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Image collection height and lens type?

I am relatively new to aerial photogrammetry, but have been doing terestrial scanning for quiet some time now.  I have a couple questions that I seem to get varying answers on when searching.

First question, is there any benefit to flying a site at varying elevations for creating ortho photos?  For example, flying the site at 200 feet and then flying the same pattern at 400 feet?  Does this add any value or added accuracy?

Second question, is a flat lens better than a fisheye lens?  We are currently using a fisheye lense, but will be purchasing a new drone and camera and I wanted to know what your opinion was?

Thanks for your input

Chris,

 

From my own experience and research, I will try to answer both of your questions. In regard to your first question, I believe that flying at various heights provides greater accuracy as you can use the photos from further away to create the general layout of the site, and then use the photos that are closer to achieve greater detail. If I am correct, this should allow you to get away with slightly less overlap between photos at the 200’ mark in your example, as you can use the 400’ photos to build the larger picture.

 

To answer your second question, a flat lens is going to be the better option as you won’t get the distortion that you will with a fisheye lens. The primary use of a fisheye lens in photogrammetry is going to be when reconstructing interior spaces. Depending on your budget and the drone you intend to buy, your best bet would most likely be a camera with a manual zoom lens rather than your average point-and-shoot digital camera.

Great, thanks for your response.  As far as the different elevations, that was my thinking as well.

 

I would further second everything that Michael said. I did a project creating digital versions of 3D models of city- and landscapes from a nearby architecture school and acquiring images at different elevations above the model vastly improved the model. All was done with a flat lens as well.

Just be sure that your higher flight is nort more than two times the lowest. See the following link

https://support.pix4d.com/hc/en-us/articles/204656209#gsc.tab=0