Skip to content

Following a GPX track

In this tutorial you make the simulated vessel sail a track recorded on a real trip, watch it on the map, jump around in it and hand the stream to a chart plotter. It takes about ten minutes. You need the desktop application and a GPX file; the repository ships one under samples/saronic-gulf.gpx, a passage from Piraeus past Aegina to Agistri.

1. Open the track

Start NMEA Simulator X and choose File → Open track... (Ctrl+T). Pick saronic-gulf.gpx. The current profile switches to track mode: the status bar reads Stopped - Default (track saronic-gulf.gpx), the map shows the track as a green line with a marker on every point, and the vessel sits on its first point off Piraeus. The seek slider in the toolbar becomes active and the label next to it shows 00:00 / 3:01:36, the length of the track from its timestamps.

Notice that the override boxes on the dashboard are greyed out: while a file drives the vessel, the position, course and speed come from the file.

2. Sail it

Press Start (F5). The vessel leaves the harbour at the pace the track was recorded, about seven knots, and the red sailed track grows over the green one. The Time (UTC) tile shows the time recorded in the file rather than the wall clock, because the track has timestamps. Type RMC in the console filter to see position, speed and course change with every sentence.

3. Jump ahead

Drag the seek slider to about two thirds of the way. The vessel jumps to that point of the track at once, the label shows the new elapsed time and the stream continues from there. Press Step (F7): the run pauses and each further press advances the simulation by one tick. Untick Pause (F6) to continue.

4. Sail it your way

Open File → Settings.... In the Mode group the track is already selected. Untick Follow the track's own timestamps and set Speed without timestamps to 20 knots, then press OK: the same track is now sailed at twenty knots and the clock follows the wall clock. Tick Start again at the end to let it loop.

A route file has no timestamps at all: open samples/saronic-route.gpx to see the vessel sail from waypoint to waypoint at the configured speed.

5. Connect a plotter

The TCP server on port 10110 is still part of the profile, so a chart plotter connected as in Your first simulated voyage sees the vessel follow the track. This is a convenient way to replay a real trip through software under test, with the timing, positions and courses of the original.

6. Keep it

File → Save profile as... stores the mode, the file and the options with the profile, so nmeasim run --profile passage.json sails the same track headless. The file path is saved as given; keep the track next to the profile and use a relative path in the file to move them together.

Where next