Marching-triangle threshold segments

Computes exact linear threshold crossings from the same vertex-scalar model used by [render_surface_rgba()]. Positive and negative levels are handled as independent regions for two-sided maps.

Usage

surface_threshold_segments(
  vertices,
  faces,
  values,
  threshold,
  tail = c("two_sided", "positive", "negative")
)

Arguments

vertices

N by 2 or N by 3 projected vertex coordinates.

faces

F by 3 one-based vertex indices.

values

Numeric scalar per vertex.

threshold

Positive threshold magnitude.

tail

Two-sided, positive, or negative levels.

Value

A data frame with two rows per threshold segment.