From aa7bb37a99acf980de232fe5d6cbe70ee44a9cf2 Mon Sep 17 00:00:00 2001
From: Arndt Brenschede <Arndt.Brenschede@web.de>
Date: Tue, 30 Jul 2019 11:36:45 +0200
Subject: [PATCH] Douglas-Peucker transfer-node elimination on pre-processor
 level

---
 .../main/java/btools/mapcreator/DPFilter.java | 66 +++++++++++++++++++
 .../main/java/btools/mapcreator/OsmNodeP.java | 34 +++++-----
 2 files changed, 81 insertions(+), 19 deletions(-)
 create mode 100644 brouter-map-creator/src/main/java/btools/mapcreator/DPFilter.java

diff --git a/brouter-map-creator/src/main/java/btools/mapcreator/DPFilter.java b/brouter-map-creator/src/main/java/btools/mapcreator/DPFilter.java
new file mode 100644
index 0000000..b23d50b
--- /dev/null
+++ b/brouter-map-creator/src/main/java/btools/mapcreator/DPFilter.java
@@ -0,0 +1,66 @@
+/**
+ * Filter to eliminate some transfer nodes (Douglas-Peucker algorithm)
+ *
+ * @author ab
+ */
+package btools.mapcreator;
+
+import java.util.ArrayList;
+
+import btools.util.CheapRuler;
+
+public class DPFilter
+{
+  private static double dp_sql_threshold = 0.4 * 0.4;
+
+  /*
+   * for each node (except first+last), eventually set the DP_SURVIVOR_BIT
+   */
+  public static void doDPFilter( ArrayList<OsmNodeP> nodes, int first, int last )
+  {
+    double maxSqDist = -1.;
+    int index = -1;
+    OsmNodeP p1 = nodes.get( first );
+    OsmNodeP p2 = nodes.get( last );
+
+    double[] lonlat2m = CheapRuler.getLonLatToMeterScales( (p1.ilat+p2.ilat) >> 1 );
+    double dlon2m = lonlat2m[0];
+    double dlat2m = lonlat2m[1];
+    double dx = (p2.ilon - p1.ilon) * dlon2m;
+    double dy = (p2.ilat - p1.ilat) * dlat2m;
+    double d2 = dx * dx + dy * dy;
+    for ( int i = first + 1; i < last; i++ )
+    {
+      OsmNodeP p = nodes.get( i );
+      double t = 0.;
+      if ( d2 != 0f )
+      {
+        t = ( ( p.ilon - p1.ilon ) * dlon2m * dx + ( p.ilat - p1.ilat ) * dlat2m * dy ) / d2;
+        t = t > 1. ? 1. : ( t < 0. ? 0. : t );
+      }
+      double dx2 = (p.ilon - ( p1.ilon + t*( p2.ilon - p1.ilon ) ) ) * dlon2m;
+      double dy2 = (p.ilat - ( p1.ilat + t*( p2.ilat - p1.ilat ) ) ) * dlat2m;
+      double sqDist = dx2 * dx2 + dy2 * dy2;
+      if ( sqDist > maxSqDist )
+      {
+        index = i;
+        maxSqDist = sqDist;
+      }
+    }
+    if ( index >= 0 )
+    {
+      if ( index - first > 1 )
+      {
+        doDPFilter( nodes, first, index );
+      }
+      if ( maxSqDist >= dp_sql_threshold )
+      {
+        nodes.get( index ).bits |= OsmNodeP.DP_SURVIVOR_BIT;
+      }
+      if ( last - index > 1 )
+      {
+        doDPFilter( nodes, index, last );
+      }
+    }
+  }
+}
diff --git a/brouter-map-creator/src/main/java/btools/mapcreator/OsmNodeP.java b/brouter-map-creator/src/main/java/btools/mapcreator/OsmNodeP.java
index dde2704..dd70c65 100644
--- a/brouter-map-creator/src/main/java/btools/mapcreator/OsmNodeP.java
+++ b/brouter-map-creator/src/main/java/btools/mapcreator/OsmNodeP.java
@@ -35,6 +35,7 @@ public class OsmNodeP extends OsmLinkP
   public final static int TRAFFIC_BIT = 8;
   public final static int ANY_WAY_BIT = 16;
   public final static int MULTI_WAY_BIT = 32;
+  public final static int DP_SURVIVOR_BIT = 64;
 
   public byte bits = 0;
 
@@ -200,10 +201,15 @@ public class OsmNodeP extends OsmLinkP
       OsmNodeP origin = this;
       OsmNodeP target = null;
 
+      ArrayList<OsmNodeP> linkNodes = new ArrayList<OsmNodeP>();
+      linkNodes.add( this );
+
       // first pass just to see if that link is consistent
       while (link != null)
       {
         target = link.getTarget( origin );
+        linkNodes.add( target );
+
         if ( !target.isTransferNode() )
         {
           break;
@@ -244,30 +250,20 @@ public class OsmNodeP extends OsmLinkP
       mc.writeVarLengthSigned( target.ilon - ilon );
       mc.writeVarLengthSigned( target.ilat - ilat );
       mc.writeModeAndDesc( isReverse, link0.descriptionBitmap );
-      if ( !isReverse ) // write geometry for forward links only
+      if ( !isReverse && linkNodes.size() > 2 ) // write geometry for forward links only
       {
-        link = link0;
+        DPFilter.doDPFilter( linkNodes, 0, linkNodes.size()-1 );
         origin = this;
-        while (link != null)
+        for( int i=1; i<linkNodes.size()-1; i++ )
         {
-          OsmNodeP tranferNode = link.getTarget( origin );
-          if ( !tranferNode.isTransferNode() )
+          OsmNodeP tranferNode = linkNodes.get(i);
+          if ( ( tranferNode.bits & OsmNodeP.DP_SURVIVOR_BIT ) != 0 )
           {
-            break;
+            mc.writeVarLengthSigned( tranferNode.ilon - origin.ilon );
+            mc.writeVarLengthSigned( tranferNode.ilat - origin.ilat );
+            mc.writeVarLengthSigned( tranferNode.getSElev() - origin.getSElev() );
+            origin = tranferNode;
           }
-          mc.writeVarLengthSigned( tranferNode.ilon - origin.ilon );
-          mc.writeVarLengthSigned( tranferNode.ilat - origin.ilat );
-          mc.writeVarLengthSigned( tranferNode.getSElev() - origin.getSElev() );
-
-          // next link is the one (of two), does does'nt point back
-          for ( link = tranferNode.getFirstLink(); link != null; link = link.getNext( tranferNode ) )
-          {
-            if ( link.getTarget( tranferNode ) != origin )
-              break;
-          }
-          if ( link == null )
-            throw new RuntimeException( "follow-up link not found for transfer-node!" );
-          origin = tranferNode;
         }
       }
       mc.injectSize( sizeoffset );