Marker Size - help

[ReginaK]

I'm using a Canon SX260 on a UAV, when flying at 950 feet, whats the size of the markers I have to make? Is 50x50cm good? Please someone help me on this...

Thanks

[RalfH]

At what focal length?

Generally, you can calculate your angle of view (http://en.wikipedia.org/wiki/Angle_of_view) from sensor size and focal length. From this, you can calculate the angular pixel resolution. Using this and the distance between camera and the ground surface, you can calculate how many pixels are equivalent to an object of a certain size on the ground surface.

P.S: I have been using 20 cm tagets for PAP (6 metre pole) with 28-50 mm focal length (35 mm equivalent). That's quite big, but remember that you will also have to find your targets in the photographs (unless you use automatic recognition), so they shouldn't be too small.

P.S.2: If your camera is set to wide angle (25 mm at 35 mm equivalent), the angle of view (sideways) is 71.5°. At 4000 pixels image size, this means that one pixel has a size of 0.0179°. At a distance of 950 feet, one pixel is equivalent to 0.3 feet. Your 50 cm targets would have a diamteter of less than 6 pixels - that's very small.