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Topics - bgt051@mun.ca

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General / DEM Accuracy Issues
« on: August 31, 2020, 09:33:58 PM »
Hi all,

I am having issues with my DEM's. I've read a few other posts somewhat similar to my situation but being very new to this field and software I am still confused.


I have collected aerial imagery data repeatedly from the exact same coastal beach location because I want to observe the elevation changes over time. Through flight planning software I've collected hundreds of vertical photos, the first survey flown at 60m and the rest at 40m. However, after following the workflow process to build DEMs for each visit to the location I find some differences between them to be greater than 30m (~100'). Locations on the DEM that I know to be impossible to have changed at all over my study period show changes of over 30cm (1').


I used 13 GCP over a span of <0.1 kmĀ² (25 acres), two of which I unchecked during processing in Metashape for the purpose of accuracy checkpoints. I have re-checked my GNSS data and have not observed any major errors with any of my GCPs.

I have noticed that water behaves very funny. For images I captured that was all water, Metashape fails to align those photos and remained unselected for the rest of the workflow. However, for the photos that are directly along the coastline and are able to align, does the water in these images create interpolation issues for the remained of the map?

Any help/suggestions would be greatly appreciated. I will be glad to elaborate/clarify anything to help lead to a solution.


Thanks,


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