fix: ramer_douglas_peucker Q output is MatrixXd not VectorXi

Author: jf---

src/compas_libigl/simplify.py

@@ -18,11 +18,11 @@ def ramer_douglas_peucker(points, threshold):
 
     Returns
     -------
-    tuple[list[list[float]], list[int], list[int]]
+    tuple[list[list[float]], list[int], list[list[float]]]
         A tuple containing
-        * the simplified polyline points,
-        * indices in original polyline that were kept,
-        * for each simplified point, its index in the original polyline.
+        * the simplified polyline points (S),
+        * indices in original polyline that were kept (J),
+        * for each original point, the corresponding point on the simplified curve (Q).
     """
     P = np.asarray(points, dtype=np.float64)
     S, J, Q = _simplify.ramer_douglas_peucker(P, float(threshold))

src/simplify.cpp

@@ -1,18 +1,19 @@
 #include "simplify.hpp"
 
-std::tuple<compas::RowMatrixXd, Eigen::VectorXi, Eigen::VectorXi>
+std::tuple<compas::RowMatrixXd, Eigen::VectorXi, compas::RowMatrixXd>
 ramer_douglas_peucker(
     Eigen::Ref<const compas::RowMatrixXd> P,
     double threshold
 ) {
     Eigen::MatrixXd S;  // Simplified polyline
     Eigen::VectorXi J;  // Indices of kept points in original polyline
-    Eigen::VectorXi Q;  // For each point in S, index in original P
+    Eigen::MatrixXd Q;  // For each point in original P, the corresponding point on simplified curve
 
     igl::ramer_douglas_peucker(P, threshold, S, J, Q);
 
     compas::RowMatrixXd S_row = S;
-    return std::make_tuple(S_row, J, Q);
+    compas::RowMatrixXd Q_row = Q;
+    return std::make_tuple(S_row, J, Q_row);
 }
 
 NB_MODULE(_simplify, m) {

src/simplify.hpp

@@ -9,9 +9,9 @@
  *
  * @param P #P x 3 matrix of polyline points
  * @param threshold Maximum distance threshold for simplification
- * @return Tuple of (simplified points, indices of kept points, mapping from simplified to original)
+ * @return Tuple of (simplified points, indices of kept points, mapping from original to simplified)
  */
-std::tuple<compas::RowMatrixXd, Eigen::VectorXi, Eigen::VectorXi>
+std::tuple<compas::RowMatrixXd, Eigen::VectorXi, compas::RowMatrixXd>
 ramer_douglas_peucker(
     Eigen::Ref<const compas::RowMatrixXd> P,
     double threshold);