if (!inherits(mesh, "mesh3d"))

stop(deparse(substitute(mesh)), " is not a mesh3d object.")

edges <- NULL

if (length(mesh$it))

edges <- cbind(edges, mesh$it[1:2,], mesh$it[2:3,], mesh$it[c(3,1),])

if (length(mesh$ib))

edges <- cbind(edges, mesh$ib[1:2,], mesh$ib[2:3,], mesh$ib[3:4,], mesh$ib[c(4,1),])

if (ncol(edges)) {

# undirect the edges

uedges <- t(apply(edges, 2, sort))

dup <- duplicated(uedges) | duplicated(uedges, fromLast = TRUE)

edges <- edges[,!dup,drop=FALSE]

if (sorted) {

order <- rep(NA, ncol(edges))

order[1] <- 1

for (i in seq_len(length(order) - 1)) {

j <- which(edges[1,] == edges[2, order[i]])

j <- setdiff(j, order[1:i])

if (length(j))

order[i 1] <- j[1]

else

order[i 1] <- setdiff(1:length(order), order[1:i])

}

edges <- edges[, order, drop = FALSE]

}

}

result <- mesh3d(vertices = mesh$vb, segments = edges,

material = .fixMaterialArgs2(...))

if (simplify)

result <- cleanMesh3d(result)

result