[Freegis-list] TFW format
freegis at pbox.cz
Fri Oct 7 10:46:04 CEST 2005
S42 coordinate system is described on the web, but i don't know how can i use it in PROJ.4 or other
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?
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.
> - 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
>>>> I searched internet and not found any information about using of
>>>> this map.
>>> Googling on "tfw format" I found the following on
>>> 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
>>> left or lower left corner. A positive means the "Y" values are
>>> 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:
>>>> 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
>>> GPS coordinate. The TFW file doesn't contain coordinate system
>>> so you don't know the projection method, datum, etc. But once you
>>> 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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