Analysing spatial point patterns in R - CSIRO

9.3 Example 59
You may also notice a line of trees at the right-hand edge of the study region. It looks
as though the study region may have included some trees that were planted as a boundary or
avenue. This sticks out like a sore thumb if we plot the x coordinates of the trees:
> hist(nztrees$x, nclass = 25)
Histogram of nztrees$x
Frequency
0 2 4 6 8 10
0 50 100 150
We might want to exclude the right-hand boundary from the study region, to focus on the
pattern of the remaining trees. Let’s say we decide to trim a 5-foot margin off the right-hand
side.
First we create the new, trimmed study region:
> chopped win chopped chopped
window: rectangle = [0, 148] x [0, 95] feet
(Notice that chopped is not a point pattern, but simply a rectangle in the plane.)
Then, using the subset operator [.ppp, we simply extract the subset of the original point
pattern that lies inside the new window:
> nzchop summary(nzchop)
Planar point pattern: 78 points
Average intensity 0.00555 points per square foot
Window: rectangle = [0, 148]x[0, 95]feet
Window area = 14060 square feet
Unit of length: 1 foot
> plot(density(nzchop, 10))
> plot(nzchop, add = TRUE)
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