Recursive curve simplification.

Helper from legacy INLA::inla.simplify.curve()

Attempts to simplify a polygonal curve by joining nearly colinear segments.

Uses a variation of the binary splitting Ramer-Douglas-Peucker algorithm, with an ellipse of half-width eps ellipse instead of a rectangle, motivated by prediction ellipse for Brownian bridge.

Usage

fm_simplify_helper(loc, idx, eps = NULL, eps_rel = NULL)

Arguments

loc

Coordinate matrix.

idx

Index vector into loc specifying a polygonal curve.

eps

Absolute straightness tolerance. Default NULL, no constraint.

eps_rel

Relative straightness tolerance. Default NULL, no constraint.

Value

An index vector into loc specifying the simplified polygonal curve.

Details

Variation of Ramer-Douglas-Peucker. Uses width epsilon ellipse instead of rectangle, motivated by prediction ellipse for Brownian bridge.

See also

Other nonconvex inla legacy support: fm_nonconvex_hull_inla(), fm_segm_contour_helper()

Author

Finn Lindgren finn.lindgren@gmail.com

Examples

theta <- seq(0, 2 * pi, length.out = 1000)
loc <- cbind(cos(theta), sin(theta))
idx <- fm_simplify_helper(loc = loc, idx = 1:nrow(loc), eps = 0.01)
print(c(nrow(loc), length(idx)))
#> [1] 1000   33
plot(loc, type = "l")
lines(loc[idx, ], col = "red")