Tracking a ball
Ken from United States  [2 posts]
15 year
Is it practical to use Roborealm to track a thrown ball while its in the air? Are there camera and/or framerate issues I should consider? Great program BTW. Thanks!
from Australia  [87 posts] 15 year
There will definitelly be frame rate issues, but anything is possible in a controlled environment.

First, try and get the fastest camera you can... firewire can cope. U need short exposure times to prevent blurring...

Now the question is whether it is indoors or outdoors? The idea is to flash a light source fast enought, as this acts like a super fast camera shutter. That way you can get multiple images of the ball in the same frame that are spacially separated due brief flashing time intervals.

How's that for a start? You can always reverse the concept and make the ball flash very quickly and use an average cheap camera.

from United States  [214 posts] 15 year
The biggest issue I have encountered when trying to track a fast moving object is keeping it in the field of view (FOV) of the camera.  In other words, if you are using a typical webcam with about 45-60 degrees FOV, a quickly moving object can get from one side of the field to the other within a single frame transition.  So depending on the conditions under which you want to track the ball, I would think you need to look at both frame rate and the size of the FOV.  I have a Creative Labs Live! Cam Voice which has one of the larger FOVs among webcams at 85 degrees.  On the other hand, the fastest frame rate I have found on a webcam is the Philips 1300NC at 60-90fps.  (In the real world I get about 50-60fps with RoboRealm).

Having said all that, a thrown ball has a fairly predictable trajectory from the physics (assuming no wind) so you should have an easier time tracking it using some prediction in your camera motion.  I use a similar technique to have my robot "catch" a rolling ball--by estimating the approaching speed of the ball from successive sonar measurements, then computing an ETA so the arms can begin closing before the ball actually arrives.


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