gpx

The gpx library provides predicates for parsing, generating, and validating GPX 1.1 documents. GPX is an XML interchange format for GPS waypoints, routes, and tracks. Coordinates use the WGS84 datum and measurements use metric units.

• https://www.topografix.com/gpx.asp

• https://www.topografix.com/GPX/1/1/

The library uses the dates library for Gregorian calendar validation and the contributed xml_parser library for portable XML parsing and generation. GPX structure and scalar constraints are checked directly; there is no dependency on an XSD processor.

API documentation

Open the ../../apis/library_index.html#gpx link in a web browser.

Loading

To load all entities in this library, load the loader.lgt file:

| ?- logtalk_load(gpx(loader)).

Testing

To test this library predicates, load the tester.lgt file:

| ?- logtalk_load(gpx(tester)).

Representation

A document is represented by the term gpx(Creator, Properties). The GPX version is always 1.1 and is therefore not repeated in the native term. Root properties are:

• metadata(metadata(Properties))

• waypoints(Waypoints)

• routes(Routes)

• tracks(Tracks)

• extensions(XMLNodes)

Points are represented by waypoint(geographic(Latitude, Longitude), Properties). The same point term is used for standalone waypoints, route points, and track points. Point properties include elevation/1, time/1, magnetic_variation/1, geoid_height/1, name/1, comment/1, description/1, source/1, links/1, symbol/1, type/1, fix/1, satellites/1, hdop/1, vdop/1, pdop/1, age_of_dgps_data/1, dgps_station/1, and extensions/1.

Routes and tracks use these terms:

• route(Points, Properties)

• track(Segments, Properties)

• track_segment(Points, Properties)

Nested metadata values use person(Properties), email(Id, Domain), copyright(Author, Properties), link(Href, Properties), and bounds(MinLatitude, MinLongitude, MaxLatitude, MaxLongitude) terms.

Optional values are omitted from property lists. Property order is ignored when validating or generating a document. Generated XML always follows the element order required by the GPX 1.1 schema; parsing also rejects elements in an invalid order.

The time/1 values are atoms using the XML Schema 1.0 dateTime lexical space. Calendar dates, leap years and seconds, fractional seconds, the special 24:00:00 representation, expanded and negative years, and time zones up to 14:00 are validated without changing the original atom. Copyright year/1 values similarly use the XML Schema 1.0 gYear lexical space. In both types, year zero is invalid and expanded years cannot have leading zeroes.

Validation errors

The validate/2 predicate returns all detected errors. Every reason term ends in a path from the GPX root to the failing value. List indexes are zero-based; for example, [tracks,0,segments,1,points,3,time] identifies the time property of the fourth point in the second segment of the first track.

Reasons distinguish malformed native terms, creators, property and value lists, scalar values and ranges, date/time and year lexical values, bounds, extensions, duplicate properties, and unknown properties. See the gpx_protocol API documentation for the complete reason-term vocabulary.

Extensions

Children of GPX extensions elements are preserved using the xml_parser native XML terms. Their top-level elements must use a namespace other than the GPX namespace. Namespace URIs, prefixes, attributes, text, and nested content are preserved across parse and generate operations.

Extension schemas are not interpreted or validated. This corresponds to the portable part of the GPX schema extension contract; its XSD processContents="lax" behavior would require an XSD processor.