DMD HUB GPX Extension

Overview

The DMD HUB GPX Extension (dmd: namespace) embeds pre-computed route data directly inside standard GPX 1.1 files. This eliminates the need for routing API calls, on-device surface extraction, and elevation computation when loading a file — routes display instantly.

The extension is placed inside the <extensions> block of <rte> or <trk> elements and is fully compliant with the GPX 1.1 specification. Applications that don't understand the dmd: namespace will simply ignore it.

Benefits

Schema Structure

Add the namespace declaration to your <gpx> root element:

<gpx version="1.1" creator="YourApp"
     xmlns="http://www.topografix.com/GPX/1/1"
     xmlns:dmd="https://dmdnavigation.com/ns/gpx/1">

The extension is placed inside <rte><extensions> or <trk><extensions>:

<rte>
  <name>My Route</name>
  <extensions>
    <dmd:PreRendered version="1" hash="sha256:abc123..." profile="road-fast-all">
      <dmd:CalculatedRoute>...</dmd:CalculatedRoute>
      <dmd:Instructions>...</dmd:Instructions>
      <dmd:Surface>...</dmd:Surface>
      <dmd:Warnings>...</dmd:Warnings>
      <dmd:Stats .../>
    </dmd:PreRendered>
  </extensions>
  <rtept lat="..." lon="..."></rtept>
</rte>

Element Reference

<dmd:PreRendered>

Root container for all pre-rendered data.

Attribute	Type	Description
version	Integer	Schema version (currently 1). If a reader encounters a higher version, it should fall back to normal routing.
hash	String	Integrity hash. Format: sha256:<16 hex chars>
profile	String	The routing profile used to generate this data (e.g., road-fast-all, offroad-medium)

<dmd:CalculatedRoute>

Routes only (tracks already have <trkpt> geometry). Contains the full routed geometry as a semicolon-separated text node:

<dmd:CalculatedRoute>48.123456,16.456789,312.5;48.123470,16.456900,313.1;...</dmd:CalculatedRoute>

Each point is lat,lon,ele with 6 decimal places for coordinates and 1 for elevation (meters). Whitespace between points is allowed and should be stripped before parsing.

<dmd:Instructions>

Turn-by-turn navigation instructions:

<dmd:Instructions>
  <dmd:I lat="48.123" lon="16.456" type="LEFT" dist="1250" road="Hauptstrasse" ref="B17"/>
  <dmd:I lat="48.200" lon="16.500" type="ROUNDABOUT" dist="3400"/>
  <dmd:I lat="48.300" lon="16.600" type="DESTINATION" dist="5200"/>
</dmd:Instructions>

Attribute	Description
lat, lon	Instruction point coordinates
type	Instruction type enum (see below)
dist	Cumulative distance from route start (meters)
road	Road name (optional)
ref	Road reference number (optional)
dest	Destination sign text (optional)
jref	Junction reference (optional)

Instruction Types:

<dmd:Surface>

Paved/unpaved classification segments:

<dmd:Surface>
  <dmd:S s="0" e="142" sf="asphalt" hw="secondary" p="1"/>
  <dmd:S s="143" e="380" sf="gravel" hw="track" p="0"/>
</dmd:Surface>

Attribute	Description
s	Start point index (into CalculatedRoute or trkpt sequence)
e	End point index (inclusive)
sf	OSM surface tag value (e.g., asphalt, gravel, dirt)
hw	OSM highway tag value (e.g., secondary, track, path)
p	Paved flag: 1 = paved, 0 = unpaved

<dmd:Warnings>

Pre-computed hazard warnings along the route:

<dmd:Warnings>
  <dmd:W type="SLOPE" lat="48.5" lon="16.8" dist="12500" val="18.5"/>
  <dmd:W type="UNPAVED" lat="48.6" lon="16.9" dist="15000" len="3200"/>
</dmd:Warnings>

Attribute	Description
type	SLOPE (gradient ≥ 15%) or UNPAVED (unpaved run ≥ 250m)
lat, lon	Warning location
dist	Cumulative distance from route start (meters)
val	Slope percentage (SLOPE type only)
len	Unpaved section length in meters (UNPAVED type only)

<dmd:Stats>

Aggregate statistics (self-closing element with attributes):

<dmd:Stats dist="185420" gain="2340" loss="2180" eleMin="120" eleMax="1845"
           time="14400" paved="72" maxSlope="22.5" minSlope="-18.3"/>

Attribute	Unit	Description
dist	meters	Total route distance
gain	meters	Total elevation gain
loss	meters	Total elevation loss
eleMin	meters	Minimum elevation
eleMax	meters	Maximum elevation
time	seconds	Estimated travel time
paved	%	Percentage of route that is paved (0–100)
maxSlope	%	Maximum uphill slope
minSlope	%	Maximum downhill slope (negative value)

Integrity Hash

The hash ensures that pre-rendered data matches the current route waypoints. If a file is edited in another application (waypoints moved/added/removed), the hash will not match and readers should discard the pre-rendered data and re-route.

Algorithm

1. Build a canonical string from the source waypoints:

   lat1,lon1;lat2,lon2;...;latN,lonN;profile=road-fast-all

   • For <rte>: use all <rtept> coordinates
   • For <trk>: use all <trkpt> coordinates
   • Coordinates truncated to 6 decimal places
   • Append ;profile= followed by the routing profile string
2. Compute SHA-256 of the canonical string (UTF-8 encoded)
3. Take the first 16 hex characters of the hash
4. Store as: sha256:<16 hex chars>

Reader Behavior

Scenario	Action
Hash matches	Use pre-rendered data directly. No routing needed.
Hash mismatch	Discard pre-rendered data. Route via normal method (DMD Router, etc.)
No hash present	Treat as no pre-rendered data.
Unknown version	Fall back to normal routing.

Implementation Guide

For Readers (GPX Viewers)

1. Parse the GPX file normally (tracks, routes, waypoints)
2. For each <rte> or <trk>, check for <dmd:PreRendered> in <extensions>
3. If found, compute the expected hash from the source coordinates + profile
4. If hash matches: use <dmd:CalculatedRoute> for display geometry, <dmd:Stats> for metadata, etc.
5. If hash doesn't match: ignore the extension and route normally

For Writers (Route Planners / Navigation Apps)

1. After computing a route (via DMD Router or your routing engine), collect:
   • Full routed geometry (the dense point array)
   • Surface/highway classification per segment
   • Turn instructions (if your router provides them)
   • Elevation statistics
2. Compute the hash from the source waypoints + routing profile
3. Write the <dmd:PreRendered> block inside <extensions>
4. Continue writing normal <rtept> / <trkpt> elements as usual

Full Example

<?xml version="1.0" encoding="UTF-8"?>
<gpx version="1.1" creator="DMD HUB GPX Planner"
     xmlns="http://www.topografix.com/GPX/1/1"
     xmlns:dmd="https://dmdnavigation.com/ns/gpx/1">
  <metadata>
    <name>Mountain Loop</name>
  </metadata>
  <rte>
    <name>Route 1</name>
    <extensions>
      <dmd:PreRendered version="1" hash="sha256:f28a213d70082096" profile="offroad-medium">
        <dmd:CalculatedRoute>41.651310,-8.249183,114.5;41.651327,-8.249231,114.3;41.650449,-8.249211,110.8;41.649858,-8.247084,127.0;41.648490,-8.245994,134.5</dmd:CalculatedRoute>
        <dmd:Instructions>
          <dmd:I lat="41.651296" lon="-8.250214" type="SHARP_LEFT" dist="91"/>
          <dmd:I lat="41.648015" lon="-8.245977" type="SLIGHT_RIGHT" dist="658"/>
          <dmd:I lat="41.632462" lon="-8.244647" type="DESTINATION" dist="3980"/>
        </dmd:Instructions>
        <dmd:Surface>
          <dmd:S s="0" e="2" sf="asphalt" hw="tertiary" p="1"/>
          <dmd:S s="3" e="4" sf="" hw="track" p="0"/>
        </dmd:Surface>
        <dmd:Warnings>
          <dmd:W type="SLOPE" lat="41.651274" lon="-8.250075" dist="79" val="15.4"/>
          <dmd:W type="UNPAVED" lat="41.648490" lon="-8.245994" dist="658" len="2364"/>
        </dmd:Warnings>
        <dmd:Stats dist="3980" gain="396" loss="48" eleMin="105.0" eleMax="465.0"
                 time="358" paved="51" maxSlope="33.8" minSlope="-24.9"/>
      </dmd:PreRendered>
    </extensions>
    <rtept lat="41.65131" lon="-8.249183"></rtept>
    <rtept lat="41.632462" lon="-8.244647"></rtept>
  </rte>
</gpx>

Compatibility

The extension is currently supported by:

• DMD HUB GPX Planner (web) — writer + reader
• DMD HUB GPX Browser (web) — reader
• DMD HUB iOS App — reader
• DMD2 Android App — writer + reader

Any GPX application can add support by following the implementation guide above. The extension does not interfere with standard GPX processing — non-supporting apps will simply ignore the dmd: namespace elements.