[GRASSLIST:5332] Re: Core dump on Winkle Triple projection

cheg01 at attbi.com cheg01 at attbi.com
Sun Jan 19 14:46:40 EST 2003


----- Original Message -----
From: "Glynn Clements" <glynn.clements at virgin.net>
To: <cheg01 at attbi.com>
Cc: <grasslist at baylor.edu>
Sent: Saturday, January 18, 2003 10:40 PM
Subject: Re: [GRASSLIST:5330] Re: Core dump on Winkle Triple projection


> >
> Note that r.proj works "in reverse". IOW, for each cell in the
> destination location, it transforms the coordinates of the cell's
> centre using the *inverse* projection, to get a coordinate in the
> source location. It then reads the value of the cell at that
> coordinate from the source raster, and stores the value in the
> original cell in the destination location.
>

I understand, because the destination map can have any arbitrary resolution
you have to lookup or interpolate the value in the source map for a given
cell location in the destination map.


> Ultimately, if you want to project into a location whose projection
> doesn't have a defined inverse, you will have to convert to sites
> project that (s.proj/v.proj use the forward projection), then convert
> back to raster.

This way the projection is independent of the resolution of the destination
map.


>
> --
> Glynn Clements <glynn.clements at virgin.net>




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