[SpatialPartitioning] Clean up kdtree docs

Author: Amael Marquez

Ponca/src/SpatialPartitioning/KdTree/kdTree.h

@@ -272,19 +272,12 @@ public :
     NodeContainer m_nodes;
     IndexContainer m_indices;
 
-    LeafSizeType m_min_cell_size; ///< Minimal number of points per leaf
-    NodeIndexType m_leaf_count; ///< Number of leaves in the Kdtree (computed during construction)
+    LeafSizeType m_min_cell_size {64}; ///< Minimal number of points per leaf
+    NodeIndexType m_leaf_count {0}; ///< Number of leaves in the Kdtree (computed during construction)
 
     // Internal ----------------------------------------------------------------
 protected:
-    inline KdTreeImplBase():
-        m_points(),
-        m_nodes(),
-        m_indices(),
-        m_min_cell_size(64),
-        m_leaf_count(0)
-    {
-    }
+    inline KdTreeImplBase() = default;
 
     /// Generate a tree sampled from a custom contained type converted using a `Converter`
     /// \tparam PointUserContainer Input point, transformed to PointContainer

doc/src/ponca_module_spatialpartitioning.mdoc

@@ -12,7 +12,7 @@ namespace Ponca
 
   \subsection spatialpartitioning_intro_structures Datastructures
 
-   - Ponca::KdTreeDense and Ponca::KdTreeSparse : a binary search tree (https://en.wikipedia.org/wiki/K-d_tree)
+   - Ponca::KdTreeDense and Ponca::KdTreeSparse: binary search trees (https://en.wikipedia.org/wiki/K-d_tree)
    - Ponca::KnnGraph : a nearest neighbor graph (https://en.wikipedia.org/wiki/Nearest_neighbor_graph). Constructed from
    a KdTree.