A Georeference is a service object, that can be used by one or several raster maps. A georeference defines the relation between rows and columns in a raster map and XY-coordinates. The location of pixels in a raster map is thus defined by a georeference. It is advised that raster maps of the same area use the same georeference. A georeference uses a coordinate system which may contain projection information. Polygon, segment and point maps merely use a coordinate system.
There are five main types of georeferences:
- georeference corners: a North-oriented georeference to be used during rasterization of vector data or as the North-oriented georeference to which you want to resample maps.
- georeference tiepoints: a non-North-oriented georeference to add coordinates to a satellite image or to a scanned photograph, a scanned map, etc. without using a DTM.
- georeference direct linear: to add coordinates to a scanned photograph while using a DTM.
- georeference orthophoto: to add coordinates to a scanned aerial photograph while using a DTM and camera parameters.
- georeference 3D: to create a three dimensional view of maps.
Other types of georeferences are obtained when performing an operation on raster maps which are:
- georeference factor: created by the Spatial Raster Aggregation and the densifyraster operations.
- georeference mirrorrotate: created by the mirrorrotateraster operation.
- georeference submap, submapcorners or submapcoords: created by the Sub-map of raster map and the Glue raster maps operations (not available yet).
- georeference differential: created by the Variogram surface operation (not available yet).
General use of georeferences; when a raster map has a georeference, you can:
- inspect coordinates at the position of the mouse pointer in a map window, at the status bar.
- retrieve information at the position of the mouse pointer in a map window from other maps, i.e. functionality of the pixel information window.
- inspect the pixel size of raster maps in meters.
- check if raster maps fit on top of each other (requirement for MapCalc and Cross).
- overlay vector data on raster maps.
- rasterize vector data to raster maps.
- resample raster data which uses a particular georeference to another georeference; create an orthophoto from a scanned aerial photograph which has a georef orthophoto by resampling it to a georef corners.
- screen digitize on satellite images or on scanned photographs which have a georef tiepoints; screen digitize on scanned photographs which have a georef direct linear; monoplot on scanned aerial photographs which have a georef orthophoto.