flowDir: Path-Based Nondisperive Flow Direction

In terra: Spatial Data Analysis

Path-Based Nondisperive Flow Direction

Description

Computes nondispersive flow/drainage direction according to path-based methods over grid-based digital elevation models. This is an alternative to terrain(v="flowdir").

Usage

## S4 method for signature 'SpatRaster'
flowDir(x, lambda=0.5, deviation_type=c("ltd","lad"), max_iters=10^6, filename="", ...) 

Arguments

x	SpatRaster with elevation data
lambda	Parameter between 0 and 1
deviation_type	Character. Available options are "ltd" (the default) and "lad". If "ltd", nondispersive flow directions are determined using the least transversal deviation (LTD) criterion. If "lad", nondispersive flow directions are determined using the least angular deviation (LAD) criterion. See Orlandini et al. (2003) for details.
max_iters	maximum iterations for drainage path starting points detection
filename	character. Output filename
...	additional arguments for writing files as in writeRaster

Details

The algorithm is an adaptation of the one proposed by Li et al. (2022) and Orlandini et al. (2003). This function is experimental and under development: results are to be verified.

Value

SpatRaster

Author(s)

Emanuele Cordano

References

Orlandini, S., G. Moretti, M. Franchini, B. Aldighieri, and B. Testa (2003). Path-based methods for the determination of nondispersive drainage directions in grid-based digital elevation models, Water Resour. Res., 39, 1144, doi:10.1029/2002WR001639, 6. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2002WR001639

Li, Z., Shi, P., Yang, T., Wang, C., Yong, B., & Song, Y. (2022). An improved D8-LTD for the extraction of total contributing area (TCA) by adopting the strategies of path independency and local dispersion. Water Resources Research, 58, e2021WR030948. https://doi.org/10.1029/2021WR030948 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021WR030948

Useful presentation: http://www.idrologia.unimore.it/orlandini/web-archive/seminars/nyc-2008-2.pdf

See Also

terrain, watershed, flowAccumulation

Examples

elev1 <- array(NA,c(9,9))
elev2 <- elev1
dx <- 1
dy <- 1 
for (r in 1:nrow(elev1)) {
  y <- (r-5)*dx
  for (c in 1:ncol(elev1)) {
    x <- (c-5)*dy
    elev1[r,c] <- 5*(x^2+y^2)
    elev2[r,c] <- 10+5*(abs(x))-0.001*y 
  }
} 

## Elevation raster
elev1 <- rast(elev1)
elev2 <- rast(elev2)

t(array(elev1[],rev(dim(elev1)[1:2])))
t(array(elev2[],rev(dim(elev2)[1:2])))

plot(elev1)
plot(elev2)

## Flow direction raster
fdir1 <- flowDir(elev1, lambda=1)
fdir2 <- flowDir(elev2, lambda=1)

elev <- rast(system.file('ex/elev.tif',package="terra"))

fdirlad1 <- flowDir(elev, lambda=0.5, deviation_type="lad")
fdirlad2 <- flowDir(elev, lambda=0.5, deviation_type="lad")

terra documentation built on Aug. 22, 2026, 5:07 p.m.