Difficulties getting orthomosaic with long focal length

[gimp3695]

I'm having difficulty getting good alignment with a 200 mm prime lens on a Canon SL1 flying in an aircraft at 6000 feet above ground level.

Previously I had flown a 55 mm lens on a Canon Rebel T3i at a lower altitude of approximately 2500 feet AGL and the images (without any GPS exiv) data worked almost flawlessly. The alignment looked great, dense cloud was good, it just all worked.

With this new camera and flying higher trying to do aerial photography the data is all over the place. Below are some screenshots of what I am referring too.

First is the original Rebel T3i (55mm @ 2500')

Next is the bad Canon SL1 (200mm @ 6000')

I've also attache the report output.


Things I have tried.

1. I tried with and without the GPS reference positions
2. I've tried creating 10+ GCPs and more tie points that I care to do.
3. I've looked at the image quality and its anywhere between 0.6 to 0.93
4. I've tried calibrating the camera using the Agisoft Lens software and using those parameters

My question is this. Has anybody had success at such long distances with long focal length lens doing orthomosaics? What am I missing?

The report shows the DEM varies between -6 KM and +9 KM.
The error on camera positions is -400 to 400 meters!! I can see +/- 50 meters but not that high.

Thank you in advance!

[Paulo]

I am wondering if your photos altitud or Z is correct?

Is it around 6000? than maybe your Exif data has registered Z in feet instead of meters?

You can always try genereic preselection without reference data ...

[gimp3695]

Thank you Paul,

I'm pretty sure it is correct. I set the average altitude for the reference settings in Meters and I made sure the EXIF was in meters and the difference between the two is correct.

Also yes I have tried with zero reference values from the photos and it is still just crazy bad.

[gimp3695]

Now that Christmas break is over. Just bumping this. Has anybody used Agisoft with 200 mm focal lengths at high altitudes?

[frank.stremke]

hi
i have not tired it from this height but i had sucess with images taken from an airliner in cruise just for fun...
however i think the problem is not the height but instead its the focal leghth
while big is good for nice orthos and traditional photogrammetry it is very bad for agisoft
agisoft does not like it it preferes light wide angles the largest i have ever used was 80mm that worked ok but given the nature of the geometry i can imagine 200mm will not realy work.
if its the same area i would recomend alligning the two sets together and see what happens then you can disable the 55mm ones
frank

[gimp3695]

Frank,

Thank you for your response. It is kind of what I figured. A lot of commercial software has not been created for long focal length lenses. I'm working with Alexey through support and I'm getting him more sample sets to see what he can come up with.

[ruyi7952]

Hi

A long focal mirror means a smaller field Angle, a larger distortion.
Normally I would suggest an equivalent 50mm lens or a 35mm full-frame lens.


Let's say you have the right overlap,

Try using no distorted pictures.

I hope I can help you.