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calibration webcam logitech

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

calibration webcam logitech

Postby tailele » Sun Jul 11, 2010 5:57 pm

Hi boys, i 'm trying to understand if the david is a good condition to scan medium object.In my case i must scan a chair. In this moment i have a logitech 9000 and a green laser with focus. If i have good result, i think to take a ccd camera. but i have some question:
1- when i calibrate the system i see some green line and red cross. But i think to see only red cross...why do i see the green line????
2- are there very much different to logitech webcam and a ccdcamera?for example definition?
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Postby hal » Sun Jul 11, 2010 9:36 pm

Hello tailele,

The green lines are a kind of a "quality feedback" tools: they shown how big is the difference between theoric (perfect condition) and real position of the markers (your calibration). The error value is multiplied x10, so you see better the lines. Now, seems that your green lines are too much big and have different directions. Try to built a better calibration angle and adjust the camera, or the corner, and see better all the markers in the scene (fit better the markers' area with the camera view). But I strongly suggest to use the new V3 set of markers, instead the old sheets (with these, you don't need to see all markers, but only the 6 circles in the center are needed - obviously more circles are visible, more precise will be the calibration).

About cameras: webcams have a CMOS sensor, cameras have CCD sensor. The technology behind is different and the quality too (for more infos, try to search these with Google). But for many purposes, the CMOS are enough. With David you can achieve great results with CMOS sensor. The most important thing is the optics. A webcam don't have a professional optics, and usually the view is quite "wide" and with a "fish eye" distortion. David can compensate very well these lens' problems, but working with good optics, you can scan better and adjust the iris aperture and manually adjust better the focus. An other factor is: usually cheap webcams have plastic lenses. CCD camera use good quality glass lenses.
CCD camera can work with high resolution at higher frame rate than the webcams. For example I use a CCD camera that have 1024x768 resolution at 30 fps. The disadvantage is that you can't change the native resolution. With webcams you can change the resolutions and frame rate. Your Logitech cam can work at higher definition than my CCD camera, but at slower fps and with worse quality of the image (the webcams works with interpolate pixels, CCD don't).

Hope this helps,
Mattia
PC: DELL Alienware 17, Intel I7-4710MQ, 32 Gb Ram, AMD Radeon R9 M290X 4GB.
SO: Win 8.1 64Bit.
CAMs: USB 3.0 CMOS B/N (1280x960, 60 fps).
LENS: 12 mm.
PROJECTOR: DAVID SLS1 ACER K11.
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Re: calibration webcam logitech

Postby tailele » Mon Jul 12, 2010 8:06 am

so, is not the angle perfectly 90 degrees???and in this case the scan cannot be perfect...corret?
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Re: calibration webcam logitech

Postby tailele » Mon Jul 12, 2010 8:48 am

i have a very important question....how can i reduce the stl's dimension file?now the dimension is abou 50 mega; i must arrive to 2 mega...this is very important
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Re: calibration webcam logitech

Postby WalterMo » Mon Jul 12, 2010 9:57 am

Yes, the angle should be exactly 90°. Otherwise it's not possible to align and fuse several scans of an object in best quality.

You can reduce the number of vertices in the 3D window of DAVID Shapefusion:
Load the .obj – File.
Double click on its name with the right mouse button.
Now you will find several tools. Use „Reduce mesh density“.
Under „Properties“ you will find the result.
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Re: calibration webcam logitech

Postby milz » Mon Jul 12, 2010 1:31 pm

hi tailele

tailele wrote:i have a very important question....how can i reduce the stl's dimension file?now the dimension is abou 50 mega; i must arrive to 2 mega...this is very important


Addicted to the main shape of your object you cant reduce the from 50 MB to 2MB without a significant lost of details.
You need to do a retopology by hand.
A good way to reduce the size is to reduce the resolution of the webcam.

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Re: calibration webcam logitech

Postby tailele » Mon Jul 12, 2010 1:35 pm

i have another question. i need this file for a database, so i must be this file in dwg 2d and 3d...so, is it possibile to do this???
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Re: calibration webcam logitech

Postby tailele » Tue Jul 13, 2010 5:47 pm

...all right...i have reduce the mesh without reduce the risolution...with rhino...i have import the obj, then i have reduce te mesh of the 99%...and the scan is absolutly perfect
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