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[gpsd-users] SDDBT

From: bertram waterman
Subject: [gpsd-users] SDDBT
Date: Sun, 8 Jan 2012 16:37:12 +0000

As a new member to your mailing list I apologise in advance for a) silly questions and b) very rusty C skills ( I programmed mainly in Fortran and that was a long time ago!)

OK, Two or three hopefully straightforward questions and some background

1. I'm tinkering with a small project to hopefully run on on a Rasperry-PI involving basic sea-floor mapping using simple consumer grade electronics all of which output NMEA sentences. The current setup uses a gps receiver that outputs serial NMEA. this in turn is fed into an echo sounder unit which re-transmits GLL etc. ( I know there will be some latency but I can live with this),  together with the $SDDBT sentence (depth below transducer).  Now for sea-floor mapping, I clearly need the x,y,z,triple but as it stands, I believe that gpsd will ignore the SDDBT sentence but simple pass it through in nmea mode. Trawling through your mailing lists I see the subject of including DBT was discussed in the latter part of last year but in the absence of any further info, can I assume that any proposed support has been dropped? ( I suspect OpenCPN would use it if available). If so, then I suspect it will be easier for me to just use gpsd as a NMEA "socket" and parse the sentences myself. Using usblib would not really an alternative as I can envisage multiple clients.

2. I've been writing a small C routine to act as a client in preparation for having to parse the NMEA but as yet can't seem to find the correct combination of flags to suppress the JSON report - even with WATCH_ENABLE|WATCH_NMEA I still seem to be getting the JSON report where I only want to have to parse NMEA. Is the output affected by the input? i.e I'm currently using a little Sirf based gps puck for code testing at home which outputs binary, on the boat it will be pure serial.

3. Finally, looking through the sources (driver_nmea.c) I see that the OHPR sentence/device is supported and depth is added to the attitude structure. Now my C skills are just about up to cobbling together a NMEA parser - is there any scope there for a user hack? (obviously using a different structure).

Jonnie H

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