[R-sig-Geo] doubts with density ppp function

[Rolf Turner]

On 09/10/12 23:16, Julia Chacon Labella wrote:
> Just a short and simple question,
>
> How can I extract the values of an image created with "density.ppp"
> function?

     See ?"[.im".

     Let your image be called "A".

     If you have coordinates x and y at which you wish to extract the
     image values you can use:

         A[i=data.frame(x=x,y=y)]

     If you have pairs of indices (of pixels) at which you want to extract
     the image values you can form an n x 2 matrix (say "M") each row
     of which is an index pair and use

         A[i=M]
>
> And...there is any way to rotate this images? I tried with rotate() but I
> guess this is only for the ppp object, not for an image.
>

     You can use the affine.im() method for affine().  Or write a wrapper,
     rotate.im() for affine.im(), something like:

     rotate.im <- function(X,theta=pi/2) {
         co <- cos(theta)
         si <- sin(theta)
         m <- matrix(c(co,si,,-si,co),2,2)
         affine(X,mat=m)
     }

HTH

     cheers,

         Rolf Turner