--- a/scripts/display-trajectories.py	Fri Jul 12 01:26:22 2013 -0400
+++ b/scripts/display-trajectories.py	Fri Jul 12 02:29:49 2013 -0400
@@ -17,6 +17,7 @@
 
 args = parser.parse_args()
 
+homography = None
 if args.configFilename: # consider there is a configuration file
     params = utils.TrackingParameters()
     params.loadConfigFile(args.configFilename)
@@ -24,12 +25,14 @@
     databaseFilename = params.databaseFilename
     homography = inv(params.homography)
     firstFrameNum = params.firstFrameNum
-else:
+
+if args.videoFilename != None:
     videoFilename = args.videoFilename
+if args.databaseFilename != None:
     databaseFilename = args.databaseFilename
-    homography = None
-    if args.homography:
-        homography = inv(loadtxt(args.homography))            
+if args.homography != None:
+    homography = inv(loadtxt(args.homography))            
+if args.firstFrameNum != None:
     firstFrameNum = args.firstFrameNum
 
 objects = storage.loadTrajectoriesFromSqlite(databaseFilename, args.trajectoryType)