If a raster graphic background is to be included in Visum, georeferencing the background in the network can be executed automatically when, in addition to the actual graphic file (for example Background.jpg), a so-called World file (for example Background.jpw) is available, which contains the data for georeferencing the image file. If a World file is available, this makes the exchange and including backgrounds much easier, because the background is automatically inserted in the right position in Visum. The effort for vernier adjustment of the background does therefore not apply.
A World file contains the transformation information used by the image, for the reference to world coordinates. The format was specified and introduced by ESRI. The naming convention for World files provides, that the last letter of the file ending of the graphic file is replaced with a w, the rest of the file name corresponds to the respective graphic file (if the graphic is named Map.tif for example, the respective World file is then named Map.tiw). A World file describes the coordinates, the scale and the rotation of the background.
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Note: World files do not contain a reference to a coordinate system. |
Each World file has six rows. The Table 291 shows an example for a World file.
- Row 1: Parameter A pixel size in x direction
- Row 2: Parameter D rotation about y axis
- Row 3: Parameter B rotation about x axis
- Row 4: Parameter E pixel size in y direction
- Row 5: X coordinate of the upper left pixel of the background
- Row 6: Y coordinate of the upper left pixel of the background
32.0 0.0 0.0 -32.0 691200.0 4576000.0 |
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Note: Georeferencing and thus creating the World file can be executed with GIS software (for example ArcGIS by ESRI). Because the World file is a text file, it is theoretically possible to create it yourself in the text editor if the necessary information is known. |
