From: pierson@alcor.usc.edu (Harold Pierson) Subject: Re: TECH: Options for position sensors??? Date: 4 Apr 1992 10:45:48 -0800 Message-ID: Organization: University of Southern California, Los Angeles, CA In article <1992Apr3.054642.28942@u.washington.edu> James Gustave writes: >Can someone summarize the available options for position sensors? >I'm looking for something that would fit on a PowerGlove (to replace its old >ultrasound sensors), and I have to watch my budget. I don't mind going the >home-built route, but I'd need complete info. Anyone out there, please post them. I am looking for something I can build at home... >On a related note, has anyone successfully built their own magnetic position >sensors ala polhemus? How exactly do they work? Is there a lot of technology >in those li'l things? I considered looking up the patent info, but haven't >had a chance to yet. (If someone lives closer to a patent office, the number >is 4,737,794) I've looked up that patent plus one in the 3 mil range (Both are listed in the sci.virt FAQ under Polhemus) The design in the patent is NOT for a 6D tracker. It's for a 5D tracker. The three angle orientation of the object your tracking and the two angles, a la sperical coordinates, indicating the direction of the object from your origin. IT DOES NOT DO DISTANCE! In order to distance, you need two "origins" from which to track the object, then figure out its actual position via trig. The problem is, since it's a magnetic field, you can only use one of the two "origins" at a time. So you must swich between the first and second "origins" completely. And if you want to add another object, ie track two items at the same time, you need to switch between your all four of your object-origin combinations. Someone told me the IsoTrak (single object tracking) updated the position 60 times a second. For two objects, that number falls to 30 times a second. Three objects means 20 times a second, etc. Plus I can't imagine that calibrating the magnetic fields would be all that easy. At least for building one at home. Harry Pierson The Audio Mercinary pierson@usc.edu