[Freegis-list] TFW format

[Bill Thoen]

On Thu, Oct 06, 2005 at 04:12:01PM +0200, Petr wrote:
> i need help with tfw format. I have tiff image and tfw file with 
> description:
> 200.00000000
> 0.00000000
> 0.00000000
> -200.00000000
> 3408200.0000
> 5635500.0000
> 
> I searched internet and not found any information about using of this map.

Googling on "tfw format" I found the following on
http://www.asmail.be/msg0055111818.html:
---
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.
---

Also, the GeoTIFF format spec can be found at:
http://www.remotesensing.org/geotiff/spec/geotiffhome.html


> I need transform standard GPS coordinate (eg.: 50d04m55sN 14d26m03sE) to 
> pixel coordinate in my map (eg.: 256px,414px aproximately) and backwards.

Unfortunately, knowing the TFW format won't help you with converting your
GPS coordinate. The TFW file doesn't contain coordinate system information,
so you don't know the projection method, datum, etc.  But once you convert
it into the same system used in your TIFF file, the tfw parameters can be
used to locate it on your image accurately. 
 
- Bill Thoen