Hi there,

How about join.asc at adehabitat packages?
I have done this kind of points-raster overlap without problem using that
funcion.

Cheers

milton

On Fri, Jun 5, 2009 at 2:49 PM, Kamran Safi <ksafi@orn.mpg.de> wrote:

> Hi,
>
> I am not sure this is trivial. I think the simplest solution would be to
> find the closest grid cell centre (maybe using spDistN1 or simple vector
> length) and get the closest grid cell with environmental data and assign it
> to your animals' position. You can further complicate things by not taking
> simply the next closest point, but calculate the weighted mean (using the
> inverse of distance of the cell centres to the animals' location as weighing
> variable) or maybe most elegantly use kriging (or linear models), and
> extrapolate the value for the location. This is a classical geographers'
> problem of interpolation and not simply done by overlay(), which probably
> mimics the first solution of getting the next best grid cell (I am also not
> entirely sure whether overlay works with spatialPoints and spatialPixels).
> Weighted mean maybe a straightforward solution.
>
> Hope this helps,
>
> Kami
>
>
> Struve, Juliane wrote:
>
>> Dear list,
>>
>> I am trying to incoporate spatial information (for example distance) into
>> a movement model by reading an ascii -b converted raster and matching the
>> raster with points of a movement path (for example
>> fishmove$coord[fishmove$day==1]. Below is a section of my code to explain
>> the problem. This code does not work because the coordinates of the movement
>> path are not the same as those in the raster. Rounding the coordinates does
>> not seem to solve the problem. Maybe the closest point would have to be
>> found, but i am not sure how to approach this.  Is there another perhaps
>> easier way ?
>>
>> Dist_DF=data.frame(readAsciiGrid("distance.txt"))
>> Dist_shoreDF$coord = paste(round(Dist_DF$s1),round(Dist_DF$s2),sep=",")
>> names(Dist_DF)[1]="Dist"
>> Dist_DF$Dist[Dist_shoreDF$coord==fishmove$coord[fishmove$day==1]]
>>
>> I would be grateful for any help.
>>
>> Many thanks,
>>
>> Juliane
>>
>>
>>
>>
>>
>>
>>
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>>
>
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