I have a 40-acre field that I would like to map every week using the same flight path. The flight last week went great and Agisoft stitched and processed all pictures with great results (around 250 pictures). Yesterday I do the exact same flight with the same number of pictures, and Agisoft can barely stitch half of them.

For last week's flight it reported an average altitude of 110 m (it was actually 100 m). But for the pictures that Agisoft was able to stitch it claims that the altitude is 80 m when it was really again 100 m.

What went wrong? I didn't do anything differently. Like I said, same flight path, same camera settings, same processing options. Any ideas are welcome.

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Some things to check:

- was the camera zoomed in? That could reduce your overlap.

- what is the quality of the images, are they heavily blurred?

- not sure if agisoft relies on having GPS positions in the exif to do some kind of initial matching. Check if the positions are there (could be a step that was forgotten too). 

- what is the exposure for the pictures, are they all about the same?  Not all feature matching algorithms can deal with differences in exposure. Could have an impact too because of cloud cover conditions.

- if the gps positions in the pictures are completely wrong, then perhaps the radius it considers to match with other photos is off. Then you could try another initial matching method (or match every picture against the other) to see if that improves results.

Thanks for the suggestions.

Hi Tom,

I do similar collections with an IRIS+ and GoPro combination and have not seen Photoscan make this type of error.  The errors you quote on the altitude are very large (10-20m).  With my IRIS+/GoPro I generally see errors of less than 3m after initial alignment. Gerard had some good suggestions.  A couple more I might offer:

1.  What type of camera are you using? If it has a fisheye lens (GoPro or DJI Phantom 2 Vision or Vision+) then make sure you have fisheye selected under the Camera Calibration settings.  Given your large estimated errors it may be that the calculated calibration coefficients have gone all wonky on you.   This can happen if you have a fisheye lens camera and are processing as a frame camera.  

2.  What version of Photoscan are you using?  I spoke recently with the developers and they said that in the newest version they are now using the camera positions a bit differently during alignment.  If the positions are actually off as much as you say, then they may not be aligning because of this.   Under the reference settings you can change the expected camera accuracy.  Not sure this will fix it, but worth a try.  

3.  Based on Gerard's first suggestion is to visually verify that you have sufficient overlap and sidelap for processing.  You should be able to do this pretty easily just by scanning through the images. It may save you from chasing other things if for some reason you have gaps that Photoscan can't process across.  

Hope it works out for you.  I am troubled by the altitude errors.  Those are pretty large.  

Scott

Not sure why I called you Tom.  Sorry Eric.  

Off topic but what benefit is it to collect such data weekly? What are you observing.?

Plant growth.

I would tighten the flight path. Or fly 2 laps of the flight path. I combined the pictures from 3 flights and got good results.To get more overlap I was thinking of using 2 cameras mounted on the ends of a 6 ft boom. The cameras don't have to be synchronized. It's just an idea but I think it might require identical cameras with the same settings.

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