diff --git a/c_tools/analysis/voidOverlap.cpp b/c_tools/analysis/voidOverlap.cpp
index 0450e25..d96f75e 100644
--- a/c_tools/analysis/voidOverlap.cpp
+++ b/c_tools/analysis/voidOverlap.cpp
@@ -93,7 +93,8 @@ void loadCatalog(const char *partFile, const char *volFile,
                  const char *voidFile, const char *zoneFile,
                  const char *infoFile, const char *centerFile,
                  const char *shapeFile,
-                 const char *zonePartFile, CATALOG& catalog);
+                 const char *zonePartFile, CATALOG& catalog,
+                 bool isObservation);
 
 float getDist(CATALOG& catalog1, CATALOG& catalog2, int& iVoid1, int& iVoid2,
                bool periodicX, bool periodicY, bool operiodicZ);
@@ -148,12 +149,12 @@ int main(int argc, char **argv) {
   loadCatalog(args.partFile1_arg, args.volFile1_arg, args.voidFile1_arg,
               args.zoneFile1_arg, args.infoFile1_arg, args.centerFile1_arg,
               args.shapeFile1_arg,
-              args.zonePartFile1_arg, catalog1);
+              args.zonePartFile1_arg, catalog1, args.isObservation_flag);
 
   loadCatalog(args.partFile2_arg, args.volFile2_arg, args.voidFile2_arg,
               args.zoneFile2_arg, args.infoFile2_arg, args.centerFile2_arg,
               args.shapeFile2_arg,
-              args.zonePartFile2_arg, catalog2);
+              args.zonePartFile2_arg, catalog2, args.isObservation_flag);
 
   // check for periodic box
     if ( strchr(args.periodic_arg, 'x') != NULL) {
@@ -532,11 +533,12 @@ void loadCatalog(const char *partFile, const char *volFile,
                  const char *voidFile, const char *zoneFile,
                  const char *infoFile, const char *centerFile,
                  const char *shapeFile,
-                 const char *zonePartFile, CATALOG& catalog) {
+                 const char *zonePartFile, CATALOG& catalog,
+                 bool isObservation) {
 
-  int i, p, numPartTot, numZonesTot, dummy, iVoid, iZ, numVolTot;
+  int i, p, numPartTot, numZonesTot, dummy, iVoid, iZ, numVolTot, zoneNumPart;
   FILE *fp;
-  float *temp, junk, voidVol, coreParticle, coreDens, zoneVol, zoneNumPart;
+  float *temp, junk, voidVol, coreParticle, coreDens, zoneVol;
   float densCon, voidProb, volNorm;
   long *temp2;
   int junkInt, voidID, numPart, numZones, zoneID, partID;
@@ -676,10 +678,18 @@ void loadCatalog(const char *partFile, const char *volFile,
     //       &tempFloat, &tempFloat, &tempFloat, &tempFloat, &tempInt,
     //       &tempFloat, &tempInt, &tempInt, &tempInt, &tempInt);
 
+    // convert back to ZOBOV-normalized units
 //if (iVoid < 10) printf("BARY %d %d %e %e %e\n", iVoid, catalog.voids[iVoid].voidID, tempBary[0], tempBary[1], tempBary[2]);
     tempBary[0] = (tempBary[0] - ranges[0][0])/catalog.boxLen[0];
     tempBary[1] = (tempBary[1] - ranges[1][0])/catalog.boxLen[1];
     tempBary[2] = (tempBary[2] - ranges[2][0])/catalog.boxLen[2];
+
+    if (isObservation) {
+      tempBary[0] -= 0.5;
+      tempBary[1] -= 0.5;
+      tempBary[2] -= 0.5;
+    }
+
     catalog.voids[iVoid].macrocenter[0] = tempBary[0];
     catalog.voids[iVoid].macrocenter[1] = tempBary[1];
     catalog.voids[iVoid].macrocenter[2] = tempBary[2];
diff --git a/c_tools/analysis/voidOverlap.ggo b/c_tools/analysis/voidOverlap.ggo
index e5e3f94..97e9496 100644
--- a/c_tools/analysis/voidOverlap.ggo
+++ b/c_tools/analysis/voidOverlap.ggo
@@ -24,6 +24,7 @@ option "centerFile2" - "Barycenter file for catalog 2" string yes
 option "shapeFile2" - "Shape file for catalog 2" string yes
 
 # options
+option "isObservation" - "We are working with observational data" flag off
 option "outfile" - "Output file" string yes
 option "useID" - "Use unique catalog ID to match voids; otherwise use volumes" flag off
 option "overlapFrac" - "threshold fraction of voronoi radius to count as matched" double optional default="0.25"
diff --git a/python_tools/void_python_tools/backend/launchers.py b/python_tools/void_python_tools/backend/launchers.py
index 803d810..c603e58 100644
--- a/python_tools/void_python_tools/backend/launchers.py
+++ b/python_tools/void_python_tools/backend/launchers.py
@@ -557,6 +557,9 @@ def launchVoidOverlap(sample1, sample2, sample1Dir, sample2Dir,
   else:
     matchPrefix = "trimmed_nodencut_"
 
+  if sample1.dataType == "observation" or sample2.dataType == "observation":
+    observationLine = " --isObservation"
+
   if not (continueRun and jobSuccessful(logFile, "Done!\n")):
     cmd = binPath
     cmd += " --partFile1=" + sample1Dir+"/zobov_slice_" + \
@@ -595,6 +598,8 @@ def launchVoidOverlap(sample1, sample2, sample1Dir, sample2Dir,
 
     cmd += " --overlapFrac=" + str(overlapFrac)
 
+    cmd += observationLine
+
     if matchMethod == "useID": cmd += " --useID"
     cmd += periodicLine
     cmd += " --outfile=" + outputFile
@@ -605,11 +610,11 @@ def launchVoidOverlap(sample1, sample2, sample1Dir, sample2Dir,
     subprocess.call(cmd, stdout=log, stderr=log, shell=True)
     log.close()
 
-    if jobSuccessful(logFile, "Done!\n"):
-      print "done"
-    else:
-      print "FAILED!"
-      exit(-1)
+    #if jobSuccessful(logFile, "Done!\n"):
+    print "done"
+    #else:
+    #  print "FAILED!"
+    #  exit(-1)
 
   else:
     print "already done!"