fixedPoint: Orientation, Position and Length of the Experimental Unit

Description

Generates a number of equidistant spatial points in an area. Fixed a couple of points in the image and the number of segments included, the function determines the position of the segments according to the length of the segment. The function relates the real dimension of the segment measurement to the image dimension. The function is useful for sizing plot sizes in the field, it also facilitates the generation of experimental units in the field.

Usage

fixedPoint(start, end, npoints, long)

Value

xy: Data vector with the coordinate of the points

Arguments

start: Starting point
end: Point at the end
npoints: Number of points
long: Segment length

Details

This function is used by imageField.

Examples

Run this code

library(rPAex)
prg1 <- system.file("examples/Ex-01.R", package="rPAex")
source(prg1)
r<-data1()
oldpar<-par(mar=c(2,2,4,2),cex=0.8)
raster::image(r,col=col2rgb(10),main="Orientation, position and length of the experimental unit")
# P<-locator(2)
P<-list(x=c(20,80),y=c(40,80))
P<-cbind(x=P$x,y=P$y)
Q<-fixedPoint(start = P[1,],end = P[2,],4,long = 10)
x <- Q[,1]; y <- Q[,2]
s <- seq(length(x)-1)  # one shorter than data
segments(x[s], y[s], x[s+1], y[s+1], col= c(1,0),lwd=2)
text(Q,cex=1.5)
text(20,80,"Total length   = 72.11 units")
text(20,70,"total segments = 4")
text(60,40,"   Free space  = 10.7037 units")
text(60,30,"Segment length = 10 units")
text(50,10,"fixedPoint(start ,end ,npoints = 4,long = 10)")
text(20,35,"start",cex=1.5)
text(80,75,"end",cex=1.5)
par(oldpar)