FAQ: What is the format of the world file used for georeferencing images?
What is the format of the world file used for georeferencing images?
The world file is an ASCII text file associated with an image and contains the following lines:
- Line 1: x-dimension of a pixel in map units
- Line 2: rotation parameter
- Line 3: rotation parameter
- Line 4: NEGATIVE of y-dimension of a pixel in map units
- Line 5: x-coordinate of center of upper left pixel
- Line 6: y-coordinate of center of upper left pixel
If the image lacks a world file, a world file can be created using a text editor. This is generally practical only when the image does not require any rotation or rectification to be properly georeferenced, meaning lines 2 and 3 should be zero. Line 4 is negative to convert from image row numbering (increasing from the top down) to map coordinates (increasing from the bottom up). For a rectified image, line 4 must be equal to line 1 and of opposite sign. The ArcInfo commands REGISTER and RECTIFY, as well as GRIDIMAGE and CONVERTIMAGE create a world file.
The world file must follow this naming convention. If the image file name has a three-character extension (image1.tif), the world file has the same name followed by an extension containing the first and last letters of the image's extension and ending with a 'w' (image1.tfw). If the extension has more or less than three characters, including no extension at all, then the world file name is formed by simply appending a 'w' to the image file name.
The world file is discussed in the ArcInfo Workstation Help documentation under Cartography > Image Integration > Registering an image to real-world coordinates > Georeferencing images.
- How To: Create a world file from a GeoTIFF image using ArcInfo Workstation
- ArcIMS 9.3: Understanding world files
- ArcMap: World files for raster datasets