--- branches/development/src/brains/Snapshot.cpp	2012/07/03 18:32:27	1764
+++ branches/development/src/brains/Snapshot.cpp	2012/10/22 20:42:10	1808
@@ -44,7 +44,6 @@
  * @file Snapshot.cpp
  * @author tlin
  * @date 11/11/2004
- * @time 10:56am
  * @version 1.0
  */
 
@@ -73,7 +72,8 @@ namespace OpenMD {
     frameData.lrPotentials = potVec(0.0);
     frameData.excludedPotentials = potVec(0.0); 
     frameData.restraintPotential = 0.0; 
-    frameData.rawPotential = 0.0;       
+    frameData.rawPotential = 0.0;   
+    frameData.xyArea = 0.0;
     frameData.volume = 0.0;          
     frameData.thermostat = make_pair(0.0, 0.0);
     frameData.electronicThermostat = make_pair(0.0, 0.0);
@@ -104,6 +104,7 @@ namespace OpenMD {
     frameData.excludedPotentials = potVec(0.0); 
     frameData.restraintPotential = 0.0; 
     frameData.rawPotential = 0.0;       
+    frameData.xyArea = 0.0;
     frameData.volume = 0.0;          
     frameData.thermostat = make_pair(0.0, 0.0);
     frameData.electronicThermostat = make_pair(0.0, 0.0);
@@ -138,7 +139,8 @@ namespace OpenMD {
     hasKineticEnergy = false;       
     hasShortRangePotential = false;
     hasLongRangePotential = false;
-    hasPotentialEnergy = false;     
+    hasPotentialEnergy = false;   
+    hasXYarea = false;
     hasVolume = false;         
     hasPressure = false;       
     hasTemperature = false;    
@@ -247,6 +249,16 @@ namespace OpenMD {
   /** Returns the inverse H-Matrix */
   Mat3x3d Snapshot::getInvHmat() {
     return frameData.invHmat;
+  }
+
+  RealType Snapshot::getXYarea() {
+    if (!hasXYarea) {
+      Vector3d x = frameData.hmat.getColumn(0);
+      Vector3d y = frameData.hmat.getColumn(1);
+      frameData.xyArea = cross(x,y).length();
+      hasXYarea = true;
+    }
+    return frameData.xyArea;
   }
 
   RealType Snapshot::getVolume() {