From ascen@world.std.com Tue Sep 20 12:41:16 1994 Return-Path: Received: from mx1.u.washington.edu by stein2.u.washington.edu (5.65+UW94.4/UW-NDC Revision: 2.30 ) id AA27724; Tue, 20 Sep 94 12:41:16 -0700 Received: from hitl-new.hitl.washington.edu by mx1.u.washington.edu (5.65+UW94.4/UW-NDC Revision: 2.30 ) id AA10947; Tue, 20 Sep 94 12:41:15 -0700 Received: by hitl.hitl.washington.edu; id AA21724; Tue, 20 Sep 1994 12:39:45 -0700 Received: from relay3.UU.NET by rodan.UU.NET with SMTP id QQxife12715; Tue, 20 Sep 1994 15:41:12 -0400 Received: from uucp3.UU.NET by relay3.UU.NET with SMTP id QQxife23983; Tue, 20 Sep 1994 15:41:11 -0400 Received: from world.UUCP by uucp3.UU.NET with UUCP/RMAIL ; Tue, 20 Sep 1994 15:41:17 -0400 Received: by world.std.com (5.65c/Spike-2.0) id AA19130; Tue, 20 Sep 1994 15:35:26 -0400 Newsgroups: sci.virtual-worlds Path: ascen From: ascen@world.std.com (Ascension Technology) Subject: Re: TECH: tracking in metallic environment Message-Id: Organization: The World Public Access UNIX, Brookline, MA X-Newsreader: TIN [version 1.2 PL2] References: <35a7hm$i5n@news.u.washington.edu> Date: Tue, 20 Sep 1994 19:35:21 GMT Lines: 70 Apparently-To: uunet!sci-virtual-worlds@uunet.uu.net X-Status: Status: OR Fred Sistler (fsistler@ocular.bae.lsu.edu) wrote: : -- : Does anyone have suggestions on how to do 3D tracking in a metallic : environment? We have Flock of Birds which works in a non-metallic : environment, but our application is right in the middle of all kinds : of metal - i.e., a processing plant. I talked with Fred Sistler's grad student (Roy Vanholden) and his working environment is very hostile to magnetic based trackers of any type. The system is loaded with moving ferrous-metallic objects. The Ascension Tracking system uses DC Pulsed magnetic fields which drastically reduces or eliminates eddy-current generated distortion. (Any conductive material will generate eddy-currents when exposed to changing magnetic fields, which in turn generate magnetic fields that can distort some magnetic based trackers.) Because Ascension's Flock of Birds uses pulsed DC, we can measure the field after these distortions drop-off (later in time). [See our technical paper on FTP site: FTP.STD.COM under /ftp/vendors/Ascension] The other potential problem is ferrous-magnetic properties in some metal that can distort any magnetic field lines. This is not usually a problem, and there are steps that can be taken to reduce this effect, including: 1. Repositioning/reorientation of transmitter with respect to receiver. (if possible, keep distance from transmitter to receiver less then distance of transmitter to large amounts of ferrous metal.) 2. Mapping magnetic fields distortions. (We do this occasionally for people who want better then advertised position/orientation measurement, but can also be used to correct for ferrous-metallic interference.) Unfortunately, the environment (a processing plant) is full of moving ferrous-metallic structures, all impractical to mapping, and from talking with Roy Vanholden; repositioning transmitter is not practical. Fred Sistler's lab has successfully used the Ascension Flock of Birds tracking system for a number of studies. It seems from talking with Roy Vonholden that in this one situation, they are in too harsh an environment for our tracker. Regards, Steve Work Ascension Technology Corporation Technical Support : -- : o o o o o o o . . . _________________________________ _____=======__T__ : o _____ |Fred Sistler | | | : .][__n_n_|DD[ ====|____ |Bio & Ag Engineering Dept. | |(504) 388-1057 | : >(________|__|_[___/_____]_|Louisiana State University____|_|_FAX: 388-3492 |_ : _/oo OOOOOO o` ooo ooo 'o^o^o o^o^o` 'o^o o^o` : -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-