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Author Topic: Avoiding banana shaped walls (bad distortion correction from GoPro camera)  (Read 3789 times)

basilio

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Hello everyone!

We're trying to reconstruct a very detailed and textured wall, filmed from a gopro while walking alongside it. The reconstruction works very well (at least in terms of relative positioning of the cameras) but the flat wall is now a banana.

My guess is that the distortion correction from the very wide-angled gopro has not worked out properly. The images have no exif data as they were extracted from the mp4 video (via ffmpeg) so I imagine that the software has to start from scratch in terms of estimating camera distortion, and it's not able to measure how badly distorted it is.

Is there some magical options that I'm completely missing and that would solve my problem?

Thanks!

basilio

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Re: Avoiding banana shaped walls (bad distortion correction from GoPro camera)
« Reply #1 on: December 02, 2015, 04:17:18 PM »
After recovering the source video and getting the frames at a higher resolution (for some reason it was downsized while exporting) the software is able to better estimate the lens distortion and the result is much less bended!

So that solves my immediate problem, but if I hadnt had access to the higher res images, would there have been someway to improve it?

Kiesel

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Re: Avoiding banana shaped walls (bad distortion correction from GoPro camera)
« Reply #2 on: December 02, 2015, 06:31:16 PM »
In short:

1. the gopro has a fisheye lens, so you have to set the lens type in camera calibration to fisheye.
2. you can start your line with a image sequence for camera calibration (take pictures in different heights and angles of one part of your object. You can even mix horizontal and vertical pictures)
3. avoid single lines, better are at least two lines in different heights.

Karsten

basilio

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Re: Avoiding banana shaped walls (bad distortion correction from GoPro camera)
« Reply #3 on: December 02, 2015, 08:02:51 PM »
Dear Kiesel,

Thanks a lot! The first point is definitely what I was missing! Regarding 2. and 3. indeed that would be best, but unfortunately the people I send on the field are not trained to take pictures, so "Point the GoPro at the wall while you walk by it" is about as far as the complexity of the task can be.

Nevertheless it's very useful insight!

Kiesel

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Re: Avoiding banana shaped walls (bad distortion correction from GoPro camera)
« Reply #4 on: December 02, 2015, 11:15:35 PM »
You can do the camera calibration for the GoPro ones (for same conditions) and import the calibration data in your actual job and fix it.  :)

bigben

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Re: Avoiding banana shaped walls (bad distortion correction from GoPro camera)
« Reply #5 on: December 04, 2015, 12:59:20 PM »
And shoot time lapse, not video. 0.5 sec per frame and walk slowly.  then you have 12mp images.  Samsung nx3000 and 10mm lens would be even better for the money