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World Files

A "world file" is a simple text file containing auxilliary georeferencing information for an image. It can be used to georeference an image that has no georeferencing information within it, or to override existing georeferencing information.

By convention, the filename for a world file is the same as the image it pertains to, with a different extension. The three-letter extension is made up of the first and last characters of the image filename extension, followed by a 'w'. For example, the world file for a TIFF image named "bainbridge.tif" would be "bainbridge.tfw"; the world file for a MrSID image named "madison.sid" would be named "madison.sdw".

Generating World Files

Check Generate next to World Files on the General tab of the Preferences dialog box to automatically generate world files upon encoding.

Format

The world file format is six lines, each line containing a double precision value (represented in text). No additional lines may be present. Leading and trailing whitespace are allowed.

The meanings of the six values are:

1. dimension of a pixel in map units in x direction
2. first rotation term
3. second rotation term
4. dimension of a pixel in map units in y direction
5. x-coordinate of the center of the upper-left pixel
6. y-coordinate of the center of the upper-left pixel

The y-dimension is, by convention, a negative value.

GeoExpress ignores the rotation term in most cases.

Example

This is an example of a world file:

  0.20000000

  0.00000000

  0.00000000 

 -0.20000000 

780.10000000 

219.90000000

This world file indicates the image resolution is (0.2, -0.2) and the upper-left is at (780.1, 219.9). The rotation terms are zero, meaning no rotation is required.