Aerial images for ortho-mosaics, camera settings and more

I'm about to make a first try of an ortho-mosaic aerial image of an area about 600m x 600m.

I plan a forward overlap of about 80% and a sidelap of about 60%.
Does that sound reasonable?

Which shutter speed is appropriate for AGL=150m, v=10m/s, f=20mm?

The area I'm about to map is not totally level, AMSL is between 500m and 580m.
For optimal post-processing, shall I aim at constant AGL or constant AMSL?

I also appreciate any other beginner's hint(-s).

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Replies

  • Thanks a lot for the valuable input.

  • Constant AMSL (waypoints will be set this way by default)

    Anything above 1/1250 is very safe, take a picture on the ground to make sure it's not requiring a very high ISO though. If you get ISO 100 at 1/1250 then you'll be in good shape.

  • Reto,

    I'm not want to discourage you about doing AP (aerial photography), but many other parameters must be taken into account; after all you got to synchronize two systems: plane-APM and a camera and each one has many variables. Since you are going to take a picture, distance from camera to object is crucial (meaning here UAV altitude). Ideally you should keep same altitude AMSL through the trip so as to keep the images representing the same magnification level under the same resolution set; otherwise closer objets (mountains) will look smaller than they are and edges of the pictures will not match each other during processing. If you are going to do this by trial-error till you get an acceptable result is fine to test several setting at several flights, but I do not recommend you such way because the possible combinations of parameters is huge!. You can google some basic AP calculators for this; some of them are based on specific commercial camera models like Sony NX5, other calculators are more generic but more inaccurate. Concerning your overlaping, a forward 60% linelap and 20-25% sidelap is fine. Keep in mind what seems obvious in regular photography: the farther (elevated) the camera, the bigger the landscape captured but the lower the resolution obtained; the faster (speedy) it goes, the more frequent the shooting pace must be to keep overlapping among pictures. Likewise, as more elevated it goes, the faster it must move because it capture more lanscape every shot (supposing shooting pace remains the same). Untill here the relaxed way. But if you really want to understand and predict your settings and hence results with some accuracy before burning tons of batttery mah, I recommened you for starters to read some about photography (focal distances, field of view -FOV-, camera film, CMOS and CCD sensors, understanding pixel resolution and true pixels), then identify what type of sensor and resolution your camera does boast as to understand a bit better the tool you get. Then jump back to some googled AP calculators and you will understand better what parameters are asking for, or if you are more geek or math leaned, tailor by yourself in excel or mathlab your own calculator as I did my current one. Last hint: before expending those bugs burning your pocket in specialized software either on-line or installed, make a couple of rehersals with your pictures by using a google earth print-screen image of your target site as guiding background and overlaping 15-25 stills by photoshop or any cheap image editor allowing layers: in one hour you will see whether last settings worked out or not before swimming with GPS tagged images processing.

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