从R中的空间点计算角度

Question

I am looking at some dispersal data and would like to get distance between points and also the angle between those points. So far, I have only been able to achieve the first part. Using the teal data from the adehabitatLT package I have done this:

require("adehabitatLT")
require("sp")
data("teal")
teal <- teal[1:10 ,]
capsd <- SpatialPointsDataFrame(coords = SpatialPoints(coords = 
    teal[, c("x","y")], proj4string = CRS("+proj=longlat +datum=WGS84 
    +ellps=WGS84 +towgs84=0,0,0")), data=teal)
capdistance <- as.data.frame(pointDistance(capsd))

The capdistance is a 10x10 dataframe displaying the distances between the first 10 points of the teal dataset.

Does anyone know how I would calculate the angle between these points to create a similar matrix to the capdistance data.frame? I have searched, but so far I have not found anything that would calculate the angle between two set locations. Any help would be greatly appreciated.

EDIT

So I have been looking around and it would seem that the bearing function from the geosphere package would be useful for this, but I am still (at least) a step away from working this all the way through:

require("geosphere")
capbearing1 <- bearing(capsd[1:10 ,], capsd[1 ,])
capbearing2 <- bearing(capsd[1:10 ,], capsd[2 ,])

I could repeat this ten times to achieve ten lists each one giving the angle of one of the ten points relative to all ten points (itself and the nine others); however, I would really like this to operate smoothly to give all ten lists at once as a single matrix; again, any help is very appreciated.

cygps gave some good code if you are utilizing UTMs in a single zone and have limited data points, so try that out if you have those parameters.

Answer 1

foo <- function(df) {
      x1 <- x2 <- df$x
      y1 <- y2 <- df$y
      Xpair<-merge(x1,x2)
        names(Xpair)<-c("x1","x2")
      Ypair<-merge(y1,y2)
       names(Ypair)<-c("y1","y2")

      dist <- c(sqrt((Xpair$x1 - Xpair$x2)^2 + (Ypair$y1 - Ypair$y2)^2), NA)

      dx <- c(Xpair$x1 - Xpair$x2, NA)
      dy <- c(Ypair$y1 - Ypair$y2, NA)
      abs.angle <- ifelse(dist < 1e-07, NA, atan2(dy, dx))
      so <- list(dist,  abs.angle)
      return(so)
    }

I adapted this function from adehabitatLT:as.ltraj . It produces your distance and absolute angle matrices (assuming you wanted distances and angles between all points, not time-ordered distances and angles).