Image World File

A world file is a plain text file used by geographic information systems to georeference raster map images. Small-scale rectangular raster image maps can have an associated world file for GIS map software which describes the location, scale and rotation of the map. These world files are six-line files with decimal numbers on each line.

World files do not specify a coordinate system.
This information is generally stored in another companion file, the Orbit Resource Descriptor File (ORD)

Structure

An world file is a plain text file used by Orbit to georeference an image file. The world file is always associated with an OMI file : it describes the location, scale and rotation of the map. These world files are six-line files with decimal numbers on each line.

More information can be found on: https://en.wikipedia.org/wiki/World_file.

Create

Create and edit these files using a text editor. Take care of spelling and file syntax.

Parameters

Line 1: pixel size in the x-direction in map units/pixel
Line 2: rotation about y-axis
Line 3: rotation about x-axis
Line 4: pixel size in the y-direction in map units
Line 5: x-coordinate of the center of the upper left pixel
Line 6: y-coordinate of the center of the upper left pixel

Examples of Associated World Files

Format	Image Data File	Image World File
Orbit Multiresolution Image	.omi	.oiw
ECW	.ecw	-
Bitmap	.bmp	.bpw
Graphics Interchange Format	.gif	.gfw
JPEG	.jpg	.jgw
Portable Network Graphics	.png	.pgw
Mister Sid	.sid	.sdw
Tagged Image File Format	.tif(f)	.tfw

http://en.wikipedia.org/wiki/World_file