Create objects: Coordinate system

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Boundary only coordinate system Projected Coordinate system Geographic coordinate system
Create coordinate system

A coordinate system contains information on the kind of coordinates used in a map. You may for instance use user-defined coordinates, coordinates defined by a national standard or coordinates of a certain UTM zone. A coordinate system defines the possible XY- or LatLon-coordinates that can be used in maps. Feature coverages such as point, segment and polygon have always a coordinate system. Raster coverage, on the other hand, have a georeference which uses a coordinate system. In other words, a coordinate system is a service object used by feature coverages and georeferences. In ILWIS, XY-coordinates are in meters and the 90 angle between the positive X-axis and the positive Y-axis.

Coordinate system types
There are five main types of coordinate systems:

  • Boundary only coordinate system: to define XY-coordinates for maps by only specifying the boundaries of your study area. This type of coordinate system should only be used when you are sure that you will not use projections at all; furthermore, maps using a coordinate system boundary only, cannot be transformed into any other coordinate system.
  • Projected coordinate system: to define XY-coordinates for maps by specifying the boundaries of your study area and when you want to have the possibility to add projection information, ellipsoid information and/or datum information. You can add the projection information later on or right away. Maps with different coordinate systems and different projections can be transformed into one another.
  • Geographic (Latlon) coordinate system: to define LatLon-coordinates for maps by specifying the boundaries of your study area in Latitudes and Longitudes and when you want to have the possibility to add ellipsoid information and/or datum information. You can add the ellipsoid information and/or datum information later on or right away. Coordinate systems of type Latlon are suitable to store data; for display and/or printing purposes (map view and layout), it is advised to use a coordinate system of type projection in a map window.
  • Coordinate system formula: when you obtained data which is using different XY-coordinates than the coordinate system of your project, and when you know the relation between the two coordinate systems. You can create a coordinate system formula for maps with artificial coordinates, i.e. starting at (0,0) or digitized in millimeters. The coordinate system formula uses a 'related' coordinate system; this is the coordinate system with correct coordinates. When you have defined the formula and when the map with artificial coordinates uses the newly created coordinate system formula, then you can transform the map to the correct coordinate system.
  • Coordinate system tie points: when you obtained data which is using different XY-coordinates than the coordinate system of your project, and when you do not know the relation between the two coordinate systems. You can create a coordinate system tiepoints for maps with artificial coordinates, i.e. starting at (0,0) or digitized in millimeters. The coordinate system tiepoints uses a 'related' coordinate system; this is the coordinate system with correct coordinates. When you have specified the tiepoints and transformation method, and when the map with artificial coordinates uses the newly created coordinate system tiepoints, then you can transform the map to the correct coordinate system.

Furthermore, two coordinate systems are available in the system Catalog and one which is used internally:

  • Unknown; used when a map coordinate is unknown or map coordinates is not important to users.
  • Latlon; used when you raster or vector data are on a sphere such as world coverage.
  • Differential; is only available internally and defined by the Variogram surface operation. This coordinate system is incompatible with any other coordinate system and is not available to be used by users.