>>>>> "Daniel" == Daniel Johnson <[EMAIL PROTECTED]> writes:
Russell> I bought a BU-353 recently. Plug it in, it starts sending Russell> NMEA sentences at 4800 baud. Gpsd was talking to the device, Russell> and I used "gpspipe -r" to cat the data into a file. I've Russell> got complete second-by-second track information for a trip to Russell> the bay area i took a couple months ago. I haven't gotten Russell> around to figuring out how to draw it nicely on a map, but Russell> the data is there. Daniel> With a laptop I could record the NMEA, but I don't exactly Daniel> want to carry a laptop to map a hiking trail which is the Daniel> problem. I was using a wireless access point, a Netgear WGT634U, which has a USB host port, runs linux, is thus quite hackable. Storing data onto a usb keyfob. Smaller than a laptop, but still larger than ideal. A $100+ li-ion (Polarmate PM85-44) battery could power that rig for ~6 hours. Daniel> Now I had the idea that if I had two gps's both making Daniel> tracklogs, one hidden in my car, and the other with me on the Daniel> trail, that I could use the fact that one is standing still to Daniel> correct randomness of the one that travels with me. You can't. Consumer grade GPS's don't export the information that would make that possible. You need differential GPS, where the static location is constantly updating the mobile one re per-satellite jitter over a radio. All the GPS stores/reports is the final fix, not the per-satellite arrival times, which is what you need to correct your fix calculations. Daniel> It is really frustrating to walk a loop trail, and not have Daniel> the end match the beginning because the accuracy drifted from Daniel> one visit to the next. A normal GPS ought to get you close enough, like 15 feet or so. What might be screwing you up on hiking trips is multipath. The signal from the satellite is bouncing off of adjacent slopes and confusing the signal. The bounce path is longer, so your fix ends up considerably off. You see this a lot in downtown environments with tall buildings. Daniel> I seemed to remember that was only one of the options when I Daniel> played with it at the store, and pure time hops was another Daniel> option. Oh. That's possible. Maybe a newer model or just a feature I don't use. My Garmin 12CX only holds 2048 track points. In that context, I like the redundant point dropping mode. -- Russell Senior ``I have nine fingers; you have ten.'' [EMAIL PROTECTED] _______________________________________________ PDXLUG (a Portland Linux user group) mailing list [email protected] http://lists.pdxlug.org/mailman/listinfo/pdxlug IRC: irc.freenode.net #pdxlug & #orlug
