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Smooth the geometry of a vector

Source: R/smoothGeom.r
smoothGeom.Rd

smoothGeom() makes line segments of a vector appear less angular.

Usage

# S4 method for class 'GVector'
smoothGeom(x, method = "Hermite", dist = NULL, angle = 3)

Arguments

x

A GVector.

method

Character: Method used to smooth line segments. Partial matching is used, and case does not matter:

  • "Hermite": Hermite interpolation (default): Guarantees that the output vector always passes through the original points. This method adds points (possibly many) by constructing cubic splines with points approximately dist apart. The number of points can be reduced by specifying a smaller value of angle, which specifies the minimum angle between two successive line segments.

  • "Chaiken": Chaiken's algorithm: Guarantees that the new vector always touches the midpoint of each original line segment. The points on the new line are at least dist apart.

dist

Numeric > 0 of NULL (default): Minimum distance (see method). Units are in map units. If NULL, then 2% of the minimum of the x-, y-, and z-extent will be used.

angle

Numeric > 0: Maximum angle for the Hermite algorithm. Default is 3.

Value

A GVector.

See also

simplifyGeom(), terra::simplifyGeom(), geometry cleaning, GRASS manual page for tool v.generalize (see grassHelp("v.generalize"))

Examples

if (grassStarted()) {

# Setup
library(sf)
library(terra)

# Example data
madRivers <- fastData("madRivers")
rivers <- fast(madRivers)
soam <- rivers[rivers$NAM == "SOAMIANINA"] # select one river for illustration

### Simplify geometry (remove nodes)

vr <- simplifyGeom(soam, tolerance = 2000)
dp <- simplifyGeom(soam, tolerance = 2000, method = "dp")
dpr <- simplifyGeom(soam, tolerance = 2000, method = "dpr", prop = 0.5)
rw <- simplifyGeom(soam, tolerance = 2000, method = "rw")

plot(soam, col = "black", lwd = 3)
plot(vr, col = "blue", add = TRUE)
plot(dp, col = "red", add = TRUE)
plot(dpr, col = "chartreuse", add = TRUE)
plot(rw, col = "orange", add = TRUE)

legend("bottom",
   xpd = NA,
   legend = c(
    "Original",
      "Vertex reduction",
      "Douglas-Peucker",
      "Douglas-Peucker reduction",
      "Reumann-Witkam"
  ),
  col = c("black", "blue", "red", "chartreuse", "orange"),
  lwd = c(3, 1, 1, 1, 1)
)

### Smooth geometry

hermite <- smoothGeom(soam, dist = 2000, angle = 3)
chaiken <- smoothGeom(soam, method = "Chaiken", dist = 2000)

plot(soam, col = "black", lwd = 2)
plot(hermite, col = "blue", add = TRUE)
plot(chaiken, col = "red", add = TRUE)

legend("bottom",
   xpd = NA,
   legend = c(
    "Original",
      "Hermite",
      "Chaiken"
  ),
  col = c("black", "blue", "red"),
  lwd = c(2, 1, 1, 1, 1)
)

### Clean geometry

# Has no effect on this vector!
noDangs <- removeDangles(soam, tolerance = 10000)

plot(soam, col = "black", lwd = 2)
plot(noDangs, col = "red", add = TRUE)

legend("bottom",
   xpd = NA,
   legend = c(
    "Original",
      "No dangles"
  ),
  lwd = c(2, 1),
  col = c("black", "red")
)

}