[Gdal-dev] creating a BMNG world file

[Frank Warmerdam]

Matt Wilkie wrote:
> Hi there,
> 
> I'm trying to create a valid world file for Blue Marble Next Generation 
> 500m resolution png's. From reading the docs, I've created one for the 
> A1 tile which looks like:
> 
>         0.004166666667
>         0.0000000000
>         0.0000000000
>         -0.004166666667
>         -180
>         90
> 
> and when I load one of those images up with other data, it looks like 
> it's in the right place. However when I use gdal_translate to convert it 
> to 1% of original size the Lat/Long insertion point changes:
> 
>     0.4166666667
>     0.0000000000
>     0.0000000000
>     -0.4166666667
>     -179.7937500000
>     89.7937500000
> 
> is this right? Or should the starting lat-long be offset by half a pixel 
> width (and in what direction?)?

Matt,

The insertion point listed in the world file is the center of the top left
pixel.  So your initial file likely ought to be offset by half a pixel.   But
based on this, as the resolution drops, the insertion point will continue to
move.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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