The following might work and could definitely be improved for speed  
and error catching.


require(sp)
require(maptools)

slopes <- function(k){
	x <- k[[1]]
	y <- vector(length=nrow(x)-1)
	for (i in 1: nrow(x)-1){
		y[i] <-(x[i+1,2]-x[i,2])/(x[i+1,1]-x[i,1])
		}
		return(y)
	}
	
angles <- function(k){
	y <- vector(length=length(k)-1)
	for (i in 1: length(k)-1){
		y[i] <- atan((k[i+1]-k[i])/(1+k[i]*k[i+1]))
		}
		return(y)
	}

xx <- readShapeLines(system.file("shapes/fylk-val.shp",  
package="maptools")[1],
  proj4string=CRS("+proj=utm +zone=33 +datum=WGS84"))

a <- coordinates(xx)
sl <- lapply(a, slopes)
ag <- lapply(sl, angles)


Nikhil Kaza
Asst. Professor,
City and Regional Planning
University of North Carolina

nikhil.list@gmail.com

On Jul 30, 2010, at 3:33 AM, Rainer M Krug wrote:

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>
> Hi
>
> a friend of mine wants (needs?) to determine the angle between  
> segments
> in an ESRI polyline (line vector feature). As there does not seem to  
> be
> an easy way in ArcGIS 9.2, I thought about askeng here:
>
> Is there way of calculating these angles between the different line
> segments in R (after importing the line feature into R)?
>
> Thanks,
>
> Rainer
>
> - --
> Rainer M. Krug, PhD (Conservation Ecology, SUN), MSc (Conservation
> Biology, UCT), Dipl. Phys. (Germany)
>
> Centre of Excellence for Invasion Biology
> Natural Sciences Building
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> Stellenbosch University
> Main Campus, Merriman Avenue
> Stellenbosch
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>
> Tel:        +33 - (0)9 53 10 27 44
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> Fax (FR):   +33 - (0)9 58 10 27 44
> email:      Rainer@krugs.de
>
> Skype:      RMkrug
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