[R-sig-Geo] Drawing lines in raster cells

[Lionel]

Hi Oscar,

Thanks for your help, what I would like to get is something similar to this:
http://www.google.fr/imgres?q=species+range+shift&start=280&um=1&sa=N&hl=fr&biw=1366&bih=647&tbm=isch&tbnid=MdhZVMKVLMSH3M:&imgrefurl=http://www.scielo.sa.cr/scielo.php%3Fscript%3Dsci_arttext%26pid%3DS0034-77442008000200028&docid=9u3QDKVd0hdQqM&imgurl=http://www.scielo.sa.cr/img/revistas/rbt/v56n2/art28i2.jpg&w=363&h=432&ei=cbiPUe_4BqO80QX-hoCIBw&zoom=1&iact=hc&vpx=588&vpy=170&dur=342&hovh=180&hovw=152&tx=83&ty=124&page=10&tbnh=159&tbnw=134&ndsp=30&ved=1t:429,r:84,s:200,i:256

Where each raster cells with a certain values (say 1) get crossed by a 
diagonal line.

Your code is achieving something different, concerning the object 
created the best would be a Spatial* object, however I think I could be 
able to find a way around using ggmap.

Thanks again,
Lionel

On 12/05/2013 16:23, Oscar Perpiñán Lamigueiro wrote:
> Hi Lionel,
>
> With this code you will draw lines connecting raster cells with a
> certain value. I am not sure if you also need to build a SpatialLines
> object with them (which you won't get with my code):
>
> library(raster)
> library(latticeExtra) ## to use +.trellis and layer()
>
> r1<-raster(ncols=10,nrows=10)
> r1[]<-sample(0:1,100,replace=TRUE)
>
> ## extract coordinates of those cells with a condition
> myCells <- Which(r1==1, cells=TRUE)
> xy <- xyFromCell(r1, myCells)
>
> ## border and border.lwd are only needed to highlight the cells boundaries
> spplot(r1, at=c(0, 0.5, 1), border='black', border.lwd=0.3) +
>      layer(llines(xy, type='b', col='black'))
>
>
> Best,
>
> Oscar.
>
> Lionel <s6lihert at uni-bonn.de> writes:
>
>> Dear List,
>>
>> I would like to draw lines in raster cells with a certain values, I can
>> work around this with a for loop but as always this solution only works
>> for small datasets (which is not my case), I would therefore like to
>> have your opinion on this;
>>
>> #the code
>> library(maptools) #to use spRbind
>> out<-NULL
>> r1<-raster(ncols=10,nrows=10)
>> r1[]<-sample(0:1,100,replace=TRUE)
>> for(i in 1:ncell(r1)){
>>     if(r1[i]==1){
>> lines<-SpatialLines(list(Lines(list(Line(matrix(c(xyFromCell(r1,i)+(res(r1)/2),xyFromCell(r1,i)-(res(r1)/2)),ncol=2,byrow=TRUE))),ID=as.character(i))))
>>       if(is.null(out)){
>>         out<-lines }
>>          else {out<-spRbind(out,lines)}
>>       }
>>     print(i)
>> }
>>
>> Thank you in advance,
>
>