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Messages - Guy Byrne

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General / Re: Problem aligning images and gcps
« on: August 07, 2020, 04:01:10 AM »
Thank you Paul!

That thread : Point cloud / Ortho are skewed/tilted (no GCPs)  gives me a lot to work with ..  I'll post an update later.

kind regards

Guy 

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General / Problem aligning images and gcps
« on: August 06, 2020, 07:23:12 AM »
Dear Forum,

I'm still on trainer wheels with metashape (v1.6) but after dozens of iterations to troubleshoot a problem ... i think i need some advice.

I have faithfully followed the  Agisoft 'Tutorial for beginners: Orthophoto and DEM generation (with GCPs) ..' and a number of (excellent) video tutorials by SkySurv.


My test data set comprises imagery captured with a dji mavic pro ... and a web of rtk GCP,s captured using an altus aps3g base/rover gps.  The photography have 80% forward and side overlap, is I assume in wgs84 .  Flying height was ~30m above ground on a perfect day with little or no breeze.  The GCP's are in GDA/94  UTMS (zone 55) (SE Australia).


Briefly i can get a very good result if i use a small subset of my photos (76) and the GCPs (6) - but when I try and emulate the workflow with my whole data set (280 photos and 15 gcp's)  I can't get a usable solution. 

The first manifestation things are array is after i align the 280 photos ..  there is an east west offset (about 27m) in the 'cameras' and the sparse point cloud.   When I bring in the GCP's that offset persists.

I have tried both transforming the imagery to GDA and also leaving it in wgs84, i have also tried explicitly defining the different image and gcp coordinate spaces.

I can import my gcps as a kml into google earth and they align perfectly .. so i think the error is coming from the photography.
 
I have attached 4 images that i hope explain the problem. 1) a nadir view of the basic camera model, 2)  screen view of the gcp import window, 3) ortho view of the gcp markers and the cameras (is a sensible relationship), 4 ) the camera's and gcp's atop the cloud with the 27m offset shown

thanks in advance

Guy Byrne
(Geoscience Australia)


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