<< return to Pixycam.com

Measurement / Tele lens

Pixy Hardware
#1

Hi all

Can I use the Pixy to measure the distance to the tracked object (e.g. colour coded object)?
This if for an art project of mine where I need to know the distance between 2 poles carried by performers.
The distance can range between 0,5 and 10 meters (max!). It could possibly be assisted by an ultrasound sensor.

Another related question is: do I need a tele lens to view the other pole at 10 meters distance. Is there a lens I can use?
For another project (The iSemaphore Project (http://philippedruez.be/isemaphore) I used a Canon 70-200mm tele-zoom that I used with a hacked Logitech Ultra Vision webcam. This worked great (like a 1500mm tele!).

Philippe

#2

Hi Philippe! Nice to hear from the art side of things. You could write some code to get a rough estimate of distance using Pixy - it does report the size of the objects it’s detecting, so you could conceivably use changes in relative size to estimate distance.

Re: the tele lens, that depends on the size of the object you’re tracking. I can’t tell how big the pole is from the picture you attached, but rule of thumb is that Pixy can detect a table tennis ball at 3 meters with the normal lens. If you need, you can get a compatible zoom lens here: http://www.mindsensors.com/ev3-and-nxt/50-tele-lens-for-nxtcam-pixy

Let me know if you have other questions!

Cheers,
Jesse

#3

Hi Jesse

Thanks for the information and link! The pole (called macePod) will be some half meter above the person carrying it (possibly in a crowd). It has a circumference of 40cm at least but the shape is different from different angles of view (see image). If I can use the Pixy to track the object (with a pan-tilt) then maybe I can use an ultrasound for the distance. Accuracy should be 5cm at least. Or is a firmware update a possibility. I guess other users can use a z-parameter (distance measuring) as well.

Best,
Philippe

#4

Hi Philippe,

it’s unlikely that we will have a firmware update addressing that any time soon. I’m not the software guy, but I think adding distance calculation is pretty tricky when there are so many potential objects that Pixy can track (hundreds at a time) and they don’t keep unique IDs. That said, I’ll add it to our feature request list.

It sounds like you will probably need a tele lens to make the colored bits of the pole detectable by Pixy at distance. Let us know how it goes if you decide to try it!

Best,
Jesse