Orthophoto Distortion

[UAV_Survey]

I am having problems processing a project using Agisoft Photoscan Pro. The project is an industrial complex with some tall structures and some overhead pipework. The photography was acquired using a fixed-wing UAV – 1000 images with a 85% forward and 65% lateral overlap. The project has about 20 ground control points and there were no problems with the alignment or mesh generation.

I am having problems with distortion in the orthophoto, please see attached example of raw image and orthophoto extract. I am aware that these types of objects cause problems for Agisoft, but is there a way to minimise this distortion?

Links to original image sample and processed orthophoto

http://tinypic.com/r/qmz7v5/5  Raw image

http://tinypic.com/r/ncjqja/5  Orthophoto

Thanks

[RalfH]

Orthophotos for such complicated structures can be very tricky. Usually the approach for orthophotos in Photoscan is to use a lower-resolution mesh for orthophoto generation to reduce memory load and processing time. For complicated structures, that approach will result in some texture being mapped in the wrong places, causing distortions. Perhaps that's what happened in your case; hard to tell without knowing your processing settings. Another reason (if you used high or ultra quality mesh for orthophoto generation) could be that camera alignment or calibration were suboptimal. In that case, make sure you use separate camera calibration setting.

As an alternative to orthophoto generation in Photoscan, you could export the dense point cloud at ultra quality and create a colour map from that to see if the problems persist.

[UAV_Survey]

Ralf,

Thanks for you reply. I have processed the data using a variety of settings but none give a reasonable result.

Typical settings

Alignment - Medium
Model  - 18 million faces, Height field, Smooth, Medium
Texture - Orthophoto, Mosaic, Atlas 8000 x 8000

I have also tested a smaller section of the site at High alignment, Ultra High mesh with the same poor results

[bisenberger]

You might try Sharp instead of Smooth. This will probably leave some holes in the mesh to be filled, but it is likely to remove some of that distortion.

[RalfH]

Yes, for complicated structures "sharp" should be better. Also, use depth filter setting "mild" ("aggressive" removes many points whose distance from the camera differs stongly from that of the surrounding points).

[UAV_Survey]

Ralf,

Where can I find the option for Mild Depth Filter? I am using Version 0.9.0 Build1586.

Thanks

[RalfH]

Tools >> Preferences >> General >> Model Generation >> Depth Filtering