Raw Data in Garmin Etrex
Antonio Tabernero Galan
It was pointed out that the Garmin Etrex doesnt output raw data
information in the same format as the G12 family. However, after
a brief examination of a binary log kindly supplied by DJ Johnson
it seems that very similar info is present in the async messages
sent by the Etrex.
It only happens that Garmin thought to improve on its undocumented
messages by shuffling the fields within most messages. Here comes a
brief description of where the interesting info is to be found in
the Etrex. There is no description of the fields as they are common
with the already described ones for the G12 family (for those not
familiar with those have a look at
http://artico.lma.fi.upm.es/numerico/miembros/antonio/async/
Since the interesting info seems to be there all right it would also be
possible to generate a Rinex file from a log of the Etrex. In order
to do so the latest version of gar2rnx has an -etrex option.
I havent done any testing whatsoever of the resulting RINEX files
since I dont have access to an Etrex. Let me know if this is working
for you.
Antonio.
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---------------------------------------------
RECORD 0x1a (L=12 x 8 bytes)
---------------------------------------------
Same as in the G12 family. Twelve eight-byte records, one for each
channel.
The fields are exactly the same though most are in different positions:
Bytes 1-2: Fractional Phase
Bytes 3-4: signal_Q
Bytes 5 : elev
Bytes 6 : svid
Bytes 7-8: tracking status
--------------------------------------------
RECORD 0x36 (L=12 bytes)
--------------------------------------------
Bytes 1-4 : c_50
Bytes 5-8 : unknown
Byte 9 : svid
Bytes 10-12: three aditional new bytes. In my (very) short piece of
evidence
they are fixed for all sats.
--------------------------------------------
RECORD 0x38 (L=40 bytes)
-------------------------------------------
Same info as in the G12 messages with three additional bytes added at
the
end. The position of the old fields is as follows:
Bytes 1 - 8 : Pseudorange
Bytes 9 -16 : Tow
Bytes 17-20 : Phse_counter
Bytes 21-24 : tracked
Bytes 25-28 : Integer Integrated phase
Bytes 29-32 : c_511500
Bytes 33-34 : delta_f
Bytes 35-36 : signal_Q
Bytes 37 : svid
Bytes 38-40 : new bytes.
--------------------------------------------
RECORD 0x16 (L=24 bytes)
--------------------------------------------
Bytes 1 - 8 : Pseudorange
Bytes 9 -12 : Delta Pseudorange
Bytes 13-16 : f1
Bytes 17-20 : f2
Bytes 21 : svid
Bytes 22-24 : new bytes