Add WKB support for POINT EMPTY

modules/core/src/main/java/org/locationtech/jts/io/WKBReader.java

@@ -34,9 +34,12 @@
  * with arbitrary byte stream sources.
  * <p>
  * This class reads the format describe in {@link WKBWriter}.  
- * It also partially handles
+ * It partially handles
  * the <b>Extended WKB</b> format used by PostGIS, 
  * by parsing and storing SRID values.
+ * Although not defined in the WKB spec, empty points
+ * are handled if they are represented as a Point with <code>NaN</code> X and Y ordinates.
+ * <p>
  * The reader repairs structurally-invalid input
  * (specifically, LineStrings and LinearRings which contain
  * too few points have vertices added,
@@ -254,6 +257,10 @@ private Geometry setSRID(Geometry g, int SRID)
   private Point readPoint() throws IOException
   {
     CoordinateSequence pts = readCoordinateSequence(1);
+    // If X and Y are NaN create a empty point
+    if (Double.isNaN(pts.getX(0)) || Double.isNaN(pts.getY(0))) {
+      return factory.createPoint();
+    }
     return factory.createPoint(pts);
   }
 

modules/core/src/main/java/org/locationtech/jts/io/WKBWriter.java

@@ -44,9 +44,7 @@
  * by setting the third bit of the <tt>wkbType</tt> word.
  * EWKB format is upward compatible with the original SFS WKB format.
  * <p>
- * Empty Points cannot be represented in WKB; an
- * {@link IllegalArgumentException} will be thrown if one is
- * written. 
+ * Empty Points are output as a Point with <code>NaN</code> X and Y ordinate values. 
  * <p>
  * The WKB specification does not support representing {@link LinearRing}s;
  * they will be written as {@link LineString}s.
@@ -330,11 +328,13 @@ else if (geom instanceof GeometryCollection)
 
   private void writePoint(Point pt, OutStream os) throws IOException
   {
-    if (pt.getCoordinateSequence().size() == 0)
-      throw new IllegalArgumentException("Empty Points cannot be represented in WKB");
     writeByteOrder(os);
     writeGeometryType(WKBConstants.wkbPoint, pt, os);
-    writeCoordinateSequence(pt.getCoordinateSequence(), false, os);
+    if (pt.getCoordinateSequence().size() == 0) {
+      writeNaNs(2, os);
+    } else {
+      writeCoordinateSequence(pt.getCoordinateSequence(), false, os);
+    }
   }
 
   private void writeLineString(LineString line, OutStream os)
@@ -424,4 +424,13 @@ private void writeCoordinate(CoordinateSequence seq, int index, OutStream os)
       os.write(buf, 8);
     }
   }
+
+  private void writeNaNs(int numNaNs, OutStream os)
+      throws IOException
+  {
+    for (int i = 0; i < numNaNs; i++) {
+      ByteOrderValues.putDouble(Double.NaN, buf, byteOrder);
+      os.write(buf, 8);
+    }
+  }
 }

modules/core/src/test/java/org/locationtech/jts/io/WKBTest.java

@@ -57,7 +57,11 @@ public void testPointPCS() throws IOException, ParseException {
 	public void testPoint() throws IOException, ParseException {
 		runWKBTest("POINT (1 2)");
 	}
-
+
+  public void testPointEmpty() throws IOException, ParseException {
+    runWKBTest("POINT EMPTY");
+  }
+
 	public void testLineString()
       throws IOException, ParseException
   {