diff --git a/src/BuildTiles/Main/construct.hxx b/src/BuildTiles/Main/construct.hxx
index 3defb05b..2c9ce99b 100644
--- a/src/BuildTiles/Main/construct.hxx
+++ b/src/BuildTiles/Main/construct.hxx
@@ -69,6 +69,10 @@ private:
     // with the UK grid
     bool useUKGrid;
 
+    // flag indicating whether this is a rebuild and Shared edge
+    // data should only be used for fitting, but not rewritten
+    bool writeSharedEdges;
+
     // detail level constraints
     int min_nodes;
     int max_nodes;
@@ -129,6 +133,10 @@ public:
     // UK grid flag
     inline bool get_useUKGrid() const { return useUKGrid; }
     inline void set_useUKGrid( const bool b ) { useUKGrid = b; }
+    
+    // shared edge write flag
+    inline bool get_write_shared_edges() const { return writeSharedEdges; }
+    inline void set_write_shared_edges( const bool b ) { writeSharedEdges = b; }
 
     // detail level constraints
     inline int get_min_nodes() const { return min_nodes; }
diff --git a/src/BuildTiles/Main/main.cxx b/src/BuildTiles/Main/main.cxx
index f13dd6e6..d235bfbe 100644
--- a/src/BuildTiles/Main/main.cxx
+++ b/src/BuildTiles/Main/main.cxx
@@ -951,7 +951,7 @@ static void do_custom_objects( const TGConstruct& c ) {
     char name[256];
 
     for ( int i = 0; i < (int)load_dirs.size(); ++i ) {
-	string base_dir = load_dirs[i] + "/" + b.gen_base_path();
+	string base_dir = c.get_work_base() + "/" + load_dirs[i] + "/" + b.gen_base_path();
 	string index_file = base_dir + "/" + b.gen_index_str() + ".ind";
 	cout << "collecting custom objects from " << index_file << endl;
 
@@ -1038,7 +1038,9 @@ static void construct_tile( TGConstruct& c ) {
     TGMatch m;
     m.load_neighbor_shared( c );
     m.split_tile( c );
-    m.write_shared( c );
+    if ( c.get_write_shared_edges() ) {
+            m.write_shared( c );
+    }
     m.assemble_tile( c );
 
     // now we must retriangulate the pasted together tile points
@@ -1099,6 +1101,7 @@ static void usage( const string name ) {
     cout << "  --ydist=<degrees>" << endl;
     cout << "  --nudge=<float>" << endl;
     cout << "  --useUKgrid" << endl;
+    cout << "  --no-write-shared-edges" << endl;
     cout << " ] <load directory...>" << endl;
     exit(-1);
 }
@@ -1118,6 +1121,10 @@ int main(int argc, char **argv) {
     // texture coordinate generation
     bool useUKgrid = false;
     
+    // flag indicating whether this is a rebuild and Shared edge
+    // data should only be used for fitting, but not rewritten
+    bool writeSharedEdges = true;
+    
     sglog().setLogLevels( SG_ALL, SG_DEBUG );
 
     //
@@ -1146,7 +1153,9 @@ int main(int argc, char **argv) {
 	} else if (arg.find("--cover=") == 0) {
 	    cover = arg.substr(8);
 	} else if (arg.find("--useUKgrid") == 0) {
-		useUKgrid = true;
+            useUKgrid = true;
+	} else if (arg.find("--no-write-shared-edges") == 0) {
+	    writeSharedEdges = false;
 	} else if (arg.find("--") == 0) {
 	    usage(argv[0]);
 	} else {
@@ -1209,6 +1218,7 @@ int main(int argc, char **argv) {
     c.set_work_base( work_dir );
     c.set_output_base( output_dir );
     c.set_useUKGrid( useUKgrid );
+    c.set_write_shared_edges( writeSharedEdges );
 
     c.set_min_nodes( 50 );
     c.set_max_nodes( (int)(TG_MAX_NODES * 0.8) );
diff --git a/src/BuildTiles/Match/match.cxx b/src/BuildTiles/Match/match.cxx
index df8d42f7..b4caa7c2 100644
--- a/src/BuildTiles/Match/match.cxx
+++ b/src/BuildTiles/Match/match.cxx
@@ -486,6 +486,13 @@ void TGMatch::write_shared( TGConstruct& c ) {
 	exit(-1);
     }
 
+    /*
+     * We only write data out for those sides for which the adjacent
+     * tiles still have to be built.
+     *
+     * If we have already read data for a given corner or side, this
+     * means that the adjacent tile already has been built.
+     */
     if ( ! sw_flag ) {
 	fprintf( fp, "sw_node %.6f %.6f %.6f\n", 
 		 sw_node.x(), sw_node.y(), sw_node.z() );
diff --git a/src/BuildTiles/Match/match.hxx b/src/BuildTiles/Match/match.hxx
index 5beaed82..f76431c8 100644
--- a/src/BuildTiles/Match/match.hxx
+++ b/src/BuildTiles/Match/match.hxx
@@ -52,6 +52,8 @@ private:
     point_list body_normals;
 
     // flags
+    // a flag is set if and only if we have read data for the given
+    // corner or side
     bool sw_flag, se_flag, ne_flag, nw_flag;
     bool north_flag, south_flag, east_flag, west_flag;