[STATSGRASS] "Neighbourhood modifier" from r.mapcalc in R?

[Rainer M Krug]

Thanks - I'll look into your suggestions later this week.

Rainer

Roger Bivand wrote:
> On Tue, 16 Oct 2007, Rainer M Krug wrote:
> 
>> Hi
>>
>> I want to do some map calculations which involve binominal distributed 
>> random numbers which I can not obtain in r.mapcalc. Therefore I import 
>> the raster via readRAST6() into R and I want to do the calculations 
>> there. But I am stuck...
>>
>> In r.mapcalc I use somthing like
>>
>> OUTPUT=INPUT1[-2,-2]*INPUT2+INPUT1[+2,+2]*INPUT2
>>
>> How can I translate this into R?
>>
>> rA <- readRAST6("INPUT1")
>> rB <- readRAST6("INPUT2")
>> but now?
>>
>> rA$A gives me all cell values,
>> rA[1:2,1:2]$A gives me the cell values from columns and row 1 and 2,
>>
>> But I have no idea where I should put the offset in.
> 
> As designed, the SpatialGridDataFrame objects are intended to have the 
> same regions in the g.region sense. They do have grid slots, and you 
> could shift the whole grid by changing the cellcentre.offset slot in the 
> GridTopology object in the grid slot, and update the bbox. This would 
> give grids that are offset in relation to each other, but to get the 
> values across all offset grids, you'd need to back the original 
> SpatialGrid out to SpatialPoints, and use the overlay() method for 
> SpatialPoints and SpatialGridDataFrame objects.
> 
> An alternative that would need coding is to look inside the "[" method 
> for SpatialGridDataFrame objects (which you refer to above) and see how 
> one might write a relative reference function which would not subset on 
> the i and j arguments, but shift by row and column.
> 
> Probably the first alternative involves less work.
> 
> Roger
> 
>>
>> Rainer
>>
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>