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Author Topic: When to use camera calibrate function?  (Read 5799 times)

Sky_hie

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When to use camera calibrate function?
« on: September 18, 2014, 01:54:02 PM »
When to use camera calibrate function?

Is there any criteria for when this should be used? And at what stage?


SH
« Last Edit: September 22, 2014, 12:05:00 AM by Sky_hie »

v.vyazovsky@gmail.com

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Re: When to use camera calibrate function?
« Reply #1 on: September 19, 2014, 07:31:50 AM »
I assume it should be used when some of the needed data is missing in exif, which I think won't happen in most cases  with digital cameras and autofocus lens. But with manual lens, for instance, you should set focal length directly in PS in camera calibration dialog.

wastan

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Re: When to use camera calibrate function?
« Reply #2 on: September 19, 2014, 01:04:08 PM »
I assume it should be used when some of the needed data is missing in exif, which I think won't  :-* :D

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Moon

DCK

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Re: When to use camera calibrate function?
« Reply #3 on: September 21, 2014, 01:08:11 AM »
newb question: if I use an automatic lens but set it on manual, is the exif information retained or not?

Patribus

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Re: When to use camera calibrate function?
« Reply #4 on: September 21, 2014, 01:22:09 AM »
There is one thing I do not understand:

I'm using photos without any EXIF content (extracted from video)

I generate my point cloud and set the coordinate system.

When I optimize, isn't the camera settings beeing calibrated at the same time?

Cheers

JMR

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Re: When to use camera calibrate function?
« Reply #5 on: September 21, 2014, 08:36:36 PM »
One could need to calibrate camera in a process apart from the actual scan project when the poor object's texture is expected to deliver very few feature points so it may lead to a weak estimation of lens inner parameters. The same applies to the case an object that fills poorly the frame in most photos of the project, specially near the frame borders.
But it just makes sense if your camera lens setting can be fixed the same for both calibration photo set and photo-scan one. Therefore, precalibration of non-metric cameras is usually unpractical for several reasons: It's sometimes hard to have the calibration pattern with right dimensions to be shot at the same distance as the actual object. If the calibration board/screen is not available during the scan photo session and viceversa, its likely to happen changes in lens parameters in the meanwhile. Most p&s cameras and also many dslr lenses lack of the desirable mechanical stability, and lens parameters may change significantly in spite of any care when you shut down the camera, go to somewhere else and then turn on again.

David Cockey

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Re: When to use camera calibrate function?
« Reply #6 on: September 22, 2014, 05:36:26 AM »
newb question: if I use an automatic lens but set it on manual, is the exif information retained or not?
What camera and lens?  Automatic focus, automatic exposure or something else?

Both my Canon cameras always write EXIF information to the image files.

nj

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Re: When to use camera calibrate function?
« Reply #7 on: September 22, 2014, 03:25:26 PM »
When to use camera calibrate function?
Is there any criteria for when this should be used? And at what stage?

certain scenarios will require camera calibration.
recently i tested a mirror-less system with a zoom-lens, fixed @ the max. fov.
i took about 10 photos of a flat, well textured brick-wall. camera-orientation close to the normal case, like in aerial or stereo photogrammetry.

the reconstuction without pre-calibration resulted in a (barrel-like) distorted model. the wall was bent. the reconstruction with data from calibration resulted in an accurate model.
there are many articles out there, examinating the process of self-calibration.
like cahngchang wu's paper: Critical Configurations For Radial Distortion Self-Calibration http://ccwu.me/file/radial.pdf or a german publication presenting charts of deviation of parameters from self-calibration vs. calibrated data. https://www.hcu-hamburg.de/fileadmin/documents/Geomatik/Labor_Photo/publik/dvw_schriftenreihe_tls2012_remondino_kersten.pdf

you should apply the calibration-profile before you start image alignment.

Sky_hie

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Re: When to use camera calibrate function?
« Reply #8 on: September 22, 2014, 04:09:18 PM »
When to use camera calibrate function?
Is there any criteria for when this should be used? And at what stage?

certain scenarios will require camera calibration.
recently i tested a mirror-less system with a zoom-lens, fixed @ the max. fov.
i took about 10 photos of a flat, well textured brick-wall. camera-orientation close to the normal case, like in aerial or stereo photogrammetry.

the reconstuction without pre-calibration resulted in a (barrel-like) distorted model. the wall was bent. the reconstruction with data from calibration resulted in an accurate model.
there are many articles out there, examinating the process of self-calibration.
like cahngchang wu's paper: Critical Configurations For Radial Distortion Self-Calibration http://ccwu.me/file/radial.pdf or a german publication presenting charts of deviation of parameters from self-calibration vs. calibrated data. https://www.hcu-hamburg.de/fileadmin/documents/Geomatik/Labor_Photo/publik/dvw_schriftenreihe_tls2012_remondino_kersten.pdf

you should apply the calibration-profile before you start image alignment.

Thank you for Your answer. I have actually Applied the calibration before image alignment.

SH