[Freegis-list] TFW format

[Petr]

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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