Changing the coordinates of a SpatialGridDataFrame

Hi there,

I have a SpatialGridDataFrame object and I wish to round the coordinates associated with the grid to three decimal places in order to match points in this object with points on another spatial object where the coordinates are recorded to three decimal places.

Some information about the obj. It is quite a large grid that covers Australia with over 2 million points in it.

coords1<- coordinates(obj)
dim(coords1)

[1] 2287841       2

head(coords1)

             x         y
[1,] 112.0013 -9.999004
[2,] 112.0263 -9.999004
[3,] 112.0513 -9.999004
[4,] 112.0763 -9.999004
[5,] 112.1013 -9.999004
[6,] 112.1263 -9.999004

obj at coords

             x          y
[1,] 112.0013 -43.999004
[2,] 154.0013  -9.999004

bbox(obj)

        min        max
x 111.9888 154.013789
y -44.0115  -9.986504
My first attempt to do the rounding was based on the coordinates function. When I read the help file it  indicates that one can set the coordinates by passing a matrix here. I get an error as listed below.

## First suggestion
coordinates(obj)<- round(coordinates(obj),3)

Error in `coordinates<-`(`*tmp*`, value = c(112.001, 112.026, 112.051,  :
   setting coordinates cannot be done on Spatial objects, where they have already been set

A second way was suggested to me that involved rounding obj at coords directly. This produces no errors but also doesn't do the job as you can see below. It does round the obj at coords part but this doesn't have any effect on coordinates(obj) or on bbox(obj).

## Second suggestion
roundcoordinates = function(obj, r = 3) {

+   obj at coords = round(obj at coords, r)
+   obj
+ }

obj<- roundcoordinates(obj)

obj at coords

            x       y
[1,] 112.001 -43.999
[2,] 154.001  -9.999

bbox(obj)

        min        max
x 111.9888 154.013789
y -44.0115  -9.986504

coords2<- coordinates(obj)
head(coords2)

             x         y
[1,] 112.0013 -9.999004
[2,] 112.0263 -9.999004
[3,] 112.0513 -9.999004
[4,] 112.0763 -9.999004
[5,] 112.1013 -9.999004
[6,] 112.1263 -9.999004
Does anyone know how to go about this in a way that will also not cause other potential problems - ie changing obj at coords doesn't automatically update coordinates(obj) or bbox(obj).

Thanks in advance,

David

Dr David Clifford
Research Scientist
CSIRO Division of Mathematics, Informatics and Statistics
Phone: +61 7 3214 2816 | Fax: +61 7 3214 2855
David.Clifford at csiro.au | www.csiro.au | www.csiro.au/people/David.Clifford.html
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