R/internal.R

In delaunay: 2d, 2.5d, and 3d Delaunay Tessellations

distance <- function(A, B){
  sqrt(c(crossprod(A-B)))
}

triangleArea <- function(A, B, C){
  a <- distance(B, C)
  b <- distance(A, C)
  c <- distance(A, B)
  s <- (a + b + c) / 2
  sqrt(s*(s-a)*(s-b)*(s-c))
}

delaunayArea <- function(vertices, triangles){
  ntriangles <- nrow(triangles)
  areas <- numeric(ntriangles)
  for(i in 1L:ntriangles){
    points <- vertices[triangles[i, ], ]
    areas[i] <- triangleArea(points[1L, ], points[2L, ], points[3L, ])
  }
  sum(areas)
}

makeTriangle <- function(vertices, indices){
  vertices[indices, ]
}

subtractEdges <- function(Edges, edges){
  if(is.null(edges)){
    return(Edges)
  }
  if(nrow(Edges) == nrow(edges)){
    return(NULL)
  }
  Strings <- paste0(Edges[, 1L], "-", Edges[, 2L])
  strings <- paste0(edges[, 1L], "-", edges[, 2L])
  rownames(Edges) <- Strings
  keep <- setdiff(Strings, strings)
  Edges[keep, ]
}

unionEdges <- function(edges1, edges2){
  if(is.null(edges2)){
    return(edges1)
  }
  Edges <- rbind(edges1, edges2)
  Edges[!duplicated(Edges), ]
  # strings1 <- paste0(edges1[, 1L], "-", edges1[, 2L])
  # strings2 <- paste0(edges2[, 1L], "-", edges2[, 2L])
  # strings <- union(strings1, strings2)
}