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Checking Calibration

The place for questions, problems, comments and tips regarding the camera calibration.

Checking Calibration

Postby MagWeb » Sun Jan 27, 2008 10:02 pm

Hello Davidians,

with the posibility to scan DAVID'S corner with unabled backgroundfilter we have an ideal tool to check and compare the precision of our setups:
You can download and read about this version, Sven kindly posted, here
http://www.david-laserscanner.com/forum/viewtopic.php?t=351

Simply scan your empty corner !

The scanresult in 3D view should match exactly to the grid, that is shown in DAVID'S 3D viewer.

You easily can see deformations and if necessary you can react in changing the positioning of your patterns - we didn´t have such a visual check (the same for every user) before.

I did some tests today with my system of removable patternboards. I added 4 screws to adjust the boards, and could quickly improve my calibration to the status, that the grid is visible from both sides of the scan all over the planes. This should be the ideal.

I noticed that it is VERY important to spread the calibpattern all over the campicture. So I used a distorted pattern discribed in:
http://www.david-laserscanner.com/forum/viewtopic.php?t=242

Gunter
Attachments
testsetup.jpg
Basics of my results
perfect.jpg
The ideal: intersection of grid and scanresult all over the scanned planes
Patternsizes.jpg
Comparing different zoom factors at the same pattern target, and its calibration result.
MagWeb
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Re: Checking Calibration

Postby Patrick » Wed Nov 04, 2009 3:58 am

Is there a way to extend the 'grid' in David to a window scanning system to make use of Gunter's alignment check?

Thanks.

Pat
Pat
Patrick
 
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Location: Canada

Re: Checking Calibration

Postby Khalid Khattak » Fri Nov 06, 2009 7:46 am

Patrick, very nice question.. I afraid we have no tool to extend the grid in the David.. May be Sven/Simon can check it in new updates..
PC: Dell Inspiron i3, 2.27GHz,4GB RAM,64 bit windows 7
CAMERA:
David CCD Mono USB
LASER:
David 5mW Green line laser
PROJECTOR:
3D LED Mini Projector 250lumens, Native 1024x600
[b]http://free3dscans.blogspot.com/
Khalid Khattak
 
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Location: Pakistan

Re: Checking Calibration

Postby Sven » Fri Nov 06, 2009 9:47 am

No, there is no way to increase that grid's size at this time.

I have created two perfect large panels (1000*1000 mm) as OBJ (see attached baseplanes.obj), you can load them in Shapefusion together with your scan of the background planes, and compare them there.
You can easily change the size by editing baseplanes.obj with a text editor and replacing all "1000" by another number.
Hope that helps you.

Sven
Attachments
baseplanes.obj
(138 Bytes) Downloaded 259 times
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Sven
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Re: Checking Calibration

Postby Khalid Khattak » Fri Nov 06, 2009 5:04 pm

Sven, Thats a great Make-shift short term solution... :) Thanks for helping us and i know something great going behind the scene,,.. You guys are working very fast... I am happy with two Companys with great solutions with low-cost high quality products.. One is the Vectric and the Second is DAvid Laser Scanner..

Regards
PC: Dell Inspiron i3, 2.27GHz,4GB RAM,64 bit windows 7
CAMERA:
David CCD Mono USB
LASER:
David 5mW Green line laser
PROJECTOR:
3D LED Mini Projector 250lumens, Native 1024x600
[b]http://free3dscans.blogspot.com/
Khalid Khattak
 
Posts: 942
Joined: Thu Apr 23, 2009 1:30 pm
Location: Pakistan

Re: Checking Calibration

Postby Patrick » Sat Nov 07, 2009 1:47 am

Sven,

Thanks.
That does help a lot.

I have a fairly large window system that we have been building and rebuilding over time.
1.5 m long panels, 280mm wide and a 1.3 m opening.

We use it to scan the surface of damaged heavy plates. It is a great way to quickly characterize the large number of dents on each plate.

What has been a long standing problem is the amount of distortion:
Scan from 'above' the camera does not match scan from 'below' the camera. we need both directions to illuminate both sides of each dent.
I have followed much of the advice on this forum (many thanks to everyone).
We are using a flavour of Magweb's expanded calibration pattern (left side columns spaced).
Calibration is placed on the panels using adhesive 'dots' laid onto cross hair reference lines (with the .dat file updated accordingly.
Green, focusable laser and a Logitech Quickcam Pro for notebook.

I can check and re-check all the parameters but now with you little 'ideal' corner, I can see how the reference panels match up.
left1-vs-ideal.jpg
left panel versus ideal corner - below camera
left2-vs-ideal.jpg
left panel versus ideal corner - above camera


I can see they are not perfect but is this what is giving me my distortion and misalignment (about 12mm over 1200)?
Or are there other parameters I am missing.

Thanks.
Pat
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Location: Canada


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