[GRASSLIST:8002] Re: r.proj takes a very long time / does not complete

Morten Hulden morten at untamo.net
Sat Aug 20 09:38:28 EDT 2005

> On 8/19/05, Jason Horn <jhorn at bu.edu> wrote:

>>I'll try your idea of projecting the 4 corners,
>>and then computing the resolution.  One question, isn't this what
>>r.proj would do anyway?

Not really. r.proj is "region aware", i.e. will use the resolution of 
your current region no matter what the resolution of the input map is. 
That is why you should check that you really have the desired resolution 
set before running r.proj.

In the projection process the center of each cell in your current region 
will be projected onto the input map and the value of the nearest 
neighbor (if you use this default method) will be extracted. This value 
will then become the value of the corresponding cell(s) in the output map.

As a consequence the output map grid will be aligned with other maps in 
your location, which may be essential for further analysis and 
processing with some other Grass modules. The alternative, reprojecting 
with gdalwarp, does not as far as I know take the cell grid of your 
current region into account.


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