[OpenDroneMap-users] processing undistorted Go Pro imagery

[Alex Mandel]

Please see previous posts on this topic in the mailing list archive.
http://osgeo-org.1560.x6.nabble.com/OpenDroneMap-f5186282.html

So far my analysis is that the focal length stays the same.
Experimentally if your removal of distortion is like my scripts, then
you lose approximately 20-25% of the width of the sensor. I calculated
this from taking pictures of a checkerboard pattern and counting the
squares lost.

The Exif tag just has to match what you put in the ccd_json file.

FYI, I highly recommend you fly gopro's in time interval mode, video
mode produces a much lower resolution output.

Thanks,
Alex

On 04/16/2015 02:53 PM, Aaron Dennis wrote:
> Hello,
> 
> I've seen some incredible output from example datasets with OpenDroneMap.
> 
> Right now, I'm working with some researchers who fly a UAS with a GoPro
> Hero 3+ Silver camera to collect video. I'm trying to pull image frames
> from that video, remove the fisheye distortion, and run the images through
> OpenDroneMap.
> 
> I pull frames from the video with this command:
> 
> $ ffmpeg -i video.mp4 -r 1 %03d.jpg
> 
> Then, what I've been doing is removing barrel distortion (fish eye) from
> the images with $ imagemagick:
> 
> convert image.jpg -distort barrel '0.030530 -0.124312 -0.038543'
> corrected_image.jpg
> 
> I also add exif tags to the imagery using exiftool:
> 
> $ exiftool -make=Gopro corrected_image.jpg
> $ exiftool -model=HD3 corrected_image.jpg
> $ exiftool -FocalLength="2.8 mm" corrected_image.jpg
> 
> My challenge now is determining if 2.88 mm is still the correct exif tag
> for the image, having already successfully removed distortion. Also, I'm
> not sure how this will affect the sensor size in ccd_defs.json. I've tried
> running the images through OpenDroneMap both distorted and undistorted
> using the exif tags shown above, and each time I end up with an empty point
> cloud.
> 
> Matching key points appeared to go okay.
> 
>    14151 matches (23.8%) took  6.63s for
> /home/ubuntu/images/reconstruction-with-image-size-2400/matches/0-1.txt
> ...........
> 
>    14093 matches (23.7%) took  6.93s for
> /home/ubuntu/images/reconstruction-with-image-size-2400/matches/0-2.txt .
> 
>     1670 matches ( 2.8%) took  6.94s for
> /home/ubuntu/images/reconstruction-with-image-size-2400/matches/0-3.txt
> ...............................
> 
>    17644 matches (28.4%) took  7.22s for
> /home/ubuntu/images/reconstruction-with-image-size-2400/matches/1-2.txt .
> 
>     1762 matches ( 2.8%) took  7.20s for
> /home/ubuntu/images/reconstruction-with-image-size-2400/matches/1-3.txt
> .........................................
> 
>     1901 matches ( 3.0%) took  7.18s for
> /home/ubuntu/images/reconstruction-with-image-size-2400/matches/2-3.txt
> 
> But running pmvs seemed to maybe filter out all those key points? Running
> meshing returned an error that the point cloud was empty.
> 
> I was wondering if anyone has a solution to processing Go Pro imagery or
> video or if anyone has some ideas about what focal length or CCD size would
> be appropriate for undistorted imagery.
> 
> Thanks,
> Aaron
> 
> 
> *Aaron Dennis*
> aaron.p.dennis at gmail.com
> 
> 
> 
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