[gdal-dev] General Questions about gdal usage with Grib1 Data Set

[Frank Warmerdam]

Cassanova, Bill wrote:
> I had considered that but was a little concerned about accuracy.  So for
> example:
> 
> Original lat-lon point --> -77.78, 36.01
> Extracted i-j          --> 1015.63, 404.964
> 
> The 4 closest are the ceil/floor of both so:
> 1015 and 1016 for X and 404 and 405 for Y. 
> 
> However, the resolution of the data is 12km.  So.  It would seem more
> accurate to reverse transform the 1015 and 1016 and 404 and 405
> Back to lat-lon, and then determine separation in degrees as opposed to
> rounded off mid-points in raster space.  Does this make sense or is my
> relative newness to GIS beginning to show?

Bill,

I don't see that the distances are likely to be more meaningful
in decimal degrees than in pixels.  If you wanted to do something
really accurate you would need to compute the distances in a locally
accurate projected coordinate system.

> Regardless it seems like what I am suggesting should be possible is I
> set up the backward projection correctly...Right?

Yes

Best regards,
-- 
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