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Unread 12-01-2012, 19:18
Greg McKaskle Greg McKaskle is offline
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Re: pixel granularity with axis camera

That is correct, the white paper has an error in calculating the example distance, but the formulas are correct. Using the correct value of 5.7 gives a distance of 13.1 ft. As mentioned in the paper, the actual lens view angle is a bit different from the data sheet. That calibration was not based on the example data. The example coded in LV is not surprisingly correct when dividing by two, and gives the correct distance value.

The calculations in the camera size section are not impacted by the previous error. To elaborate a bit, the point where a 2" element is 2 pixels wide is where the field of view is 320 pixels and 320" wide. Half of 320 is 160" or 13.3 ft. 13.3 / tan( 47 / 2 ) is a bit over 30 ft.

Using the equations from the paper, it predicts that at 95" from the target, the target will be 93 pixels wide. At 96", it will appear 92 pixels. So it would appear that we are in mathematical agreement.

This observation calculates the expected error term of the distance at around 8 ft, or 95 in, from the target is plus/minus 0.5 inches. I don't really believe that is a problem. At 27 ft, it looks like error term is plus/minus 6 inches. I'm not going to claim that is ideal, but I would expect the variability of the balls and other mechanical shooter elements will likely be similar.

I hope that helps explain things a bit.

Greg Mckaskle
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