A GeoCoord element is a container for specifiying geographical coordinates for a railway infrastructure object. Thus, a GeoCoord element defines exactly one point on earth given by either two or three dimensional coordinates.
By default, the coordinates shall be given in the reference system WGS84, because it is valid worldwide. WGS84: see http://spatialreference.org/ref/epsg/wgs-84 (external link).
Implementation in railML®
There are some aspects about geographical coordinates and the current implementation in railML, which are not yet solved and require further discussion. These aspects are listed below:
- At the moment, only one <geoCoord> per element can be defined. It is not possible, to give one point multiple geographical coordinates, e.g. for locating a point in different reference systems.
- At the moment, height coordinates cannot exist without horizontal coordinates. From the timetable's perspective this is difficult since often coordinates are not know and only the vertical height/gradient profile could be modelled. Therefore, the height coordinates should be defined independent from the horizontal coordinates. Until then, please use the parameter extraHeight in combination with zero horizontal coordinates (example for German DHHN92):
<geoCoord coord="0 0 0" extraHeight="123.4" epsgCode="urn:ogc:def:crs:EPSG::5783" />
- The height coordinates may differ in various countries referencing different national peils (Amsterdam's Peil, Kronstadt Peil, ...). The peil systems are categorized in the EPSG code too. You may find the EPSG codes at the website of EPSG Geodetic Parameter Dataset (external link).
This code example defines the position of Oslo Sentralstasjon in WGS84 coordinates:
<geoCoord coord="59.911 10.754" epsgCode="4326" />
This code example defines the position of Oslo Sentralstasjon in ETRS89 / ETRS-TM32:
<geoCoord coord="598059.6081 6642972.5966" epsgCode="3044" />