[GRASSLIST:8571] Re: Changing scale of raster map

[Ian MacMillan]

Bruno, sorry that I misidentified your problem.  I think you are 
looking to use a command like r.neighbors.  I haven't used it much, but 
I think there is a sum function in there that you can use.

G'luck,
Ian

On Oct 10, 2005, at 8:20 AM, Bruno GUILLAUME wrote:

> Ian,
>
> thanks for your prompt reply. Let us talk about my raster, say "toto" 
> (unit=kg).
> Well, in fact, my initial resolution for toto is 00:00:30 but it is 
> full world map (=933120000 grid cells in total!), so it is not easily 
> portable in flat ASCII format!! So, I prefer to convert it first to a 
> resolution of 1°x1° (this resolution is largely enough for my goals).
> The problem is that after using the g.region command to convert it, I 
> check out the conservation of mass and my problem is that I do not get 
> the same total amount of kg (unit of toto) with r.sum rast=toto under 
> 00:00:30 resolution and under 1° resolution !
> So, I suppose that g.region do not accumulate the field of values 
> represented in toto (unit=kg) but rather interpolate it.
> So what does it do exactly ? And how can I get it to change resolution 
> with mass-conservation of the field in toto, so that the value in one 
> big grid cell of toto in 1°x1° resolution be equal to the sum of all 
> little grid cell values (of resolution 00:00:30) comprised in the big 
> cell  ?
>
> Hope this problem is clearer expressed,
>
> Bruno.
>
> Ian MacMillan wrote:
>> Bruno, first thing, in a latlong projection, the units of resolution 
>> are given in degrees.  So ewres=1 means that your cell width is one 
>> degree.  Most other projections have a cell unit of meters.  For 
>> example an ewres=1 in an UTM projection would mean that your cell 
>> width is one meter.  To change your resolution, you can use
>>
>> g.region res=your_res
>>
>> for example
>>
>> g.region res=00:00:30 yields a 30 arc second resolution in a latlong 
>> projection.
>>
>> Hope this helps,
>> Ian
>>
>>
>> On Oct 10, 2005, at 7:35 AM, Bruno GUILLAUME wrote:
>>
>>> Dear GRASS users,
>>>
>>> My problem concerns a raster in lat-lon projection, having a given 
>>> resolution of ewres1,nsres1. For every cell, the category value is 
>>> expressed in kilogram.
>>> I need to transform it into  the same grid but with coarser 
>>> resolution, say ewres2=10*ewres1 and nsres2=10*nsres1, BUT the 
>>> transformation need to be mass-conservative (so, I need to get 
>>> exactly the same amount in kilograms with finer and coarser 
>>> resolution).
>>>
>>> Can I do in a simple way with GRASS ?
>>>
>>> Thanks in advance,
>>>
>>> Bruno Guillaume.
>>>
>>>
>> >
>> >
>> What happens if a big asteroid hits Earth? Judging from realistic 
>> simulations involving a sledge hammer and a common laboratory frog, 
>> we can assume it will be pretty bad.
>>  - Dave Barry
>>
>>
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>>
>
>
 >
 >
What happens if a big asteroid hits Earth? Judging from realistic 
simulations involving a sledge hammer and a common laboratory frog, we 
can assume it will be pretty bad.
  - Dave Barry


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