[OSM-talk] How to generate a worldfile for an image

[Andrew]

I don't really know about osmarender - but fairly conventionally there
is a world file format described, amongst other places, here:
http://duff.ess.washington.edu/data/raster/drg/tfw.html

I don't know if osmarender uses that format, but plenty of closed source
and open source spatial software does.  The two lines that you are
trying to get might be the rotation lines - so if there is no rotation
required you just put zeros. 

Mostly people generate these files with software that allows
registration.  Quantum GIS can do this, and most likely GRASS. 
Typically you select four or more points in the image, for which you can
determine real world coordinates in your coordinate system of choice,
and the software builds a best fit transformation, and writes the
corresponding world file. (note that the 'coordinate system of choice'
probably needs to be the same coordinate system used by the data drawn
in the image, ie UTM or geographic or whatever)

hth
Andrew.

Ralf Zimmermann wrote:
> I am looking for practical information on how to create a worldfile 
> (.pgw) for an image (.png) that I created with osmarender.
>
> I know lat/lon of the four corners of the image and the width/height of 
> the image. How do I calculate the values for the six lines of the worldfile?
>
> I spent an hour with Google trying to find good information. But I did 
> not find any practical information how to convert the data.
> Now I am confused.
>
> Does anyone on the list have any practical advise on generating a 
> worldfile with the information I have?
>
> RalfZ
> Munich, Germany
>
>
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