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Author Topic: Capture distance vs reference Altitude  (Read 159 times)

andrevall

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Capture distance vs reference Altitude
« on: February 17, 2021, 07:34:16 PM »
I am in the process of building a 3D model of a city, using a set o aerial images. The images are acquired by an airplane, using a camera rig with 5 cameras: one looking down (nadir) and four looking obliquely (N,S,W and E) with a tilting angle of -45 degrees.
By reading the documentation, I found that in order to improve the speed of the camera alignment process, it is helpful to use the "Reference Preselection" setting, so that the algorithm knows which cameras are more likely to have matching points. Furthermore, it is recommended, in case of oblique images, to set the average altitude of the cameras in the "Capture distance" option of the reference settings.

My question is: is it necessary to set this "capture distance" option, in the case when the images altitude is already present in the reference panel? Is the images altitude already taken into account during the alignment process, or do I have to set the average altitude anyway? My fear is that the image-wise altitude is more precise than an average, so by overriding it with an average one I'm afraid to lose some accuracy.

Thank you

Andrea

Alexey Pasumansky

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Re: Capture distance vs reference Altitude
« Reply #1 on: February 17, 2021, 08:15:37 PM »
Hello Andrea,

If the cameras in the rig are synchronized (take photos simultaneously) and are rigidly fixed having their relative orientation fixed during the entire flight you can use multi-camera system approach when loading images to the chunk.

"capture distance" parameter will be only used, if camera orientation angles (yaw, pitch, roll) are also loaded to the Reference pane. If the distance between consecutive shots on the same flight line is short as well as a distance between the flight lines, I would suggest to use capture distance as an average height above ground value.
Best regards,
Alexey Pasumansky,
Agisoft LLC

andrevall

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Re: Capture distance vs reference Altitude
« Reply #2 on: February 23, 2021, 06:42:08 PM »
Hi Alexey,

thank you very much for the answer! Regarding the multi-camera approach: do you think that it would be possible to use it (with the GUI and/or with Python), even though I have some locations where some of the pictures are not available, like is shown in the attached image?

In case that is not possible, because the multi-camera system requires all the images in every location, what approach would you then suggest to use instead?

Thank you

Andrea