RoboRealm Forum

No Title

Tue, 30 Nov 1999 00:11:00 EST

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.

--patrick

No Title

Tue, 30 Nov 1999 00:11:00 EST

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.

Nemanya

Tracking a ball

Tue, 30 Nov 1999 00:11:00 EST

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!