# Finds points in a polygon Given a polygon and a set of points this function returns the subset of points that are within the polygon. ```r pointsInPoly(poly, points, ...) ``` ## Arguments - `poly`: an $nx2$ matrix of polygon vertices. Matrix columns correspond to vertices' x and y coordinates, respectively. - `points`: an $mx2$ matrix of points. Matrix columns correspond to points' x and y coordinates, respectively. - `...`: currently no additional arguments. ## Returns If points are found with the polygon, then a vector is returned with elements corresponding to the row indices of `points`, otherwise `NA` is returned. ## Details It is assumed that the polygon is to be closed by joining the last vertex to the first vertex. ## Author(s) Andrew O. Finley finleya@msu.edu , Sudipto Banerjee sudiptob@biostat.umn.edu , ## Examples ```r ## Not run: ##Example 1 points <- cbind(runif(1000, 0, 10),runif(1000, 0, 10)) poly <- cbind(c(1:9,8:1), c(1,2*(5:3),2,-1,17,9,8,2:9)) point.indx <- pointsInPoly(poly, points) plot(points, pch=19, cex=0.5, xlab="x", ylab="y", col="red") points(points[point.indx,], pch=19, cex=0.5, col="blue") polygon(poly) ##Example 2 ##a function to partition the domain tiles <- function(points, x.cnt, y.cnt, tol = 1.0e-10){ x.min <- min(points[,1])-tol x.max <- max(points[,1])+tol y.min <- min(points[,2])-tol y.max <- max(points[,2])+tol x.cnt <- x.cnt+1 y.cnt <- y.cnt+1 x <- seq(x.min, x.max, length.out=x.cnt) y <- seq(y.min, y.max, length.out=y.cnt) tile.list <- vector("list", (length(y)-1)*(length(x)-1)) l <- 1 for(i in 1:(length(y)-1)){ for(j in 1:(length(x)-1)){ tile.list[[l]] <- rbind(c(x[j], y[i]), c(x[j+1], y[i]), c(x[j+1], y[i+1]), c(x[j], y[i+1])) l <- l+1 } } tile.list } n <- 1000 points <- cbind(runif(n, 0, 10), runif(n, 0, 10)) grd <- tiles(points, x.cnt=10, y.cnt=10) plot(points, pch=19, cex=0.5, xlab="x", ylab="y") sum.points <- 0 for(i in 1:length(grd)){ polygon(grd[[i]], border="red") point.indx <- pointsInPoly(grd[[i]], points) if(!is.na(point.indx[1])){ sum.points <- length(point.indx)+sum.points text(mean(grd[[i]][,1]), mean(grd[[i]][,2]), length(point.indx), col="red") } } sum.points ## End(Not run) ```

pointsInPoly function