Converts a spherical direction given as azimuth and elevation into the
length-3 direction vector used by coord_3d() and light(). Both of those
arguments take a vector of the form c(x, y, z) whose magnitude is ignored;
direction() is an alternative way to express such a vector for people who
find angles easier to reason about than components.
Details
Azimuth is a compass-style bearing measured clockwise from the positive y
axis, matching the convention used by terrain shading functions such as
terra::shade(). Elevation is measured upward from the xy plane, so
elevation = 90 points along the positive z axis and elevation = -90
points along the negative z axis.
The returned vector is scaled to unit length, but since both coord_3d() and
light() normalize their inputs, the magnitude carries no meaning.
See also
coord_3d() and light(), which accept the result.
Examples
# The default viewing angle, expressed as a direction
direction(210, 30)
#> [1] -0.4330127 -0.7500000 0.5000000
# The default lighting angle
direction(270, 63.43)
#> [1] -4.472908e-01 -8.216600e-17 8.943886e-01
# Light from directly overhead
light(direction = direction(0, 90))
#> Lighting specification:
#> Method: diffuse
#> Direction: [ 0, 6.12323399573677e-17, 1 ] (directional lighting)
#> azimuth: 180 deg, elevation: 90 deg
#> anchor: scene
#> Shading: fill + color (contrast = 1 , mode = hsv )