Prevent minor discrepancy in pixel resolution using Spatstat
When I specify eps=25 (m resolution) in a call to distmap...
library(spatstat)
temp <- data.frame(x=-670049.2, y=752814.6, X2=-669961.9, Y2=752648.2)
subwin<-owin(xrange=c(-100, 100) + sort(c(temp$x, temp$X2)),
yrange=c(-100, 100) + sort(c(temp$y, temp$Y2)))
trajpsp<-psp(temp$x,temp$y, temp$X2, temp$Y2, subwin, check=TRUE)
plot(trajmap<-distmap(trajpsp, eps=25))
trajmap$xstep
[1] 23.94167
trajmap$ystep
[1] 24.42667 ...The resulting resolution is slightly different than 25x25 metres. So now when I use it as a mask:
trajmap$v<-ifelse(trajmap$v>50, 0, 1) library(maptools)
...and convert it to a RasterLayer for matrix algebra with another raster
trajrast<-raster(as.SpatialGridDataFrame.im(from=trajmap)) tempmap<-crop(habmap, extent(trajrast)) # tempmap.grd is attached top<-table(getValues(tempmap*trajrast))
Error in compare(c(e1, e2)) : Different bounding box Error in getValues(tempmap * trajrast) : error in evaluating the argument 'x' in selecting a method for function 'getValues' ...it doesn't work because the resolution is not exactly equal. Now I can sometimes trick it when the number of rows and cells are still equal, BUT... extent(trajrast)<-extent(tempmap)
top<-table(getValues(tempmap*trajrast))
Error in compare(c(e1, e2)) : nrows different Error in getValues(tempmap * trajrast) : error in evaluating the argument 'x' in selecting a method for function 'getValues' ...This is not always the case! How can I prevent the numbers of rows and columns from being so slightly different because of a minor different in resolution? Otherwise put, how can I make the actual resolution of my distmap image exactly 25m as desired? Tyler -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://stat.ethz.ch/pipermail/r-sig-geo/attachments/20100217/d87eca10/attachment.html> -------------- next part -------------- A non-text attachment was scrubbed... Name: tempmap.grd Type: application/octet-stream Size: 596 bytes Desc: not available URL: <https://stat.ethz.ch/pipermail/r-sig-geo/attachments/20100217/d87eca10/attachment.obj>