How to configure a coordinate system
Geographic coordinate systems are configured with a set of related units.
examples
The following examples shows how to configure the Dutch coordinate system (Rijksdriehoekmeting):
Until 8.7.0 the format property was used instead of SpatialReference.
1) default order of Y, X in point functions, see xy-order:
unit<float32> m := baseunit('m', float32);
unit<fpoint> point_rd_base
: DialogData = "ngr_layer"
, SpatialReference = "EPSG:28992";
unit<fpoint> point_rd := range(point_rd_base, point(300000[m],0[m]), point(625000[m],280000[m]));
2) X, Y order in point functions, see xy-order:
unit<float32> m := baseunit('m', float32);
unit<fpoint> point_rd_base
: DialogData = "ngr_layer"
, SpatialReference = "EPSG:28992";
unit<fpoint> point_rd := range(point_rd_base, point(0[m],300000[m]), point(280000[m],625000[m]));
explanation
Three units are configured:
- m: a baseunit for items with as metric: meter. The coordinates in the Rijksdriehoekmeting are expressed in meters.
- point_rd_base: the coordinate sytem base unit. The SpatialReference property for this unit refers to EPSG:28992, the EPSG code for the Rijksdriehoekmeting. This SpatialReference property is in use for descriptive purposes and can be used for coordinate transformations. The DialogData property for this unit refers to the background layer, in the case a WMS layer.
- point_rd: the coordinate system unit configured with an expression, defining the range of allowed values. The first argument of this range function refers to the coordinate system base unit, relating the set of allowed values to the coordinate system used, in this case: Rijksdriehoekmeting.
If coordinate systems are configured in this way, vector-data with point_rd as values-unit for it’s feature attributes and grid-data related to point_rd can be combined in the same map view. The GeoDMS supports operators-and-functions for coordinate conversions, especially from and to coordinates in the Rijksdriehoekmeting, see geometric-functions.