Thanks for checking out phpBathymetry
This software is truly a casserole of confusion at the moment, stemming from developing software while floating along in a boat, fishing for trout.
Trout fishing has some quiet time for reflection, and it made me consider all the wasted data my Lowrance Elite 5-DSI was generating. Latitude, Longitude, Altitude, depth, top water temperature and I had some time to kill...
The result is 2 scripts.
One is the nmea.php
Designed to use a COM port from Windows (swappable to /dev/ttyS?_) and manage a buffer and NMEA message parsing, nema.php digests verbose NMEA messages down to timestamped, comma delimited data files.
log-analysis.php
this script globs the current directory for all the files that were created by nmea.php. It replays the files sample by sample, converting Lat/long to relative pixel positions on a GD canvas. Depth is indicated by color, configurable, but currently sweeping from light green over shallow to dark blue over deep. It coughs out a number of PNG files, depth, water temperature and sample frequency.