Message-ID: A5E327808C88D211A76700A0C9D3A3D511A502@HERMES
To: tiff@olympiakos.com
Subject: RE: .tfw format
From: Geoff Vandegrift <gvandegrift@hsgt.com>
Date: Mon, 13 Sep 1999 09:22:20 -0600
Cc: James McMullen <james@iiMap.com>, Mario Boratto <boratto@brhs.com.br>
Sender: owner-tiff@olympiakos.com

Title: RE: .tfw format

TFW has been a thorn in my side for quite some time.  All of our users expect support for TFW; but until recently, the only "specification" we had for the format was in legacy source code.

From two different sources (ArcView help files and a contact at ESRI) I have recently been informed that the items in the TFW file are actually supposed to be the non-trivial elements from a 2D, affine transformation matrix:

/ A B C \
| D E F |
\ 0 0 1 /

Using the symbols above, the TFW file is organized as follows:

A
D
B
E
C
F

I have yet to see a sample tfw file where the B and D terms are non-zero (indicating rotation).  In fact, the ArcView help files say that rotation is not supported.

It turns out that our interpretation (i.e., the legacy code) of rotation has been wrong all along, but we were okay because no one seems to ever use rotation in tfw.

If anyone has anything to add to this, I would be extremely interested.

Geoff Vandegrift
Senior Software Developer
Hitachi Software Global Technology, Ltd.

> -----Original Message-----
> From: James McMullen [mailto:james@iiMap.com]
> Sent: Saturday, September 11, 1999 12:01 AM
> To: Mario Boratto; tiff@olympiakos.com
> Subject: Re: .tfw format
>
>
> 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
>
>
