Hi R users,
I have been wandering around several manuals (sp, maptools, and
PBSmapping) to find out how to create polygons from points. Basically,
what I would like to do is to compute the area where two ellipses
overlap.
I can easily create the coordinates (x,y) of an ellipse.
library(CircStats)
library(sp)
library(PBSmapping)
# Draw a standard deviational ellipse
ElpCoords<-function(sigma_x,sigma_y,angle)
{
theta<-seq(0,2*pi,length=2000)
x<-cos(theta)
y<-sin(theta)
x1<-x*sigma_x
y1<-y*sigma_y
new_x<-x1*cos(rad(angle))-y1*sin(rad(angle))
new_y<-x1*sin(rad(angle))+y1*cos(rad(angle))
coords=cbind(new_x,new_y)
}
Using the function above, I created two ellipses;
el1<-ElpCoords(3,1.5,45)
el2<-ElpCoords(4,2.2,125)
Now I am stuck. How can I change these points forming ellipses into
polygons? I am believing that once I convert them into polygons I can
compute the overlapped area by using
el1Poly<-SpatialPolygons2PolySet(xxx_polygon_of_el1)
el2Poly<-SpatialPolygons2PolySet(xxx_polygon_of_el2)
overlappedArea<-joinPolys(el1Poly,eliPoly)
if(length(overlappedArea)>0)
{
combinedArea<-combinePolys(overlappedArea)
AreaSize<-calcArea(combinedArea)
}
else
{
warning('No overlapped area found')
}
So I would like to know processes to get to the last part.....
In addition, I have been wondering if there are tutorial books on
spatial stats/GIS on R. I am basically reading [R], [R-Geo], and R
News...
Thank you very much.
Takatsugu Kobayashi
PhD student
Indiana University Bloomignton
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