Roof problem

[Paul17]

Hello,

I've recently been trialling Metashape and have used my DJI Mini 2 to capture a typical scenario.  However I'm having some trouble with one of the roofs in the scene. This roof is higher than all the others which I think might be part of the problem. 

I have:

• Tried using DNG's rather than the JPG's
• Tried various levels of cloud density
• Tried the 3 different depth filtering values Mild/Moderate/Aggressive
• Tried manually aligning the photos from along the ridge of the roof with hundreds of tie points
• Tried a chessboard camera calibration

Unfortunately nothing seems to fix it.  The photos taken above the ridge of the roof seem sharp and clear, and Metashape has no problem aligning them. Please see attached images.

Any help or advice would be greatly appreciated!

Many thanks,
Paul

[dpitman]

What was your overlap settings and how tall are the buildings?  As you suspect, tall objects do not get as much overlap as the surface.  Also, homogenious surface like grass, trees and roofing material require even more overlap.

Take a look at "dense cloud confidence".  Lower confidence results from not enough overlap.

[Paul17]

Thanks for your reply,

I took off from a flat roof which was about the same height as the average height of the roofs. I set the altitude to 15M with a front and side overlap of 75%.  From looking at the photos manually I do seem to have achieved this over most of the scene, however at the peak roof height (which I think was about 5M below the drone) it falls to 40% sidelap and 50% frontlap. This is roughly what I estimated as I assumed this would still work out OK for producing a 2.5D orthomosaic.

I have re-run the dense cloud with "Calculate point confidence" turned on and have filtered the dense cloud by confidence. As I increase the minimum confidence, lower parts of the roof do start disappearing, so I presume this does mean it's an overlap problem?

If so, the next step would be to re-fly over the roof a bit higher and ensuring more overlap? And then I could re-insert those photos into the project and mask out any ground areas where things may have changed?

Many thanks again for your help!

Paul