On 19/07/16 01:16, Adrienne Wootten wrote:
All,
Greetings! I hope things are going well for all! I apologize if someone's
already answered this and I'm just not finding it. Here's what I'd like to
do, but I'm hitting a brick wall with it.
I have two sets of points for which I've already determined which ones
points for the boundaries with the chull function. What I need for what
I'm doing is the coordinates where the two resulting polygons overlap.
These are not raster grids, nor shapefiles. What I have to work with are
the two data frames with the points at the vertices of each polygon
(included below).
chx1
x y
1 0.5822569 -0.5555878
2 0.5338428 -0.5883604
3 -0.3442943 -0.6701115
4 -0.7409293 0.2286962
5 0.2147221 0.8061485
6 0.4914146 0.4941865
7 0.5822569 -0.5555878
chx2
x y
1 0.7163506 -0.4357497
2 0.6513128 -0.5395180
3 0.1818315 -0.6317423
4 -0.6394281 -0.5765610
5 -0.6044681 0.1831627
6 -0.5799485 0.3231473
7 0.2248476 0.9601908
8 0.7163506 -0.4357497
If anyone has any ideas on how to get what I'm after I'd appreciate it!
I've tried a lot of things from the raster, rgeos, and more. Knowing me
it's something obvious I'm just not seeing right now.
You can do this very easily using the spatstat package:
library(spatstat)
X1 <- read.table(textConnection("
x y
1 0.5822569 -0.5555878
2 0.5338428 -0.5883604
3 -0.3442943 -0.6701115
4 -0.7409293 0.2286962
5 0.2147221 0.8061485
6 0.4914146 0.4941865
7 0.5822569 -0.5555878"))
X2 <- read.table(textConnection("
x y
1 0.7163506 -0.4357497
2 0.6513128 -0.5395180
3 0.1818315 -0.6317423
4 -0.6394281 -0.5765610
5 -0.6044681 0.1831627
6 -0.5799485 0.3231473
7 0.2248476 0.9601908
8 0.7163506 -0.4357497"))
X1 <- reverse.xypolygon(X1) # Vertices are in the wrong
X2 <- reverse.xypolygon(X2) # (clockwise) order.
W1 <- owin(poly=X1)
W2 <- owin(poly=X2)
WI <- intersect.owin(W1,W2)
plot(union.owin(W1,W2),col="blue",main="")
plot(WI,add=TRUE,col="red")
HTH
cheers,
Rolf Turner
P.S. To extract the coordinates of the intersection polygon you can do:
WI$bdry[[1]]
R. T.
--
Technical Editor ANZJS
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276
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