[meteorite-list] GPS: Channels, post-processing, DGPS and AD at bottom

From: Thaddeus Besedin <endophasy_at_meteoritecentral.com>
Date: Wed, 11 Jul 2007 22:14:49 -0700 (PDT)
Message-ID: <500277.80225.qm_at_web62510.mail.re1.yahoo.com>

Note: I support the unregulated copying and
distribution of copyrighted materials, including
music, software, and scientific literature.
Garmin is the preponderant marketer and manufacturer
of commercial recreational/navigational GPS devices,
and so information regarding comparison to
under-represented alternatives that are equal to or
better than Garmin products is less commonly available
than biased pro-Garmin Internet presence.

Delorme Blue Logger GPS is a bluetooth-operated data
logger with a SiRF IIe/LP low-power 12-channel chipset
with WAAS DGPS capability (a single channel). It can
log raw SiRF protocol binary data, with L1 carrier
phase, C1 pseudorange, and D1 doppler encoding, which
can be converted using the included software into RAW
data, permitting differential post-processing against
data, available online, from DGPS stationary
continuous reference stations, once the RAW file is
converted into RINEX using proprietary DeLorme
software. 2.45-sigma accuracy is <1m, but, in open
places, accuracy of <0.75m is possible. DeLorme is a
little protective of its slight market share, so it
packages its GPS Postpro 2.0 software with an
Earthmate GPS receiver, which, if I am correct, must
be used as a hardware key with the Delorme software.
Warez are illusive and/or non-working. SiRF binary
protocol is modified in the Delorme version of the RAW
data file with proprietary sentences. An attempt to
translate these in Mac OS X is at Sourceforge
(http://bluelog.cvs.sourceforge.net/bluelog/). A
comparison demonstrating the excellent accuracy of the
Blue Logger against a Trimble Pathfinder Pro XR
sub-meter beacon-based DGPS unit is at
http://academic.sun.ac.za/forestry/precision/papers/39.pdf.

I would recommend, rather than Garmin, the Magellan
explorist-series 14 channel receivers(with dual WAAS
channel receiver dedication) I have used these since
2005, and in non-forrested preliminary archaeological
survey of land, are nearly always accurate to <2m
(with sufficient satellite signal/channel activity).
These are available for very low prices, and are
certainly more accurate than the non-post-processed
Garmin receivers of the same class (like the etrex
series). Magellan receivers of this series cannot be
post-processed.
Garmin, if its binary data stream is logged, can be
converted to RINEX for
post-processing. I am not sure of the post-processed
accuracy. Garmin data can be converted to RINEX using
GRINGO software (http://www.helenav.nl/,
http://gpsinformation.net/pseudorange.htm,
http://www.ultimategps.com/garmin_gps_software.html).

By the way, I have a Magellan eXplorist 200
(14-channel WAAS, <3m) receiver for sale, in excellent
working and good cosmetic condition (some abrasions
and minor scratches). I want $40.
-Thaddeus






       
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Received on Thu 12 Jul 2007 01:14:49 AM PDT