Line Number Sample Value Meaning
Line 1 +6.00 Cell size in the X direction
Line 2 -0.00 Rotation in the X direction
Line 3 -0.00 Rotation in the Y direction
Line 4 -6.00 Cell size in the Y direction
Line 5 1709053.00 Easting value of insertion point X
Line 6 807714.00 Northing value of insertion point Y
TIFF World File (TFW) format is supported by ArcView, ArcInfo, MapInfo, and many other programs–such as SMS. TIFF World files are normal TIFF files with an accompanying .twf metadata file. Despite the fact that TWF files are relatively common, the definition of the .twf file has remained obscure.
The TFW file contains information about the origin (insertion point) of the image and individual cell size. There is no information on image dimensions (number of rows or columns), units, projection or datum. This additional information must be obtained from the supplied supplementary information, image description or image supplier, in order to create an accompanying .IF file to correctly georeference the image. Typically, a MapInfo or ESRI image file will be stored in a projection such as NAD27 and California State Plane Zone 6.
A TFW file normally contains the following information:
Line Number Sample Value Meaning
Line 1 +6.00 Cell size in the X direction
Line 2 -0.00 Rotation in the X direction
Line 3 -0.00 Rotation in the Y direction
Line 4 -6.00 Cell size in the Y direction
Line 5 1709053.00 Easting value of insertion point X
Line 6 807714.00 Northing value of insertion point Y
Note that sign of the cell size in Y (line 4) defines if the image insertion point is the upper left or lower left corner. A positive means the “Y” values are increasing upwards and therefore, the registration must be starting at the bottom or lower left corner. A negative sign means that the insertion point is the upper left. The insertion point coordinates relate to the map corner of the image in its defined projection itself.
A sample TWF file is shown below:
2.5 pixel x size (meters)
-0.0 rotation factor
-0.0 rotation factor
-2.5 pixel y size (meters)
75000 image min x (meters) (NW
-200000 image max y (meters) Corner)
Normally an image will be supplied with a .tif and .twf file pair (e.g., RIVER.TIF and RIVER.TFW).
Note that SMS will perform a coordinate transformation of the image. Select Edit | Coordinate Conversions. Note that if only the TIFF image is loaded, then you will not be able to “find” the image. So, it is best that you draw a box around the image to see it.
Also, both the DEM and TFW files will need to be in the same coordinate system (or individually converted) for them to match up in SMS. Hope that this information helps you.