[R-sig-Geo] creating irregularly-shaped grids for kriging

[Mauricio Zambrano]

Hi Craig,

If you have a shapefile of your agricultural fields, you can use the
function "readShapePoly" (maptools package) for getting the polygons
of your agricultural fields, and then use the "spsample" command to
create the grid within the polygons, as Paul mentioned. Finally, you
can use the grid generated by spsample as the object with prediction
locations.

Something like:

1) require(maptools)

2) shp <- readShapePoly(yourshapefilename, proj4string=yourp4s)

3) agr.grid <- spsample(shp, type="regular", cellsize=yourcell.size,
offset = c(0.5, 0.5))

4) gridded(agr.grid) <- TRUE

5) x <- krige(yourvalue~1, locations=yourlocations, newdata=agr.grid,
model=yourmodel) (or the autoKrige version of this)


I hope this helps.

Kinds,

Mauricio

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> Hi Craig,
>
> The easiest way is to get a polygon of you study area and than use
> spsample() to create a grid. You could also make a convex hull using the
> chull command and spsample from that. Depending on your configuration of
> points this might be an option. You could try autoKrige from the automap
> pacakge to get an idea of how this last option looks, it uses a convex hull
> to create a new_data object if it is not given.
>
> library(automap)
> data(meuse)
> coordinates(meuse) = ~x+y
>
> kr = autoKrige(meuse)
> plot(kr)
>
> cheers,
> Paul
>
> Scanlan, Craig wrote:
>>
>> Hi all,
>>  I need to krige data that is irregularly spaced within irregularly
>> shaped areas (agricultural fields).    At present, I am creating a regular
>> grid for newdata in
>> krige(data,newdata....) by
>>  x.range <- as.integer(range(a2 at coords[,1]))
>> y.range <- as.integer(range(a2 at coords[,2]))
>> grd <- expand.grid(x=seq(from=x.range[1], to=x.range[2], by=10),
>> y=seq(from=y.range[1], to=y.range[2], by=10) )
>>
>> I have not been able to find a method to trim the newdata grid to the
>> same shape as the original data - is this possible?
>>  The task I am trying to achieve is the same as creating meuse.grid from
>> meuse data.
>>  Can anyone help?
>>  Regards,
>>  Craig.
>>
>>
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>
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