Dear Rolf,
Barry suggestion addressed my question and the function lookup.img as well.
Thanks
Jose

On Mon, Jul 23, 2012 at 5:29 PM, Rolf Turner <r.turner@auckland.ac.nz>wrote:

> On 24/07/12 01:26, Jose Funes wrote:
>
>> Dear list,
>> I have point pattern data and would like to attach/add covariates as
>> raster
>> (image or grid) to it. For example as the case of the bei data with
>> bei.extra with covariates.
>>
>
> I'm afraid I don't understand what it is that you need to do.
> What do you mean by "attach/add"?  In the example of the
> "bei" data that you refer to, the images (covariates) "elev"
> and "grad" are components of the list "bei.extra" which is
> a separate object from the point pattern "bei".  The object
> "bei.extra" is not "attached" to the object "bei" in any way.
>
> Barry Rowlingson suggested that you might want to find the
> values of a covariate associated with each point of a point
> pattern.   The easiest way to do this is to use the (undocumented)
> function "lookup.im()".
>
> E.g.:
>
>     em <- with(bei.extra,lookup.im(elev,**bei$x,bei$y))
>     gm <- with(bei.extra,lookup.im(grad,**bei$x,bei$y))
>
> Then you could "attach" these values to the point pattern as
> *marks*:
>
>     marks(bei) <- data.frame(elev=em,grad=gm)
>
> Is this (anything like) what you want to do?
>
>     cheers,
>
>         Rolf Turner
>
> P. S.  Adrian:  Do you think we should make "lookup.im()" into a
> *documented*
> function?  I have found myself recommending its use to inquirers on more
> than
> one occasion.
>
>         R.
>

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