# identifying local maxima

3 messages
Open this post in threaded view
|

## identifying local maxima

 Dear R users, I have created a Loess surface in R, in which x is relative longitude by miles, y is relative latitude by miles, and z is population density at the neighborhood level. The purpose is to identify some population centers in the region. I'm wondering if there is a way to determine the coordinates (x,y) of each center, so I can know exactly where they are. Let me use the "elevation" data set in geoR to illustrate what have done: require(geoR) data(elevation) elev.df <- data.frame(x = 50 * elevation\$coords[,"x"], y = 50 * elevation\$coords[,"y"], z = 10 * elevation\$data) elev.loess <- loess(z ~ x * y, data = elev.df, degree = 2, span = 0.1) grid.x <- seq(10, 300, 1) grid.y <- seq(10, 300, 1) grid.mar <- list(x=grid.x, y=grid.y) elev.fit<-expand.grid(grid.mar) z.pred <- predict(elev.loess, newdata = elev.fit) persp(seq(10, 300, 5), seq(10, 300, 5), emp.pred, phi = 45, theta = 45, xlab = "X Coordinate (feet)", ylab = "Y Coordinate (feet)", main = "Surface elevation data") With this, what's the right way to determine the coordinates of the local maixma on the surface? Thanks. Gary         [[alternative HTML version deleted]] ______________________________________________ [hidden email] mailing list https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.