Interpolate per-vertex attributes onto points

Linear (barycentric) interpolation of a matrix of per-vertex values from a triangle mesh onto query points. Points in no triangle take the nearest vertex's value. Used to carry attributes such as z onto Steiner vertices after refinement, matching the PA behaviour of RTriangle.

Usage

cdt_interpolate(P, T, A, xq, yq)

Arguments

P

vertex coordinates (n x 2)

T

triangle vertex indices (m x 3, 1-based)

A

per-vertex attribute matrix (n x k) or vector

xq, yq

query coordinates

Value

a length(xq) x k matrix (column names kept from A)

Examples

## two triangles on the unit square, z = x + y at the corners
P <- cbind(c(0, 1, 1, 0), c(0, 0, 1, 1))
T <- rbind(c(1, 2, 3), c(1, 3, 4))
A <- cbind(z = P[, 1] + P[, 2])
## a linear field is reproduced exactly inside; (2, 2) is outside
cdt_interpolate(P, T, A, xq = c(0.5, 0.25, 2), yq = c(0.5, 0.1, 2))
#>         z
#> [1,] 1.00
#> [2,] 0.35
#> [3,] 2.00