On Sat, 2007-03-17 at 19:58 -0400, Doug McGarrett wrote: > On Saturday 17 March 2007 13:13, Roger Oberholtzer wrote: > > On Fri, 2007-03-16 at 19:15 -0400, Doug McGarrett wrote: > > > The GPS downloads the Zulu time with every transmission. > > > The only delay would be decoding the actual transmission. > > > and it went on from there, in the list. I think a lot of us would like > to know, if it is within the clearances of your company, why you are > trying to pinpoint the location of a vehicle moving at 60 MPH or so > (100KPH) to within 1 meter. Such a vehicle would probably be moving > slower than the old German Buzz-bomb, but faster than a taxicab, and > who cares what the exact position of a cab is, so why would you want > to know to that accuracy?
We measure road surface conditions. Things engineers want to know in order to track road wear. So they can evaluate construction methods, materials, and plan maintenance in an objective way. These engineers (world wide) have been reading the big print in GPS and INS advertisements and are asking for locations these adverts claim to be possible. They never read the fine print that tells the conditions under which these levels of accuracy are possible. A GPS receiver can provide data at 10 Hz. At 90 km/h, that is one value every 2.5 meters. So, we need to report accuracies at almost 1/3 the measurement rate. Ain't gonna happen. So, one needs to add inclinometers, gyroscopes and other doodads to fill in the spaces. This require time synchronization between the GPS and the other transducers. Not to mention that GPS has drift, multipath error and other little nasties. What they dream of is that a vehicle will roam the highways and when the data is returned, it will magically be identified. To compare subsequent measurements requires some level of accuracy in locating the data. There are existing identification systems, but these are difficult/expensive to maintain, compared to a GPS method. There are some basic flaws in this collection methodology, but it is even more beyond the scope of this group. Wow, even more off topic... -- Roger Oberholtzer OPQ Systems / Ramböll RST Ramböll Sverige AB Kapellgränd 7 P.O. Box 4205 SE-102 65 Stockholm, Sweden Tel: Int +46 8-615 60 20 Fax: Int +46 8-31 42 23 -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
