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General / Re: Once again about DEM and 3D accuracy
« on: November 26, 2012, 12:41:12 AM »
Hello Herman, What in your opinion would be the right strategies for corridor mapping? regards
Eduardo
Eduardo
Hello George
I have done a number of practical surveys and have compared results with Totalstation and GPS surveys. The total station and GPS survey was based on the same control points used to fix the ground control points , thus the surveys are inter related.
A few spot checks was done as follows. The survey was draped over the cadastral (legal) boundaries captured independently but related to the same co-ordinate system and it is a perfect match. This being verified by seeing the boundary lines intersect the cairn marking the the boundary beacon or with walls and fences perfectly fitting the boundary layout.
Regarding test done by surveying a GCP but not using it to control the the PS project, results are as follows. In theory I understand that accuracy should be equal to XY=2*GSD and Z=4*GSD. I find it rather to be in the range XY=1*GSD and Z=2*GSD. When testing in relation to a arbitrary spot shot taken , not a physically identifiable point, results are better than XY=2*GSD and Z=4*GSD.
Basic rules of interpolation should be applied and rather too many GCP's.
Also the shape of the project seems to play a roll , long thin project (corridor mapping) is problematic if approached in the wrong way.
Sampling rate has a definite influence on accuracy , but for your standard 25min flight with 500-600 images ,options "smooth" and "high" produce the results above. I fly with an average GSD of 4-5cm.
Regards
Herman
