Improved activity diagrams.

design/duvenhage-inner-recursion-activity-diagram.puml

@@ -29,21 +29,26 @@
   skinparam ActivityFontSize                    11
 
   start
-  if (recursion depth > 30) then (yes)
+  if (recursion depth > 30?) then (yes)
     : search failed;
     stop
   endif
-  if (start and end point on same pixel) then (yes)
-    : return pixel intersection;
+  if (compare start and end point) then (same pixel)
+    : intersection ⇦ pixel intersection, with bilinear model;
+    : return intersection;
+    note left
+      this is the nominal return,
+      at final recursion level
+    end note
     stop
   endif
-  : compute kd-tree deepest level\ncontaining both start and end points;
+  :compute kd-tree deepest\nlevel sub-tile containing\nboth segment endpoints;
   if (compare segment and sub-tile maximum elevation) then (fully above)
     : return null;
-    note right
+    note left
       when the line-of-sight segment is fully above
       Digital Elevation Model, we can safely reject
-      it and proceed to next segment
+      it and proceed immediately to next segment
     end note
     stop
   endif
@@ -56,7 +61,7 @@
   end note
   repeat
     :intersection ⇦ recurse(previous, crossing);
-    if (found intersection?) then (yes)
+    if (intersection found?) then (yes)
       : return intersection;
       stop
     endif

design/duvenhage-top-loop-activity-diagram.puml

@@ -34,10 +34,10 @@
   : current point ⇦ null;
   : hmax ⇦ tile maximum elevation;
   while (current point is null)
-    : entry ⇦ point at altitude hmax;
-    if (locate entry point) then (in selected tile)
+    : current ⇦ point at altitude hmax;
+    if (locate current point) then (in selected tile)
     else (outside of selected tile)
-      : select tile containing entry point;
+      : select tile containing current point;
       : hmax ⇦ max(hmax, tile maximum elevation);
       : current point ⇦ null;
     endif
@@ -45,16 +45,16 @@
   repeat
     : exit ⇦ line-of-sight exit point from tile;
     : intersection ⇦ Duvenhage(current, exit);
-    if (found intersection?) then (yes)
+    if (intersection found?) then (yes)
       : return intersection;
       stop
     endif
-    if (tile exited at side?) then (no)
+    if (tile exit) then (bottom)
       : searching ⇦ false;
-    else (yes)
+    else (side)
       : forward point ⇦ point slightly after exit point;
       : select tile containing forward point;
-      if (DEM traversed between\ncurrent and forward points) then (yes)
+      if (DEM traversed between\ncurrent and forward points?) then (yes)
         : return current point;
         note right
          extremely rare case!