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Using CHDK to mesure speed? Is it possible?

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Using CHDK to mesure speed? Is it possible?
« on: 12 / May / 2009, 18:55:54 »
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Is there a script that will measure speed or is there a way to use MD or any other script to measure speed?

Re: Using CHDK to mesure speed? Is it possible?
« Reply #1 on: 13 / May / 2009, 12:41:14 »
Hi Brandon,  the police use lines on the road.  Set the camera facing directly at the road  (perpendicular to car travel),  the measure the distance between two fixed points on the road,  or extent of camera view.  With an intervalometer script you can set  the time gap between shots.   Should be able to estimate speed by distance travelled/time between shots
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Re: Using CHDK to mesure speed? Is it possible?
« Reply #2 on: 13 / May / 2009, 14:12:39 »
Well, MD could be probably used for this if the object is noticeable enough (large enough & proper color compared to background) and doesn't move too fast (it'll probably have to take around a second or longer between appearing & disappearing from the screen to achieve satisfactory measurement accuracy).

In the MDFB script you can find an example for setting masks in MD, try e.g. 10 horizontal cells and set mask in a way that only cells on each sides are active for MD. Don't put any shooting related stuff in the script, instead just calculate time differences between triggers (10 ms resolution here, for accuracy calculations you will need to know that there is an additional longer and more or less random delay from MD reaction time (likely shorter than MD reaction time for shooting, though, commonly around 70 to 120 ms for camera models that have buffer optimizations in place for MD speedup)).

To calculate speeds from those times you will of course have to know how long the distance the object traveled, the camera can't really know that with ease (focus subject distance reading is inaccurate and only works for short distances).

 

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