Centerline interpolation

Quite often it is necessary to interpolate a line between two other lines. A centerline between two banks is one example.

Since curvatures of both lines (banks) can differ significantly, it is not taken into account, but spatial proximity only.

This tool can handle degenerate geometries in general case, .e.g self intersecting.

library(rgdal)
library(lattice)
Bank_1 <- readOGR("..", "bank1")
Bank_2 <- readOGR("..", "bank2")
spar <- 0.4
Step_pattern <- "symmetricP05"
Step <- 25
Fraction <- .9
ff <- function(Fraction) {
  source('~/.qgis2/processing/rscripts/Banks to centerline.rsx', TRUE)
  Centerline@lines[[1]]@ID <- as.character(Fraction)
  rownames(Centerline@data) <- as.character(Fraction)
  Centerline@data$Fraction <- Fraction
  Centerline
}
l <- lapply(seq(.1, .9, .1), ff)
ll <- do.call('rbind.SpatialLinesDataFrame', l)
trellis.par.set(sp.theme())
spplot(ll, 'Fraction', panel=function(...){
  panel.polygonsplot(...)
  sp.lines(Bank_1, col='ForestGreen', lwd=2)
  sp.lines(Bank_2, col='ForestGreen', lwd=2)
})

Figure 1: Line interpolation for various fractions