Calculate the angular difference between lines and a predefined bearing

This function was designed to find lines that are close to parallel and perpendicular to some pre-defined route. It can return results that are absolute (contain information on the direction of turn, i.e. + or - values for clockwise/anticlockwise), bidirectional (which mean values greater than +/- 90 are impossible).

Usage

angle_diff(l, angle, bidirectional = FALSE, absolute = TRUE)

Arguments

l

A spatial lines object

angle

an angle in degrees relative to North, with 90 being East and -90 being West. (direction of rotation is ignored).

bidirectional

Should the result be returned in a bidirectional format? Default is FALSE. If TRUE, the same line in the oposite direction would have the same bearing

absolute

If TRUE (the default) only positive values can be returned

Details

Building on the convention used in in the bearing() function from the geosphere package and in many applications, North is definied as 0, East as 90 and West as -90.

See also

Other lines: geo_toptail(), is_linepoint(), line2df(), line2points(), line_bearing(), line_breakup(), line_midpoint(), line_segment(), line_segment1(), line_via(), mats2line(), n_segments(), n_vertices(), onewaygeo(), points2line(), toptail_buff()

Examples

lib_versions <- sf::sf_extSoftVersion()
lib_versions
#>           GEOS           GDAL         proj.4 GDAL_with_GEOS     USE_PROJ_H 
#>       "3.12.1"        "3.8.4"        "9.4.0"         "true"         "true" 
#>           PROJ 
#>        "9.4.0" 
# fails on some systems (with early versions of PROJ)
if (lib_versions[3] >= "6.3.1") {
  # Find all routes going North-South
  lines_sf <- od2line(od_data_sample, zones = zones_sf)
  angle_diff(lines_sf[2, ], angle = 0)
  angle_diff(lines_sf[2:3, ], angle = 0)
}
#> Creating centroids representing desire line start and end points.
#> Linking to GEOS 3.12.1, GDAL 3.8.4, PROJ 9.4.0; sf_use_s2() is TRUE
#> [1]  92.2313 105.0539