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Follow a track

Make the simulated vessel sail a GPX track, a GPX route or a KML track. The track file reference lists what is read from each format and the simulation model explains how the vessel moves between the points.

From the desktop application

Choose File → Open track... (Ctrl+T) and pick the file. The current profile switches to track mode, the track appears in green on the map and the seek slider shows its length. Start sails it; Step and the slider move within it. The Mode group of File → Settings... holds the speed, the timestamp switch and the loop option, and File → Save profile keeps them. The tutorial walks through it.

From the command line

nmeasim run --track samples/saronic-gulf.gpx --tcp-server 10110
  • A timed track (every point has a <time>) is sailed on its own timing; speed and course follow from the timestamps unless the points carry <speed> and <course>.
  • An untimed track or a route is sailed at --speed knots (6 by default), or at the recorded point speeds when the file has them.
  • --ignore-timestamps sails a timed track at --speed instead.
  • --loop starts again at the first point; without it the run ends at the last point.

From a profile

Set the mode and the file in the simulation object, then run the profile as usual:

"simulation": {
  "mode": "track",
  "track": { "path": "saronic-gulf.gpx", "speed_kn": 7.5, "use_timestamps": true, "loop": false }
}

A relative path is resolved against the directory that holds the profile, so a profile and its track can be moved together. Everything the track does not carry, such as depth, wind and the GNSS quality, comes from the profile's seed; the variation values are not used while following a track. See the profile reference.

Checking what will be sailed

The track is loaded when the profile is applied, and a file that cannot be read or has no points stops the run with a message naming the point at fault. A quick way to check a file is to sail it to standard output for a few seconds:

nmeasim run --track my-track.gpx --stdout --quiet --duration 3 | head