add which_side_of_line fn for #103

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: dodgr
 Title: Distances on Directed Graphs
-Version: 0.2.15.005
+Version: 0.2.15.006
 Authors@R: c(
     person("Mark", "Padgham", , "[email protected]", role = c("aut", "cre")),
     person("Andreas", "Petutschnig", role = "aut"),

R/RcppExports.R

@@ -249,6 +249,16 @@ rcpp_unique_rownames <- function(xyfrom, xyto, precision = 10L) {
     .Call(`_dodgr_rcpp_unique_rownames`, xyfrom, xyto, precision)
 }
 
+#' Determine which side of intersecting line a point lies on.
+#'
+#' @param (ax, ay) Coordinates of one end of line
+#' @param (bx, by) Coordinates of other end of line
+#' @param (x, y) Coordinates of point
+#' @return 0 if point on line, -1 if to the left; +1 if to the right.
+#'
+#' @noRd
+NULL
+
 #' Simple match of points to nearest vertices
 #' @noRd
 NULL

codemeta.json

@@ -7,7 +7,7 @@
   "codeRepository": "https://github.com/ATFutures/dodgr",
   "issueTracker": "https://github.com/ATFutures/dodgr/issues",
   "license": "https://spdx.org/licenses/GPL-3.0",
-  "version": "0.2.15.005",
+  "version": "0.2.15.006",
   "programmingLanguage": {
     "@type": "ComputerLanguage",
     "name": "R",

src/match-points.cpp

@@ -1,5 +1,20 @@
 #include "match-points.h"
 
+//' Determine which side of intersecting line a point lies on.
+//'
+//' @param (ax, ay) Coordinates of one end of line
+//' @param (bx, by) Coordinates of other end of line
+//' @param (x, y) Coordinates of point
+//' @return 0 if point on line, -1 if to the left; +1 if to the right.
+//'
+//' @noRd
+int which_side_of_line (const double ax, const double ay,
+        const double bx, const double by, const double x, const double y)
+{
+    double val = (bx - ax) * (y - ay) - (by - ay) * (x - ax);
+    return (val > 0) ? 1 : ((val < 0) ? -1 : 0);
+}
+
 //' Simple match of points to nearest vertices
 //' @noRd
 struct OnePointIndex : public RcppParallel::Worker

src/match-points.h

@@ -9,6 +9,9 @@ constexpr float INFINITE_FLOAT =  std::numeric_limits<float>::max ();
 constexpr double INFINITE_DOUBLE =  std::numeric_limits<double>::max ();
 constexpr int INFINITE_INT =  std::numeric_limits<int>::max ();
 
+int which_side_of_line (const double ax, const double ay,
+        const double bx, const double by, const double x, const double y);
+
 Rcpp::IntegerVector rcpp_points_index (const Rcpp::DataFrame &xy,
         Rcpp::DataFrame &pts);
 Rcpp::IntegerVector rcpp_points_to_edges_par (const Rcpp::DataFrame &graph,