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Author Topic: Median orthomosaic blending option  (Read 756 times)

wgreenePIMS

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Median orthomosaic blending option
« on: March 21, 2023, 07:38:15 PM »
Hi Alexey,

I have a question related to orthomosaic blending. In the vast majority of cases, using mosaic or average is suitable, but there are certain situations that I run into frequently doing multispectral drone surveys of coral reefs where there are very significant outlier images, where waves or sunglint completely blows out some pixel values. The average blending mode works well to iron out some of these issues, but in certain locations where there are more frequent issues (crashing waves on a shallow patch of reef, for example), average leads to unusable results, even though there clearly are plenty of images in the area that provide excellent source data for those pixels. Attached is an example of the problems introduced by average blending in crashing wave areas.

I think a median blending or a weighted average mode would work far better in some cases, so that outlier values do not affect the results. Is there any way to do this via python scripting or is there potential to include an additional blending mode in the orthomosaicking step? A median blending mode would seem to be just as computationally easy as average. I know it is currently possible to export orthophotos and blend them in other GIS software using more complex blending options, but this workaround is tedious and very time consuming.

I've also found that the traditional method of drawing a polygon and assigning images on the ortho itself does not work while using average blending - you are allowed to make multi-selections as usual, but when updating the orthomosaic, nothing changes. If this could be fixed, it would at least help solve the problem significantly by being able to manually exclude some images from the average blending in specific areas.

As always, thanks for the excellent help with all of our questions!