Systematic or random point sample of line(s)

Creates a systematic or random point sample of an sp SpatialLinesDataFrame object based on distance spacing, fixed size or proportional size

The sdist argument will produce an evenly spaced sample, whereas n produces a fixed sized sample. The p (proportional) argument calculates the percent of the line-length. The LID column in the @data slot corresponds to the row.names of the SpatialLinesDataFrame object.

sample.line(
  x,
  d = 100,
  p = NULL,
  n = NULL,
  type = "regular",
  longlat = FALSE,
  min.samp = 1,
  ...
)

Arguments

x	sp class SpatialLinesDataFrame object
d	Sample distance. For regular sample.
p	Proportional sample size (length * p), expected value is 0-1. For regular or random.
n	Fixed sample size. For regular or random
type	Defines sample type. Options are "regular" or "random". A regular sample results in a systematic, evenly spaced sample.
longlat	TRUE/FALSE is data in geographic units, if TRUE distance is in kilometers
min.samp	Minimal number of sample points for a given line (default is 1 point)
...	Additional argument passed to spsample

Value

sp SpatialPointsDataFrame object.

Author

Jeffrey S. Evans <jeffrey_evans@tnc.org>

Examples

 require(sp)
 sp.lines <- SpatialLines(list(Lines(list(Line(cbind(c(1,2,3),c(3,2,2)))), 
               ID="2")))
 sp.lines <- SpatialLinesDataFrame( sp.lines, data.frame(ID=1:2, 
                                    row.names=c(1,2)) )

opar <- par(no.readonly=TRUE)
par(mfrow=c(2,2))
 # Create systematic sample at 20 km spacing 
 reg.sample <- sample.line(sp.lines, d = 20, type = "regular", 
                           longlat = TRUE)
   plot(sp.lines)
     plot(reg.sample, pch = 20, add = TRUE)
  box()
  title("systematic d = 20")

 # Create fixed size (n = 20) systematic sample
 reg.sample <- sample.line(sp.lines, n = 20, type = "regular", 
                           longlat = TRUE)  
   plot(sp.lines)
     plot(reg.sample, pch = 20, add = TRUE)
     box()
  title("systematic n = 20")
  
 # Create fixed size (n = 20) random sample 
 rand.sample <- sample.line(sp.lines, n = 20, type = "random", 
                            longlat = TRUE)  
   plot(sp.lines)
     plot(rand.sample, pch = 20, add = TRUE)
     box()    
     title("rand n = 20")
  
 # Create proportional (p = 0.10) random sample
 rand.sample <- sample.line(sp.lines, p = 0.10, type = "random", 
                            longlat = TRUE)  
   plot(sp.lines)
     plot(rand.sample, pch = 20, add = TRUE)
     box()
  title("rand p = 0.10")
par(opar)