Hi Most fire towers have a pretty good view of the surroundings. How about simply picking an adequately remote point and using that (based on map data) as your direction reference? If you get lucky the fire tower is actually a survey tower that got converted to fire use and there's a very well known location for the tower.
Bob -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Attila Kinali Sent: Thursday, August 26, 2010 11:20 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Slightly OT - GPS-Based Accurate Direction Finding On Fri, 27 Aug 2010 00:09:31 +1000 David Smith <[email protected]> wrote: > Some background - I'm needing an accuracy of 1 degree or better. The > experiments are using digital communication modes and sometimes aircraft > scatter so signals are regularly inaudible and often non-existent, so > peaking "by ear" is not usually an option. 1 Degree isnt that hard. Even a standard magnetic compas reaches that. I've quite an old one at home with prismas for aiming with which it is possible to get better readings than 0.5°. Of course, you'd have to take the deviations from true north into account. But magnetic maps should be readily available (at least they were when i was a scout). > As Atilla says, the software is probably not that fundamentally > complicated. However, the devil is possibly in the detail of aligning > sample timing, positioning ... You don't have to allign sample timing. It is helpfull though, to get better precision/accuracy. It is enough that you use the relative phase differences of the SV on each GPS module. This way you can get rid of the unknown sample phase difference of the GPS modules. (the principle is the same like normal GPS measurement using a 4th satelite to get rid of the unknown "time"). I just had a look at the LEA6-T protocol specs. The RXM-RAW message provides you with a phase difference (in L1 cycles) and a frequency offset (doppler, in Hz) and pseudorange (in meter) for each SV that is being tracked. With this you should be able to eliminate the phase and frequency difference/drift between the two modules. Using a long enough measurement time, you should be able to get to well below a degree of heading accuracy. I know that the ETH in Zürich uses LEA6-T modules to get positioning resolutions better than 2mm with single GPS modules, though they have to collect more than an hour of phase data for this. Attila Kinali -- If you want to walk fast, walk alone. If you want to walk far, walk together. -- African proverb _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
