Convert degrees between 'north-orientation' and 'east orientation'

This function converts facing between "north orientation" and "east orientation".

In "north orientation" systems, a 0-degree facing is north, and the angle of facing proceeds clockwise. For example, a 90 degree facing faces east, 180 south, and 270 west. In "east orientation", a 0-degree facing is east, and the facing angle proceeds counter-clockwise. For example, 90 is north, 180 is west, and 270 south.

Usage

# S4 method for class 'GRaster'
reorient(x, units = "degrees")

# S4 method for class 'numeric'
reorient(x, units = "degrees")

Arguments

x

A numeric vector or a GRaster with cell values equal to facing (in degrees).

units

Character: "Units" of values in x: either "degrees" for degrees (default) or "radians". Partial matching is used.

Value

A GRaster or numeric vector. Values will be in the range between 0 and 360 and represents facing in the system "opposing" the input's system. For example, if the input is north orientation, the output will be east orientation. If the input is in east orientation, the output will be in north orientation.

Examples

### Re-orient numeric values:
facings <- c(0, 90, 180, 270, 360)
reorient(facings)
#> [1]  90   0 270 180  90

# Re-reorienting returns the same values:
reorient(reorient(facings))
#> [1]   0  90 180 270   0

if (grassStarted()) {

### Re-orient a GRaster:

# Setup
library(terra)
madElev <- fastData("madElev")
elev <- fast(madElev)

# Calculate aspect in degrees, using north orientation:
aspectNorth <- terrain(elev, "aspect")

# Re-orient to east-facing:
aspectEast <- reorient(aspectNorth)

# Re-reorienting is the same, to within rounding error:
aspectNorth - reorient(reorient(aspectNorth))

# Plot:
aspects <- c(aspectNorth, aspectEast)
names(aspects) <- c("north_orientation", "east_orientation")
plot(aspects)


}