[GRASS-user] Converting slopes from huge DEM into vector (area)

[Rainer M. Krug]

Hi Hamish

thanks a lot for your information - I'll try it out and come back if I 
have further problems

Rainer


Hamish wrote:
> Rainer M. Krug wrote:
>> I have a huge raster, representing the slopes of a huge DEM (Rows: 
>>    25960, Columns: 23211, Total Cells:  602557560, Type CELL).
>> I would like to use R.to.vect to convert it to a vector layer of type 
>> area. Due to memory requirements, it does not work in one step.
>>
>> I thought of splitting the raster into several smaller rasters (let's 
>> say into 100 smaller rasters of the same resolution) for which I could
> 
> you probably only need to split it into 4 parts, not 100.
> 
> 
>> use r.to.vect to create the vector layers and in a final step patch
>> the  vector layers together again.
>>
>> Before going into the details: is this a feasible approach (I can't 
>> reduce the resolution as the resolution is needed)
> 
> sure. use v.patch to recombine the parts, but mind the attributes carry
> through.
> 
>> or is there another solution?
> 
> probably several
>  
>> But I am stuck in the first step:
>> how can I split one large raster layer into several smaller?
> 
> actually you don't need to, just change the region with g.region.
> Raster ops only happen in the current region. set the north/south
> bounds to a quarter of the map's height and then r.to.vect will
> only work on that part of it. Vector ops (for the most part) ignore
> the current region settings.
>  
>> and:
>> What is the easiest way to write the script to do the calculations for
>> all 100 raster layers? (I haven't used the scripting in GRASS 6.2.1
>> yet,  but I have done a bit scripting under the bash shell)
> 
> for MAP in `g.mlist type=rast pattern=*` ; do
>    echo "[$MAP]"
>    g.region rast=$MAP
>    r.to.vect $MAP ....
> done
> 
> 
> 
> Hamish


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