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Author Topic: Slight rotation in referenced model  (Read 2216 times)

jl

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Slight rotation in referenced model
« on: May 11, 2015, 10:51:23 PM »
Many of the models we generate have a small rotation component to them.  I've attached a colorized DEM as an example - the ground (and especially the roof) is actually flat throughout the entire image.  I can't tell if this is due to drift in the GPS coordinates during the flight, the camera not pointing exactly straight down, or something else.  Any insight into the problem?

Patribus

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Re: Slight rotation in referenced model
« Reply #1 on: May 11, 2015, 11:11:26 PM »
Hello,

did you also use ground control points? Which drone do you use?

I have had similar issues. In some cases I was aware about the reason, in some other cases not really.

One reason I found out was related to the geo-referencing of the images. Due to missing geo-tags (already one is enough) the tagging of the photos using the software of my drone company interpolated the geo value for all other photos, so there was a slight shift, which however led to shifts or slight rotations of the model.  But this was more than 1 year ago and the geo-tagging process was improved.

Nevertheless, in my last work, I see also a shift and slight rotation of the final model, although the error should be smaller according to the results of PS. I'm not able to understand this and I will write to my drone company to ask about possible connections to the GPS values of the drone.

I'll let you know if I find something out.

jl

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Re: Slight rotation in referenced model
« Reply #2 on: May 12, 2015, 12:19:58 AM »
No, I'm not using GCPs.  The source georeferencing on the images is very good (usually < .2 meters) but not passing orientation in (I think that PhotoScan doesn't use it even if you do provide?).

I'm looking right now to see if I can set up psuedo-gcps that can be used to correct elevation/rotation without altering the placement of the model in XY.