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Calculate direction

Source: R/internal.R
calc_direction.Rd

Internal function - not developed to be used outside of spatsoc functions

Usage

calc_direction(geometry_a, geometry_b, x_a, y_a, x_b, y_b, crs, use_transform)

Arguments

geometry_a, geometry_b

sfc (simple feature geometry list column) from get_geometry()

x_a, x_b

X coordinate column, numeric

y_a, y_b

Y coordinate column, numeric

crs

crs for x_a, y_a (and if provided, x_b, y_b) coordinates, ignored for geometry_a and geometry_b arguments

use_transform

boolean predetermine if coordinates/geometry need transform

Value

Direction in units of radians, in range of pi, -pi where North = 0.

Details

Calculate direction using lwgeom::st_geod_azimuth() between one of:

  • the sequence of points in geometry_a

  • the sequence of points in x_a, y_a

  • the pairwise points in geometry_a and geometry_b

  • the pairwise points in x_a, y_a and x_b, y_b

Requirements:

  • matching length between a and b objects if b provided

  • crs is provided. If crs is not longlat (as determined by sf::st_is_longlat()), the coordinates or geometry will be transformed to sf::st_crs(4326)

  • no missing values in coordinates

Examples

# Load data.table
library(data.table)

# Example result for East, North, West, South directions
example <- data.table(
  X = c(0, 5, 5, 0, 0),
  Y = c(0, 0, 5, 5, 0)
)
# E, N, W, S
example[, spatsoc:::calc_direction(x_a = X, y_a = Y, crs = 4326, use_transform = FALSE)]
#> Linking to GEOS 3.12.1, GDAL 3.8.4, PROJ 9.4.0; sf_use_s2() is TRUE
#> Units: [rad]
#> [1]  1.570796  0.000000 -1.566991  3.141593