[need help] Shadows of "Flight Grid" in the final Orthomosaic

PIX4Dmapper PIX4Dmapper Questions/Troubleshooting
1

Hello,

I did several larger Project lately and recognized, that in all of them the final Orthomosaics show “shadows” exactly in the Flight direction, so that you can see the grid the drone was flying. Normaly I do small projects and so far everything went right without any problems, bu now I think I need some help :slight_smile:

The Projects was made with a 75% overlap on both sides (front and side) and a DJI Pjantom 3 Pro was used to take the pictures at 80m above ground.

What did I do wrong or what can I do to avoid the shadows ? By just looking at the pictures everything is fine, and if you zoom far enough you can not see the shadows at all … Is there a way to “safe” the projects ? 

I appreciate any help … thanks in advance.

 

 

 

 

2

Hey Ralf,

It looks like you have a significant number of images that have shadows/brigh-dark spots and some with the sun spots. Was it patchy clouds when you flew it? One thing you could do would be identifying those images then remove them and re-process however judging by looking at your orthomosaic it looks like it is covering the whole thing so if you remove those images you would end up with holes in your orthomosaic.

3

Hello Selim,

Thanks for your quick response !

Yes it is more or less covering the whole thing, so it looks like it is a systematic “error”.

It took quit some time to fly, but it was a sunny day with only a few clouds and judging that the shadows align the Fly Grid, I don’t think that is has something to do with clouds, It would be strange if the clouds would align the flying grid :slight_smile:

What me suprises is, that the colorized dense Pointcloud don’t show these shadows at all … If the Orthophotos looked like the clorized dense pointcloud evrything would be fine …

 

4

I regularly see this problem in Orthomosaics constructed from multirotor missions (especially when using consumer cameras) (a multirotor will always tilt up in the direction of flight). I believe it has a lot to do with the direction of sunlight relative to the drone (it is greatly reduced by always flying flight legs in the same direction, something which is not feasible for most flights due to battery limitations). This effect is usually corrected for in the reflectance maps, although I’ve noticed that in recent versions of pix4dmapper, this correction is not working as well.

Perhaps otehr can advise in color balancing or other settings that may be used to reduce the effect. The use of color modification is risky for those of us wanting to create vegetable index maps, but may not be a problem for those wanting to get a nicel looking RGB image.

5

Hey Ralf,

I had couple project before the clouds were aligning with the flying grids and removing the images in those flight lines actually fixed the issue, but it was in smaller regions. What processing settings have you used for image scale and calibration method? 

Moreover as far as I know the colour balancing should be applied automatically for RGB images in Pix4D. I wouldn’t try to perform a manual color correction for Multi-spectral images as Dvoralai mentioned above it could affect the reflectance values. 

6

Thanks again for your responses, I really apprechiate any help !

What I found out so far, is that there is no way for me, that Pix4D “fix” this problem for me with the same Input Images.

There is no other way for me than fly again on a really cloudy day without sun and diffuse light :slight_smile: Unfortunately I don’t have this option, so I use the dense Pointcloud (wihch don’t show these shadows at all) and the DEM, which is allright.

I had to remove the shadows on the orthophotos with Lightroom by hand :slight_smile: … The accuracy seems to be good enough so far and the effect is only visible in smaller scales … I hope my skills in image editing are good enough :slight_smile:

Thanks again for your help

 

Regards

Ralf

 

7

Hey Ralf,

I am glad you found a work-around. Removing the shadows manually seems like a difficult task.