Message-ID: 37D9F020.12C26BDD@iiMap.com
To: Mario Boratto <boratto@brhs.com.br>, tiff@olympiakos.com
Subject: Re: .tfw format
From: James McMullen <james@iiMap.com>
Date: Fri, 10 Sep 1999 23:01:05 -0700
Organization: iimap
References: <3.0.5.32.19990909084719.00905440@mail.island.net> <37D919A7.DCCD6B96@brhs.com.br>
Sender: owner-tiff@olympiakos.com


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:

                image_x.tif
                image_x.tfw

        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:

                +6.00
                -0.00
                -0.00
                -6.00
                1709053.00
                807714.00

        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.


--
http://www.cityROM.com
james@iimap.com



