1999.09.11 06:01 "Re: .tfw format", by James McMullen
This is surprisingly obscure information, considering how widely used TFW is.
A web search turned up only a dead link into ESRI; no doubt the official definition is there somewhere. AFAIK, TFW says nothing about units or projection; you just have to know that a particular file is, say, NAD27 California State Plane Zone 6.
The following is from the good folks at ER Mapper, with whom I have no affiliation:
Q34. Can ER Mapper use TIFF World files (TFW)?"
A. The TFW file was created to give spatial location to the massive amounts of imagery that is traded around in TIFF, which does not carry any coordinate information on it's own.
In a directory structure, the TFW file will have the same name as the TIFF it is referencing as in this example:
The TFW structure is extemely simple. It is a 6 line file that can be opened up and read in any text editor such as WordPad or Notepad in Windows. A sample TFW file opened up would look like:
Line 1 - Cell size in the "X" direction
Line 2 - Insertion point in the "X" direction
Line 3 - Insertion point in the "Y" direction
Line 4 - Cell size in the "Y" direction
Line 5 - Easting value of insertion point "X"
Line 6 - Northing value of insertion point "Y"
Note that sign on line 4 will tell you if the 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 corner. Vice-versa for a negative sign.