spatialEco (version 2.0-1)

sa.trans: Trigonometric transformation of a slope and aspect interaction

Description

The Trigonometric Stage (1978) [slope * cos(aspect)] or [slope * sin(aspect)]

An a priori assumption of a maximum in the NW quadrant (45 azimuth) and a minimum in the SW quadrant can be replaced by an empirically determined location of the optimum without repeated calculations of the regression fit. In addition it is argued that expressions for the effects of aspect should always be considered as terms involving an interaction with slope (Stage, 1976)

For slopes from 0 bounded from -1 to 1. Greater than 100 out of the -1 to 1 range.

An alternative for slopes with values approaching infinity is to take the square root of slope/100 to reduce the range of values.By default this model test all values greater than 100 to 101

Usage

sa.trans(
  slope,
  aspect,
  type = "cos",
  slp.units = "degrees",
  asp.units = "degrees"
)

Value

A vector of the modeled value

Arguments

slope

slope values in degrees, radians or percent

aspect

aspect values in degrees or radians

type

Type of transformation, options are: "cos", "sin"

slp.units

Units of slope values, options are: "degrees", "radians" or "percent"

asp.units

Units of aspect values, options are: "degrees" or "radians"

Author

Jeffrey S. Evans <[e-mail]>

References

Stage, A. R. 1976. An Expression of the Effects of Aspect, Slope, and Habitat Type on Tree Growth. Forest Science 22(3):457-460.

Examples

 sa.trans(slope = 48.146, aspect = 360.000)

library(terra)
elev <- rast(system.file("extdata/elev.tif", package="spatialEco"))

# Example of slope*cos(aspect)
sa <- terra::terrain(elev, v=c("slope", "aspect"), unit="degrees")
scosa <- terra::lapp(c(sa[[1]], sa[[2]]), fun = sa.trans)