Sample transects — sample_transects • TrailMapper

Sample transects.

sample_transects(x, y, interval, keep = 1, spar = 0.3,
                 rm.intersections = TRUE, transect.length = NULL)

Arguments

x: A SpatRaster containing at least one layer.
y: A SpatVector containing a polygon or a line that defines the boundary of an area.
interval: (Numeric). Distance between transects.
keep: (Numeric). The proportion of vertices from the polygon to be retained. Default value is 1.
spar: (Numeric). The smoothing factor of the centerline ranging from 0 to 1. The higher the value, the greater the smoothing. Default value is 0.3.
rm.intersections: (Logical). Should overlapping transects be removed? Default is TRUE.
transect.length: (Numeric). Transect length. By default, this is automatically estimated.

Value

The result is a list consisting of three objects:

The centerline of the polygon as SpatVector.
The data frame containing the cell values for the center points.
The data frame containing cell values for the transects.

Examples

library("terra")
#> terra 1.9.27

DEM = system.file("DEM.tif", package = "TrailMapper")
DEM = rast(DEM)

boundary = system.file("boundary.gpkg", package = "TrailMapper")
boundary = vect(boundary)
boundary$ID = 1 # this is now required to work

output = sample_transects(DEM, boundary, interval = 2)
str(output)
#> List of 3
#>  $ centerline    :S4 class 'SpatVector' [package "terra"]
#>  $ central_points:'data.frame':	9 obs. of  4 variables:
#>   ..$ ID : num [1:9] 1 2 3 4 5 6 7 8 9
#>   ..$ DEM: num [1:9] 111 111 110 110 110 ...
#>   ..$ x  : num [1:9] 631877 631876 631876 631875 631874 ...
#>   ..$ y  : num [1:9] 5814235 5814233 5814231 5814229 5814227 ...
#>  $ transects     :'data.frame':	251 obs. of  4 variables:
#>   ..$ ID : int [1:251] 1 1 1 1 1 1 1 1 1 1 ...
#>   ..$ x  : num [1:251] 631877 631877 631877 631877 631877 ...
#>   ..$ y  : num [1:251] 5814235 5814235 5814235 5814235 5814235 ...
#>   ..$ DEM: num [1:251] 111 111 111 111 111 ...

# plot centerline
plot(output[[1]], main = "Centerline")

# plot central points
points(output[[2]]$x, output[[2]]$y, pch = 19)

# plot transects points
for (i in unique(output[[3]]$ID)) {
  d = output[[3]][output[[3]]$ID == i, ]
  lines(d$x, d$y, lwd = 2)
}