The R Book

The spatstat library

You need to use the function ppp to convert your coordinate data into an object of class ppp representing a point pattern data set in the two-dimensional plane. Our next dataframe contains information on the locations and sizes of 3359 ragwort plants in a 30 m x 15 mmap:

data<-read.table("c:\\temp\\ragwortmap2006.txt",header=T)
attach(data)
names(data)

 [1] "ROW"           "COLUMN"  "X"         "Y"       "rosette"
 [6] "regenerating"  "stems"   "diameter"  "xcoord"  "ycoord"
[11] "type"

The plants are classified as belonging to one of four types: skeletons are dead stems of plants that flowered the year before, regrowth are skeletons that have live shoots at the base), seedlings are small plants (a few weeks old) and rosettes are larger plants (one or more years old) destined to flower this year. The function ppp requires separate vectors for the x and y coordinates: these are in our file under the names xcoord and ycoord. The third and fourth arguments to ppp are the boundary coordinates for x and y respectively (in this example c(0,3000) for x and c(0,1500) for y). The final argument to ppp contains a vector of what are known as ‘marks’: these are the factor levels associated with each of the points (in this case, type is either skeleton, regrowth, seedling or rosette). You give a name to the ppp object (ragwort) and define it like this:

ragwort<-ppp(xcoord,ycoord,c(0,3000),c(0,1500),marks=type)

You can now use the object called ragwort in a host of different functions for plotting ...