Network surveillance system

1. A method for estimating the activity topology of a set of sensed data windows, each of the sensed data windows related to a corresponding sensed region, the method including the steps:

determining a subset of sensed data windows that are not connected by comparing sensed data windows pair wise from the set of sensed data windows, the pair wise comparison including determining whether a pair of sensed data windows does not have overlapping sensed regions by:

determining a first occupancy measure for a first sensed data window and a second occupancy measure for a second sensed data window, the first and second sensed data windows comprising the pair of sensed data windows, and

comparing the first and second occupancy measures by forming an occupancy vector corresponding to a first sensed data window sequence associated with the first sensed data window and a second occupancy vector corresponding to a second sensed data window sequence associated with the second sensed data window and comparing corresponding elements of the first and second occupancy vectors; and

excluding the subset of sensed data windows from the set of sensed data windows.

2. The method of claim 1 , wherein the step of comparing corresponding elements of the first and second occupancy vectors includes performing a vector exclusive-or operation on the first and second occupancy vectors to determine that the associated first and second sensed data windows do not overlap.

3. The method of claim 1 , wherein the second occupancy vector that corresponds to the second sensed data window sequence is based on the second sensed data window and its nearest neighbouring sensed data windows thereby forming a padded occupancy vector.

4. The method of claim 3 , wherein the step of comparing corresponding elements of the first and second occupancy vectors includes performing a vector exclusive-or operation on the first occupancy vector and the padded occupancy vector to determine that the associated first and second sensed data windows do not overlap.

5. The method of claim 3 , wherein the step of comparing corresponding elements of the first and second occupancy vectors includes performing a vector uni-directional exclusive-or operation on the first occupancy vector and the padded occupancy vector to determine that the associated first and second sensed data windows do not overlap.

6. The method of claim 1 , wherein the step of comparing corresponding elements of the first and second occupancy vectors includes comparing over neighbouring elements of one or both of the first and second occupancy vectors.

7. The method of claim 1 , wherein the step of determining whether a pair of sensed data windows does not have overlapping sensed regions includes taking into account the likelihood of a false indication that a pair of sensed data windows do overlap.

8. The method of claim 7 , wherein the step of taking into account the likelihood of a false indication that a pair of sensed data windows do overlap is based on previous data associated with the pair of sensed data windows.

9. The method of claim 7 , wherein the step of taking into account the likelihood of a false indication that a pair of sensed data windows do overlap includes taking into account an error rate of a sensor or sensors associated with the pair of sensed data windows.

10. The method of claim 1 , wherein the sensed data window is an image window and the first and second sensed data window sequences correspond to first and second image window sequences.

11. The method of claim 10 , wherein the first and second image window sequences correspond to respective time series of images.

12. The method of claim 11 , wherein the time series of images is provided by cameras in a network surveillance system.

13. The method of claim 1 , further including the step of determining a further subset of sensor data windows that are connected.

14. A network surveillance system including:

a network of sensors, each sensor providing one or more sensed data windows each corresponding to a sensed region and forming in total a set of sensed data windows; and

data processing means to:

determine a subset of sensed data windows that are not connected by comparing sensed data windows pair wise from the set of sensed data windows, the pair wise comparison including determining whether a pair of sensed data windows does not have overlapping sensed regions by:

determining a first occupancy measure for a first sensed data window and a second occupancy measure for a second sensed data window, the first and second sensed data windows comprising the pair of sensed data windows, and

comparing the first and second occupancy measures by forming an occupancy vector corresponding to a first sensed data window sequence associated with the first sensed data window and a second occupancy vector corresponding to a second sensed data window sequence associated with the second sensed data window and comparing corresponding elements of the first and second occupancy vectors; and

exclude the subset of sensed data windows from the set of sensed data windows.

15. A non-transitory program storage device readable by machine, tangibly embodying a program of instructions to perform method steps for estimating the activity topology of a set of sensed data windows, each of the sensed data windows related to a corresponding sensed region, the method steps including:

determining a subset of sensed data windows that are not connected by comparing sensed data windows pair wise from the set of sensed data windows, the pair wise comparison including determining whether a pair of sensed data windows does not have overlapping sensed regions by:

determining a first occupancy measure for a first sensed data window and a second occupancy measure for a second sensed data window, the first and second sensed data windows comprising the pair of sensed data windows, and

comparing the first and second occupancy measures by forming an occupancy vector corresponding to a first sensed data window sequence associated with the first sensed data window and a second occupancy vector corresponding to a second sensed data window sequence associated with the second sensed data window and comparing corresponding elements of the first and second occupancy vectors; and

excluding the subset of sensed data windows from the set of sensed data windows.

16. The method of claim 8 , wherein the step of taking into account the likelihood of a false indication that a pair of sensed data windows do overlap includes taking into account an error rate of a sensor or sensors associated with the pair of sensed data windows.

17. The network surveillance system of claim 14 , wherein comparing corresponding elements of the first and second occupancy vectors includes performing a vector exclusive-or operation on the first and second occupancy vectors to determine that the associated first and second sensed data windows do not overlap.

18. The network surveillance system of claim 14 , wherein the second occupancy vector that corresponds to the second sensed data window sequence is based on the second sensed data window and its nearest neighbouring sensed data windows thereby forming a padded occupancy vector.

19. The network surveillance system of claim 18 , wherein comparing corresponding elements of the first and second occupancy vectors includes performing a vector exclusive-or operation on the first occupancy vector and the padded occupancy vector to determine that the associated first and second sensed data windows do not overlap.

20. The network surveillance system of claim 18 , wherein comparing corresponding elements of the first and second occupancy vectors includes performing a vector uni-directional exclusive-or operation on the first occupancy vector and the padded occupancy vector to determine that the associated first and second sensed data windows do not overlap.

21. The network surveillance system of claim 14 , wherein comparing corresponding elements of the first and second occupancy vectors includes comparing over neighbouring elements of one or both of the first and second occupancy vectors.

22. The network surveillance system of claim 14 , wherein determining whether a pair of sensed data windows does not have overlapping sensed regions includes taking into account the likelihood of a false indication that a pair of sensed data windows do overlap.

23. The network surveillance system of claim 22 , wherein taking into account the likelihood of a false indication that a pair of sensed data windows do overlap is based on previous data associated with the pair of sensed data windows.

24. The network surveillance system of claim 22 , wherein the step of taking into account the likelihood of a false indication that a pair of sensed data windows do overlap includes taking into account an error rate of a sensor or sensors associated with the pair of sensed data windows.

25. The method of claim 23 , wherein the step of taking into account the likelihood of a false indication that a pair of sensed data windows do overlap includes taking into account an error rate of a sensor or sensors associated with the pair of sensed data windows.

26. The network surveillance system of claim 14 , wherein the network of sensors includes cameras, and wherein the sensed data window is an image window and the first and second sensed data window sequences correspond to first and second image window sequences.

27. The network surveillance system of claim 26 , wherein the first and second image window sequences correspond to respective time series of images.

28. The network surveillance system of claim 1 , wherein the data processor is operable to determine a further subset of sensor data windows that are connected.