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tecnica:gps_cartografia_gis:gpx

The GPX format

GPX is the GPS exchange format, you can find information about it at http://www.topografix.com/gpx.asp. In GPX files all coordinates are relative to the WGS84 datum, all measurements are in metric units.

Here are some notes on GPX files downloaded with GPSBabel Version 1.2.3 from a Garmin Foretrex 201 GPS.

Waypoints

This is an example of a saved waypoint:

<wpt lat="43.148408839" lon="10.853555845">
  <ele>74.387085</ele>
  <name>020</name>
  <cmt>020</cmt>
  <desc>020</desc>
  <sym>Flag</sym>
</wpt>

Each field is described by the GPX schema:

lat decimal -90.0 ⇐ value ⇐ 90.0 The latitude of the point. Decimal degrees, WGS84 datum.
lon decimal -180.0 ⇐ value < 180.0 The longitude of the point. Decimal degrees, WGS84 datum.
ele Elevation (in meters) of the point.
name The GPS name of the waypoint. This field will be transferred to and from the GPS. GPX does not place restrictions on the length of this field or the characters contained in it. It is up to the receiving application to validate the field before sending it to the GPS.
cmt GPS waypoint comment. Sent to GPS as comment.
desc A text description of the element. Holds additional information about the element intended for the user, not the GPS.
sym Text of GPS symbol name. For interchange with other programs, use the exact spelling of the symbol as displayed on the GPS. If the GPS abbreviates words, spell them out.

Tracks

This is an example of a saved track:

<trk>
  <name>ACTIVE LOG</name>
<trkseg>
<trkpt lat="43.858259" lon="11.097178">
<ele>66.468262</ele>
<time>2005-03-20T07:20:37Z</time>
</trkpt>
<trkpt lat="43.858280" lon="11.097243">
<ele>40.032104</ele>
<time>2005-03-20T07:20:49Z</time>
</trkpt>
<trkpt lat="43.858280" lon="11.097114">
<ele>40.512817</ele>
<time>2005-03-20T07:20:57Z</time>
</trkpt>
</trkseg>
</trk>
trk A list of tracks.
trkseg A Track Segment holds a list of Track Points which are logically connected in order. To represent a single GPS track where GPS reception was lost, or the GPS receiver was turned off, start a new Track Segment for each continuous span of track data.
trkpt A Track Point holds the coordinates, elevation, timestamp, and metadata for a single point in a track.
lat decimal -90.0 ⇐ value ⇐ 90.0 The latitude of the point. Decimal degrees, WGS84 datum.
lon decimal -180.0 ⇐ value < 180.0 The longitude of the point. Decimal degrees, WGS84 datum.
ele Elevation (in meters) of the point.
time The time that the point was recorded. Date and time in are in Univeral Coordinated Time (UTC), not local time! Conforms to ISO 8601 specification for date/time representation. Fractional seconds are allowed for millisecond timing in tracklogs.

Timestamps

Date and time in are in Univeral Coordinated Time (UTC), not local time! Conforms to ISO 8601 specification for date/time representation.

From http://www.cl.cam.ac.uk/~mgk25/iso-time.html:

  • The international standard date notation is YYYY-MM-DD
  • The international standard notation for the time of day is hh:mm:ss

If a date and a time are displayed on the same line, then always write the date in front of the time. If a date and a time value are stored together in a single data field, then ISO 8601 suggests that they should be separated by a latin capital letter T, as in 1995-12-31T23:59:59.

Without any further additions, a date and time as written above is assumed to be in some local time zone. In order to indicate that a time is measured in Universal Time (UTC), you can append a capital letter Z to a time as in 23:59:59Z or 2359Z

Note: The Z stands for the zero meridian, which goes through Greenwich in London, and it is also commonly used in radio communication where it is pronounced Zulu (the word for Z in the international radio alphabet). Universal Time (sometimes also called Zulu Time) was called Greenwich Mean Time (GMT) before 1972, however this term should no longer be used. Since the introduction of an international atomic time scale, almost all existing civil time zones are now related to UTC, which is slightly different from the old and now unused GMT.

tecnica/gps_cartografia_gis/gpx.txt · Last modified: 2005/10/19 22:31 (external edit)