Resample a path at a fixed arc length step

Walks along a path and emits a point every step units of arc length. The result has (nearly) uniform point spacing regardless of how the input was parameterized, which is what makes a swept tube look even: generate_tube places exactly one cross-section per path point, so uneven spacing means a tube that is finely subdivided in one place and faceted in another. Typical use is to even out the output of spline_path, whose samples are evenly spaced in the curve parameter rather than along the curve.

Usage

resample_path(path, step, closed = FALSE)

Arguments

path

Nx3 numeric matrix of path points (or a length-3 vector).

step

Arc length between samples. Must be a single positive number; other values return the path unchanged.

closed

Whether the path loops back to its first point (default FALSE).

Value

An Nx3 numeric matrix of resampled path points. A path without length (or with fewer than two points) is returned as it is.

Details

The spacing that is uniform is the *arc length* along the path; the straight-line distances between consecutive samples are slightly shorter wherever the path curves. An open path always keeps its final point (with a possibly shorter last step); a closed path ends on a copy of its first point and is covered in a whole number of steps, so its effective step can differ from the requested one by a fraction of a percent.

See also

path_length, spline_path

Examples

waypoints <- matrix(c(0, 0, 0, 1, 1, 0, 2, 0, 0), ncol = 3, byrow = TRUE)
smooth <- spline_path(waypoints, samples_per_segment = 32)
even <- resample_path(smooth, step = 0.1)
nrow(even)
#> [1] 30