Uploading Large Files to the Garmin inReach Explorer+

I was joining my friends for a section of their Catamount Trail thru-ski down Vermont from Canada to Massachussetts. They brought a Garmin inReach Explorer+ and wanted a map of the trail on device for redundancy. The Garmin website explains how to do this:

  1. Upload GPX (or KML or KMZ) file to your account on the Garmin Explore website
  2. Install inReach Sync desktop app and login with your Garmin account
  3. Connect inReach to computer via USB and use inReach Sync to sync the uploaded file from account to device

I downloaded the GPX files from the Catamount Trail website and found I could upload to Garmin as "tracks" or "routes". When I tried uploading as route, I found the upload to be much more coarse than the original GPX file (far fewer waypoints). But uploading as a "track" wasn't even usable for navigating. The Garmin website said about routes: "Any line will be reduced to 200 data points." I couldn't find anything else from Garmin about specific file constraints so I started experimenting to get the map on the device in full resolution.

GPX Background

GPX is just an XML schema. It can represent things like a "route", which is a series of points to be followed, and a "track", which is a series of points (optionally timestamped) representing a journey taken: 

<?xml version="1.0" encoding="UTF-8"?>
<gpx version="1.0" creator="GPSBabel - https://www.gpsbabel.org" xmlns="http://www.topografix.com/GPX/1/0">
  <time>2022-01-13T18:37:13.323Z</time>
  <bounds minlat="42.739060000" minlon="-72.945140000" maxlat="42.801320000" maxlon="-72.910070000"/>
  <trk>
    <trkseg>
      <trkpt lat="42.739060000" lon="-72.925210000"/>
      <trkpt lat="42.740510000" lon="-72.923980000"/>
      <trkpt lat="42.740640000" lon="-72.923910000"/>
      <trkpt lat="42.740640000" lon="-72.923910000"/>
      <trkpt lat="42.740920000" lon="-72.923760000"/>
    </trkseg>
  </trk>
</gpx>

The GPX file from the trail association had a single track, with a single track segment, with about 17,000 points over ~300 miles (one waypoint every ~100 feet). Even though the file contained a track, it could still be uploaded as a route to Garmin.

Splitting the GPX file

I looked for a tool to split a GPX file into smaller parts. I found lots of software that I couldn't get to work:

But then a post on the GIS stackexchange explained how to do it with gpsbabel: 

#!/bin/bash

# $1 shall be the gpx file to split
pfx="${1%.*}-"
gpsbabel -i gpx -f "$1" -t -o csv -F - \
| gsplit -d -l 200 --additional-suffix=.csv - "$pfx"

for f in "$pfx"*.csv; do
    fout=${f%.*}.gpx
    gpsbabel -i csv -f "$f" -x transform,trk=wpt -x nuketypes,waypoints \
                        -o gpx -F "$fout"
    rm "$f"
done

It converts the GPX to a CSV, chunks the CSV into smaller CSVs, then converts each CSV back to GPX.

So now instead of one GPX with 17,000 points in a single track segment, I had 86 GPXs, each with a single track of 200 points. They could be losslessly uploaded to Garmin as routes, but I would have to upload them by hand.

Concatenating the smaller files

I've been doing a lot of functional programming lately, so I used a "fold" to accumulate the output GPXs into a single file (yikes): 

#!/bin/bash

# $1 is input
# $2 is output
# $3 is (optionally) max number of points per file

prefix="${1%.*}-"
gpsbabel -i gpx -f "$1" -t -o csv -F - \
  | gsplit -d -l ${3:-200} --additional-suffix=.csv - "$prefix"

echo -e "<?xml version=\"1.0\" ?>\n<gpx>\n</gpx>" > "$2"
for f in "$prefix"*.csv; do
    gpsbabel -i csv -f "$f"                              \
             -i gpx -f "$2"                              \
             -x transform,trk=wpt -x nuketypes,waypoints \
             -o gpx -F "$2"
    rm "$f"
done

There is definitely a better way but this one worked. A single GPX with 86 tracks, each with a single segment of 200 points. It may be that 1 track of 86 segments would work too.

hi