Better comment on path elimination logic.

Move init/finish to unnamed namespace in Geometry.

include/pdal/Geometry.hpp

@@ -76,11 +76,6 @@ static void GEOSWarningHandler(const char *fmt, ...)
     va_end(args);
 }
 
-} // Unnamed namespace
-
-namespace Geometry
-{
-
 static GEOSContextHandle_t init()
 {
     if (s_contextCnt == 0)
@@ -96,6 +91,11 @@ static void finish()
         finishGEOS_r(s_environment);
 }
 
+} // Unnamed namespace
+
+namespace Geometry
+{
+
 static std::string smoothPolygon(const std::string& wkt, double tolerance)
 {
     GEOSContextHandle_t env = init();

plugins/hexbin/filters/HexBin.cpp

@@ -143,10 +143,19 @@ void HexBin::done(PointTableRef table)
     m_metadata.add("boundary", polygon.str(),
         "Boundary MULTIPOLYGON of domain");
 
-    const double SQRT_3(1.732050808);
-    // This is just a little longer than the prependicular distance of the
-    // "humps."
-//    double tolerance = 1.1 * m_grid->height() / (2 * SQRT_3);
+    // We want to make these bumps on edges go away, which means that
+    // we want to elimnate both B and C.  If we take a line from A -> C,
+    // we need the tolerance to eliminate B.  After that we're left with
+    // the triangle ACD and we want to eliminate C.  The perpendicular
+    // distance from AD to C is the hexagon height / 2, so we set the
+    // tolerance a little larger than that.  This is larger than the
+    // perpendicular distance needed to eliminate B in ABC, so should
+    // serve for both cases.
+    //
+    //     B ______  C
+    //      /      \
+    //   A /        \ D
+    //
     double tolerance = 1.1 * m_grid->height() / 2;
     m_metadata.add("smoothed_boundary",
         Geometry::smoothPolygon(polygon.str(), tolerance),