[Freegis-list] TFW format

[Markus Neteler]

Petr,


maybe this page helps:
http://mpa.itc.it/radim/jtsk/
GIS GRASS a JTSK (Krovak)

Markus


On Fri, Oct 07, 2005 at 07:57:06AM -0600, Bill Thoen wrote:
> 
> Petr,
> 
> Since this list is based in Germany, somebody here should know the details,
> but System 42/83 apppears to be a datum. From
> http://www.killetsoft.de/transdpe.htm I read,  "The former German Democratic
> Republic used the System 42/83 based on a Krassowskij ellipsoid and
> projection into the Gauss-Krueger coordinate system with six degrees
> meridian strips..." The projection sounds like it's essentially UTM but I
> don't know enough of the details to tell you any more than that.
> 
> Then to calculate the pixel position from your TFW parameters:
> 200.00000000
> 0.00000000
> 0.00000000
> -200.00000000
> 3408200.0000
> 5635500.0000
> 
> you subtract the last two parameters from your coordinates (x-3408200,
> y-5635500) and divide the x result by 200 and the y result by -200, and
> that should be the pixel you seek (note: the pixel at 0,0 is at the upper
> left corner of the image.) I'm also assuming that the coordinates are in
> meters. The coordinate listed in your TFW file is the coordinate at the 0,0
> pixel.
> 
> 
> On Fri, Oct 07, 2005 at 10:46:04AM +0200, Petr wrote:
> > S42 coordinate system is described on the web, but i don't know how can i 
> > use it in PROJ.4 or other program.
> > In projections list isn't anything like S42 ;( Maybe it has other name then 
> > S42.
> > 
> > If i convert my coordinate to S42 or get coordinate in S42 system from GPS 
> > what else i need to compute pixel position?
> > What units and begin have values in my TFW file on line 5 and 6? Meters?
> > 
> > Thank you
> > 
> > Peter
> > 
> > Bill Thoen wrote:
> > >Petr wrote:
> > >
> > >>ok, i know that my map is in S-42 coordinate system. what else i need 
> > >>to know to convert GPS coordinate to position in bitmap?
> > >
> > >
> > >You first need to convert your coordinates from degrees, minutes, 
> > >seconds to decimal degrees, and then run them through some sort of 
> > >coordinate conversion software (Try GEO at http://opensourcegis.org/). 
> > >To convert 50d04m55sN 14d26m03sE to decimal degrees, you use the 
> > >following formula: d + m/60 + s/3600 where d is your degrees, m is your 
> > >minutes and s is the seconds. Then if the longitude is west, make your 
> > >longitude negative, and if your latitude is south, make your latitude 
> > >negative. To convert the coordinate you list above to decimal degrees, 
> > >it's longitude is 14 + 26/60 + 3/3600, or 14.4341667, and latitude is 50 
> > >+ 4/60 + 55/3600, or 50.0819444. Then you just need to convert 
> > >(14.4341667, 50.0819444) to S-42 coordinates (and I don't recognize that 
> > >coordinate system, so I can't help you there) with some coordinate  
> > >conversion tool.
> > >
> > >HTH,
> > >- Bill Thoen
> > >
> > >>Thnak you
> > >>
> > >>Bill Thoen wrote:
> > >>
> > >>>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
> > >>
> > >>
> > >>
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> > >>
> > >
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> 
> 

-- 
Markus Neteler     <neteler itc it>       http://mpa.itc.it
ITC-irst -  Centro per la Ricerca Scientifica e Tecnologica
MPBA - Predictive Models for Biol. & Environ. Data Analysis
Via Sommarive, 18        -       38050 Povo (Trento), Italy