quadmesh (version 0.2.0)

triangulate_quads: Triangles from quads

Description

Convert quad index to triangles, this converts the 'rgl mesh3d (ib)' quad index to the complementary triangle index '(it)'.

Usage

triangulate_quads(quad_index)

Arguments

quad_index

the 'ib' index of quads from 'quadmesh'

Value

matrix of triangle indices

Details

Triangle pairs from each quad are interleaved in the result, so that neighbour triangles from a single quad are together.

Examples

# NOT RUN {
triangulate_quads(cbind(c(1, 2, 4, 3), c(3, 4, 6, 5)))

qm <- quadmesh(raster::crop(etopo, raster::extent(140, 160, -50, -30)))
tri <- triangulate_quads(qm$ib)
plot(t(qm$vb))
tri_avg <- colMeans(matrix(qm$vb[3, tri], nrow = 3), na.rm = TRUE)
scl <- function(x) (x - min(x))/diff(range(x))
tri_col <- grey(seq(0, 1, length = 100))[scl(tri_avg) * 99 + 1]
## tri is qm$ib converted to triangles for the same vertex set
polygon(t(qm$vb)[rbind(tri, NA), ])
polygon(t(qm$vb)[rbind(tri, NA), ], col = tri_col)
# }