GPS Exchange Format
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The GPS Exchange Format (GPX ) is a data format for storing spatial data ( GPS data ), which was developed by the company TopoGrafix. It is based on the general XML standard. An XML Schema describes the elements and the structure of the GPS Exchange format. As file extension is an acronym. Gpx used.
The GPS Exchange Format is an open, royalty-free format that may be used by anyone free of charge. It will facilitate the sharing of spatial data between different programs. Many attributes show similarities to the NMEA 0183 standard.
Properties of GPS data
The XML schema for GPX standard defines only a few data types and tags. In addition to metadata, such as author and description, most GPS receiver mainly supply data for waypoints, routes and track logs (see below).
The geo coordinates latitude, longitude and altitude of a waypoint refer to the WGS84 reference ellipsoid. A position information in GPX format is specified in degrees with decimals instead of degrees and degrees minutes seconds. A meter at the equator corresponds to approximately 0.000 ° '01. As a rule of thumb that the sixth decimal place indicates an accuracy in the decimeter; Data with two decimal places are in the kilometer range. Height shall be given in meters.
Compared with the known ESRI Shapefile format GPX has the advantage that the data is in a readable for the human form; However, this results in a considerably higher memory requirements. In addition, various data types ( points, tracks, etc.) can be stored in a single GPX file.
A GPX file can be validated. It checks whether the structure of the file follows the rules defined in the XML schema and is therefore valid. Currently, the XML schema of the GPX format is available in version 1.1.
A GPX file consists of the coordinates and their description. By type are distinguished:
In one file, all three types can be listed (even each multiple times).
The basic structure is as follows, with UTF -8 encoded data is at the beginning of the file with a byte order mark to be expected:
xml version = " 1.0" encoding = "UTF -8" standalone = "no"? >
Following GPX example shows the main elements of the basis of the positions of the Parliament Building of Germany, Austria and Switzerland:
As a dialect of XML allows the GPX format, embed your own extensions, which are not part of the GPX schema. One example is the GPX Extensions of Garmin.