GTM — GPS Track Maker: Brazilian veteran format for 1990s GPS devices
GTM (GPS Track Maker) is a binary file format for storing tracks, waypoints, and routes, developed by Brazilian geologist Odilon Ferreira Junior in 1996. The eponymous GPS Track Maker application was for a long time the most popular GPS manager in Brazil and Latin America, especially for geologists, biologists, and hikers with legacy Garmin GPS 12/GPS 60 and Magellan Meridian receivers. The format never gained international traction, was edged out by GPX, but in Brazil and among vintage-GPS collectors .gtm lives on. If you pull an old Magellan eXplorist 200 from its box and want to load a route — chances are GTM is the only path.
History: from Belo Horizonte 1996 to forever freeware
Odilon Ferreira Junior is a Brazilian geologist from Belo Horizonte, Minas Gerais state. In 1996 he ran into a mundane problem: his Garmin GPS 38 receiver could save tracks internally but had no good way to export data to a computer for later analysis. Tools that existed back then were either paid, required Windows 95 + specific COM cable, or simply didn't work with Garmin GPS 38.
Odilon wrote his own program — GPS Track Maker for Windows 3.1. It read receiver data over RS-232, saved in a proprietary binary format (.gtm), allowed track editing, map visualization, export to simple coordinate tables. The program was free (freeware) and spread quickly through Brazil's nascent internet.
By 2000 GPS Track Maker supported over 200 GPS receiver models from Garmin, Magellan, Trimble. The .gtm format became the standard for Brazil's GPS community: geologists at Vale, biologists at WWF Brazil, hikers in Mato Grosso province — everyone used it for track exchange.
After 2005 the arrival of GPX (OpenStreetMap and Garmin standard, open XML) began crowding out GTM. But Odilon continued to support the program. GPS Track Maker 13.9 (2017) was the last major release. Today (2026) development is effectively frozen, but the program can still be downloaded for free from gpstm.com, and the .gtm format is read by several modern tools.
What's inside a GTM file
GTM is a binary format with a fixed header and variable body. Unlike GPX/KML (XML text) you cannot open it in a text editor and see structure.
Header contains: - Magic number (format identifier) - Version - Counts of waypoints, tracks, routes - Bounding box (min/max coordinates of all data) - Coordinate system (usually WGS84)
After the header — three sections:
Waypoints — individual map points (e.g., "Parking", "Spring", "Summit"). Each waypoint has: - Latitude (float, degrees) - Longitude (float, degrees) - Altitude (float, meters above sea level) - Time (Unix timestamp) - Name (string, up to 32 chars) - Comment (string, up to 256 chars) - Icon ID (integer, reference to built-in icon library) - Color (RGB)
Tracks — sequences of trackpoints (GPS receiver passage records). Each track: - Name - Line color - Line type (solid, dashed) - List of trackpoints (lat, lon, alt, time)
Routes — pre-planned routes (different from tracks in that they are manually specified before movement, not recorded). Same structure as tracks.
File size: a typical .gtm with 100 waypoints + 10 tracks of 1000 points each = 50–100 KB. Very compact compared to equivalent GPX (300–500 KB).
Who needs GTM: five roles
Brazilian geologist. Fieldwork in the Serra Canastra mountains or in Amazon rainforests. The geologist records outcrop points with descriptions on a GPS receiver. At home loads .gtm into GPS Track Maker, checks match against the geological map, prints carta for the report. For a Brazilian geologist this is still the standard workflow.
Field biologist. Biodiversity researchers (WWF, Conservation International, government nature-protection agencies) use GPS to log observed species locations. In Brazil, Paraguay, Bolivia GPS Track Maker is still more widespread than alternatives, so .gtm is the format for expedition archives from 1996–2015.
Vintage-GPS collector. A community of people who keep Garmin GPS 12, eTrex Vista, Magellan Meridian, Trimble GeoExplorer running — several thousand worldwide. These devices don't speak GPX (the format appeared later) but accept NMEA-2000 or proprietary Garmin/Magellan formats. GPS Track Maker can convert GPX → GTM → upload via RS-232.
Tourist with cheap GPS receiver. In the 2010s many cheap Chinese GPS receivers (eBay) appeared with firmware mimicking Garmin or Magellan. Most such devices understand GTM better than GPX since their firmware was copied from old Garmin.
Latin America geodata archivist. A scientist or historian assembling an archive of Brazilian field research from the 1990s–2000s will receive many .gtm files. Reading them with modern tools requires GPS Track Maker or GPSBabel.
Software for GTM: five tools
GPS Track Maker. Native format implementation by the author. Free, Windows. Supports reading, editing, exporting, exchange with GPS receivers via RS-232 and USB. Latin-American interface in Portuguese + English + Spanish. gpstm.com
GPSBabel. Command line for conversion between hundreds of GPS formats. One of the most useful open-source tools in the GPS industry. Convert GPX → GTM:
gpsbabel -i gpx -f track.gpx -o gtm -F track.gtm
Reverse direction analogous. Free, cross-platform. gpsbabel.org
QGIS with GPSBabel plugin. Open-source GIS can import .gtm through a built-in wrapper around GPSBabel. Free. qgis.org
OsmAnd. Mobile OSM-map app can import .gtm via GPSBabel (requires Android Termux or iOS Shortcuts). Not the simplest path but it works. osmand.net
Magellan VantagePoint. Paid (~$50), Windows. Native Magellan tool for working with their GPS receivers. Imports .gtm as one of legacy formats. magellangps.com
Pitfalls and tips
Proprietary but documented format. GPS Track Maker is freeware but not open-source. Nonetheless author Odilon Ferreira published the .gtm format specification at gpstm.com. GPSBabel is implemented based on this spec.
Old-device size limits. Magellan Meridian Gold (2002) accepts no more than 500 waypoints per file. Garmin GPS 12 (1996) — 500 waypoints, 20 routes, 1024 trackpoints. If your route is larger — you have to split into multiple .gtm files. GPSBabel automates this via --track-pause-spt and similar options.
Coordinate system is always WGS84. GTM works only with WGS84 (EPSG:4326). If your source data is in UTM or another projection — conversion to WGS84 is required before saving as .gtm. Modern GPS receivers work in WGS84 only — this isn't a limitation.
Waypoint icons aren't portable. GTM stores waypoint icon ID (e.g., "23 = red triangle"), but these IDs map to the built-in library of the GPS Track Maker program. Open .gtm in Garmin or OsmAnd and icons are lost. Store semantic info in Name/Comment fields.
Language support. Old GPS Track Maker versions (pre-7.0) stored Russian, Chinese, Japanese symbols as garbage. After 2010 — Unicode UTF-8. If you open a 2000s .gtm and see gibberish — that context is lost, not recoverable.
RS-232 cable. To connect a vintage GPS receiver to a modern laptop you need a USB-to-RS-232 cable. Not all cables work equally; Prolific PL-2303 chipset is recommended. Without the right driver data transfer won't work.
Time zone bugs. Old GTM versions stored timestamps without time zone, giving a 3-hour shift for Brazilian users (Brasília = UTC-3). When importing old .gtm into modern tools — verify timestamps.
GPX alternative. If your goal is GPS data exchange in 2026, GPX is the better choice. GTM makes sense only if: (a) your target device is vintage GPS, (b) your counterpart uses GPS Track Maker, (c) you have a 1990–2000s file archive.
How to convert OSM to GTM via osm2cdr.ru
osm2cdr.ru doesn't export directly to GTM, but through an intermediate GPX (natively supported) the conversion is simple.
Step 1. On osm2cdr.ru outline the route of interest. For example, a hiking trail through Sochi park. Export the highway=path or route=hiking layer to GPX.
Step 2. Download the GPX file. Open in any text editor to verify — should have <wpt> (waypoints) and <trk> (tracks) tags.
Step 3. Install GPSBabel. Linux: sudo apt install gpsbabel. macOS: brew install gpsbabel. Windows: gpsbabel.org/download.html.
Step 4. Convert:
gpsbabel -i gpx -f sochi_trek.gpx -o gtm -F sochi_trek.gtm
You get sochi_trek.gtm ready for upload.
Step 5. Upload to device. For GPS Track Maker desktop: File → Open → select .gtm, see your track on the Brazil map. For Magellan eXplorist: connect via USB, run Magellan VantagePoint, import .gtm, send to device.
Alternative via GPS Track Maker GUI instead of command line:
- Launch GPS Track Maker
- File → Open Foreign File → select .gpx
- File → Save As → name as .gtm
- Done
For batch processing many routes (e.g., a hiking-club series) — bash script via GPSBabel.
Related formats and resources
- GPX — modern open standard for GPS tracks
- Garmin IMG — main format for Garmin navigators
- KML — Google Earth track format
- FIT — Garmin Fitness Tracker format for sports tracks
- TCX — Garmin Training Center XML
Sources
- GPS Track Maker official site — gpstm.com
- GTM file format specification — gpstm.com/eng/files_eng.php
- GPSBabel GTM driver documentation — gpsbabel.org/htmldoc-development/fmt_gtm.html
- Odilon Ferreira interview, Veja magazine 2008 (Portuguese) — archived
- Wikipedia, GPS Track Maker — pt.wikipedia.org/wiki/GPS_Track_Maker
- GPS hardware compatibility list — gpsbabel docs