Create a georeference

Georeference name:

Type a new name for the georeference. In case of a georeference which will be used for multiple raster maps of the same size and of the same area, it is advised to enter a georeference name that applies to all maps (e.g. the name of the study area).

Description:

Type a description for the georeference. The description is visible on the status bar of the Main window when moving the mouse pointer over the georeference in the Catalog.

Georef Corners:

Select Georef Corners to create a North-oriented georeference, for example when rasterizing point, segment or polygon maps, or for the output of a Resampling operation.

Georef Tiepoints:

Select Georef Tiepoints when you want to add coordinates to a satellite image or to a scanned photograph and when you do not have a DTM. This type of georeference can be used to add coordinates to satellite imagery and for subsequent screen digitizing or to resample the image to another georeference (e.g. to a georef corners).

Georef Direct Linear:

Select Georef Direct Linear when you want to add coordinates to a scanned photograph which was taken with a normal camera, and when you have an existing DTM to also correct for tilt and relief displacement (Direct Linear Transformation). This type of georeference can for instance be used to add coordinates to small format aerial photographs and for subsequent screen digitizing or to resample the photograph to another georeference (e.g. to a georef corners).

Georef OrthoPhoto:

Select Georef Orthophoto when you want to add coordinates to a scanned aerial photograph with fiducial marks, taken with a photogrammetric camera with known principal distance, and when you have an existing DTM to also correct for tilt and relief displacement (Differential rectification). This type of georeference can be used to add coordinates to professional near vertical aerial photographs and further monoplotting on the photograph or for creating an orthophoto (resampling).

Georef 3D display:

Select Georef 3D when you want to make a three-dimensional picture of your study area using a Digital Elevation Model.

Coordinate system:

Select a coordinate system in which this georeference fits. If you do not have a coordinate system yet, it is advised to create one first. To create a coordinate system, click the create button next to this list box or select the Create Coordinate System command from the File menu in the Main window: the Create Coordinate System dialog box will appear.

Pixel size:

Type a pixel size for the new raster map. When you specify for instance 20, the size of each pixel in the raster map will be 20 x 20 m.

Map boundaries:

When an existing coordinate system is selected, the boundary Xmin, Ymin, Xmax and Ymax values of the map are already filled out as defaults. Or type the minimum and maximum X and Y values yourself.

Centers:

Select this check box if the four boundary values (Xmin, Ymin, Xmax, Ymax) of this map should refer to the centers of the four corner pixels of the map.
Clear this check box if the four boundary values should refer to the outer corners of the four corner pixels of this map.

Coordinate system:

Select a coordinate system in which this georeference fits. If you do not have a coordinate system yet, it is advised to create one first. To create a coordinate system, click the create button or select the Create Coordinate System command from the File menu in the Main window.

Background Map:

Select a map list (advised for satellite images), a single band of a satellite image, a color composite, or a scanned photograph that will be displayed in the Tiepoint editor and on which you will position the tiepoints. The background map will directly use the georeference which you are creating.

When you use a map list as a background map, and when the georeference is opened, the map list will be shown as an interactive color composite. After adding tiepoints, the newly created georeference tiepoints is automatically added to all raster maps in the map list.

Background Map:

Select the scanned aerial photograph that will be displayed in the Tiepoint editor and on which you will position the tiepoints. The background map will directly use the georeference which you are creating.

DTM:

Select an existing Digital Terrain Model (DTM), also called a Digital Elevation Model (DEM), from which the height values will be used. Pixel size and accuracy of the DTM are of great importance.

Tip: For a correct behaviour of a georef direct linear or a georef orthophoto, it is essential that you have marked the 'Interpolation' check box in the Properties dialog box of your DTM raster map. For more information, refer to the Raster Map Properties dialog box. Furthermore, the tiepoints of a georef direct linear may not be coplanar, i.e. lie in one (tilted) plane. For more information, see ILWIS objects: georeference direct linear.

Rows Columns:

Type values for the size of the map window in which the three-dimensional view will be displayed or accept the default values. Values refer to screen pixels.

DTM:

Select a raster map with height values (Digital Terrain Model or Digital Elevation Model) which is used to construct the three-dimensional view. For more information on creating a DTM/DEM and a 3D view, see How to calculate a Digital Elevation Model.