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Author Topic: Convert UltraCamXp Calibration Report to PhotoScan Pro model?  (Read 2868 times)

JMerc

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Hello all,
I am attempting to use aerial photos (with high accuracy and precision camera locations) to extract surface elevation information without GCPs. There is about a 6 photo overlap between the photos in the area I am interested in (4-band imagery, including an infrared band). The ground resolution of the pixels is 30 cm. The camera used is a an UltraCamXp. A camera-specific calibration model has been created for the camera (see attached).

The problem is that I am at a loss as to how to convert the parameters within the provided documentation into something usable by PhotoScan. I've tried using what seem to be standard equations (e.g., some of the equations provided here - https://www.cs.umd.edu/class/fall2013/cmsc426/lectures/camera-calibration.pdf) to try and relate the given and desired parameters, but when I finally am able to run the model (after double and triple checking that the values make sense relative to each other), the output is garbage; it looks way better without the camera calibration. However, when I compare to validation points, the updated camera positions can be as much as 120 m off, elevation wise, and between 100-200 m off, horizontally. Once I re-run the model with GCPs, those values are off 10, and 15-25 m, respectively, though the whole point of my exercise is the not have to use GCPs.

I'm thus wondering if anyone has any ideas concerning a program or exact formulas one might use to perform an appropriate conversion related to fx, fy, cx, cy, k1, k2, and k3 given the documentation I've uploaded. I don't have access to the original camera, so I can't calibrate it using Lens.

Thank you for your time,

Jason

Paulo

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Re: Convert UltraCamXp Calibration Report to PhotoScan Pro model?
« Reply #1 on: June 04, 2015, 07:41:56 PM »
Hello,

the fx and fy values are in pixel and can be calulated as

fx=fy=ck/pixelsize = 100.5mm/0.018mm = 5 583.3333333333333333333333333333

cx=sensorwidth/2+XPPA/sensorsize = 5770/2 = 2 885

cy=sensorheigt/2-YPPA/sensorsize = 3770/2-0.12/0.018 = 1 878.3333333333333333333333333333

all ither parameters should be 0.

Supposing your images are from MULtispectral camera with 5770 by 3770 pixels and 0.018 mm pixelsize

Hope this can help
Best Regards,

Paul Pelletier

JMerc

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Re: Convert UltraCamXp Calibration Report to PhotoScan Pro model?
« Reply #2 on: June 09, 2015, 11:47:00 PM »
pap1956,
Thank you very much! This appears to have done the trick. Looks like I was trying to make things more complicated than they needed to be.

Cheers!