (scan).

Greg
DealExtreme red line laser, Microsoft Lifecam HD-5000
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Re: define center of rotation

Postby funtasma » Mon Mar 08, 2010 12:01 pm

I agree with Erik, it would be extremely helpful to have the axis of the turntable defined and then use the known angles in shapefusion to automate the alignment process. this would be super fast and precise.

My idea to define the axis is to use a calibration mat with acalibration pattern for the turntable. All it needs is a series of let us say eight pictures - every 45°. With those pictures of the different angles of the turning table it would be possible to exactly define the position of the axis (x,y and z).

-Benjamin-
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Re: define center of rotation

Postby funtasma » Thu Mar 11, 2010 11:28 am

I just wanted to show what I mean. This picture is from a series of photos which I used to test a photo based 3D-"scanning"-software. With this kind of calibration mat they determine the x, y and z position of the object in relation to the camera. This would work for David as well to find the center and angle of the turntables axis.

-Benjamin-

P.S.:The scans of the software I mentioned are by quality not compareable to DAVIDs detailed results.

Screenshot_341.jpg
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Re: define center of rotation

Postby cassey37 » Thu Sep 22, 2011 1:28 pm

Thanks for letting me know about other good stuff! :wink:
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