fixing uncalibrated images dense vegetation

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

ok I have to make map with boundaries on it. As you can see I have some swaths of Red. So trying to see best way to fix that. I can refly those areas but if I do I want to make sure I do it correct and know for future. So this was 200 acres in valley with flanking hills. Elevation from top to bottom is like 400’ difference. So I flew the flight at 200 above GSL. If I few at one elevation the lower elevation detail would be terrible. I also did my photos by distance not timed.

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image1301×1290 293 KB

So just trying to see how I can clean up the red either with processing or refly those areas again with different settings ?

Uploaded Quality Report after step 2 also.

so ultimate questions are.
Ok to fly 200’ above ground level or should I do set altitude ?
should I do timed interval or distance
should I fly the red again or do some manual tie points or something else post processing?

Any suggestions to make better on this one and future are welcome.

Note: this is partial job, need to return to fly bottom 1/4 of area still and my RTK was working start of each flight then went out… so pretty much only GPS no RTK.

Thanks
StLawBoroTop_report.pdf (1.3 MB)

1 Like
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Hi Kevin,
Dense vegetation is notoriously difficult to map. It has a complex geometry that can move in the wind. As a result, it can be difficult to generate a sufficient amount of keypoints. You will want to fly as high as you can with very high overlap. Possibly in the 80-85% range.

For this project, you can try dropping the image scale under step 1 down to 1/2 or perhaps 1/4. This will tend to negate the effects of the vegetation. I would also use the Alternative Calibration Method. This should help.

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I can try those things. Just want some clarification on outcomes if I do.

So if I fly higher, I assume that will affect the quality of the map correct. Less finer detail ?
I assume the image scale downplay would do the same thing ?

I flew at 200’ because I wanted the map to be high quality so the client could pick out objects in the map, see things clearly. I assume when I do that, it has its own side effects.

I was thinking of going to the red area’s and take some temp paint and drawl on some rocks so then there would be easy items for it to calibrate on. Then fly that area again.

Thanks for the info, and if you have answers to my follow ups.

4

Yes, there is a direct relationship between your flight height and your ground sampling distance (GSD). The higher you fly, the larger your GSD.

However, the average GSD value is calculated based on the altitude of the flight and the camera model (resolution, focal length, etc). Therefore the GSD value is not directly affected by the Keypoints Image Scale value used in the Initial Processing.

It is a delicate balance with vegetation, as a lower image scale will usually result in a slightly reduced accuracy because fewer features will be extracted. However, the tradeoff is that it usually results in better outputs (more calibrated cameras) than the full scale for such images. Ultimately, the best approach for vegetation is to fly with very high overlap and as high as possible.

5

Thanks Mike.

So one more question… so now I’m thinking do 300’ with 85% overlap… think I’m at 220’ with 80% now… but…
do you suggest follow terrain ? this location is small valley, with 200’ difference from floor to hill…
if I do 300’ off top elevation I’ll be 500 up and not good accuracy at that height I assume?

6

Yes, I absolutely recommend using terrain follow. It will keep your GSD and your overlap constant. The overall quality will be much better.