[R-sig-Geo] spliting lines on equal-space points.

[Roger Bivand]

On Thu, 2 Oct 2008, milton ruser wrote:

> Dear all,
> I have a shapefile with line features (like for example drainage),
> and I need to generate another shape with points using
> the features from the first shape.
>
> But the points is not the points that I can get from the lines.
> I need, for example, define that I want one point each 50 meters,
> and the points have ~ 50 meters of space between other points
> if we follow the "flow" of drainage.
>
> I wrote this simple code to try short the time for helpers.
>
> library(maptools)
>
> xx <- readShapeLines(system.file("shapes/fylk-val.shp",
> package="maptools")[1],
>    proj4string=CRS("+proj=utm +zone=33 +datum=WGS84"))
> plot(xx, col="blue", axes=T)
>
> xx.selectone<-xx[xx$VALINJE_==20,]
>
> plot(xx.selectone, col="red", add=T)

spsample(xx.selectone, n=82, type="regular")

gets you there directly - choose n either directly (here roughly one 
sample per km) or based on the object length:

sum(sapply(slot(xx.selectone, "lines"), function(x) sapply(slot(x,
   "Lines"), LineLength)))

Also see the spsurvey package for an industry-strength development of 
sampling in stream networks.

Roger

>
> Best wishes,
>
> miltinho astronauta
> brazil
>
> 	[[alternative HTML version deleted]]
>
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no