Data processing apparatus

1. A method of configuring data processing apparatus for automatically determining the real size of an object in an image of a scene displayed on a display screen, the method comprising:

responding to user input by displaying in the image of the scene displayed on the display screen a virtual object representative of a real size object to establish a first datum position, and storing data defining the first datum position;

varying a size of the virtual object in the image responsive to user input;

storing data representative of a horizontal and vertical size of the virtual object relative to the displayed image at the first datum position;

displaying said virtual object at a second datum position in said image responsive to user input and storing data defining the second datum position;

varying the size of the virtual object on the display screen at the second datum position responsive to user input; and

storing data representative of the vertical and horizontal size of the virtual object at the second datum position relative to the displayed image.

2. A method according to claim 1 , comprising automatically establishing said first datum position by displaying said virtual object such that the foot of the virtual object is at the foot of said displayed image.

3. A method according to claim 1 , further comprising automatically establishing said second datum position by displaying said virtual object such that the foot of the virtual object is on the horizon of the scene in the displayed image.

4. A method according to claim 1 , further comprising storing data representative of the real size represented by said virtual object.

5. A method as claimed in claim 1 , wherein the aspect ratio of the virtual object is maintained when the size of the virtual object is varied.

6. A method according to claim 1 , further comprising displaying said virtual object at an intermediate position between the first and second datum positions, which comprises interpolating the data representing the horizontal and vertical size of the virtual object in pixels from the first and the second datum positions.

7. Data processing apparatus configured for automatically determining a real size of an object in an image of a scene displayed on a display screen, the apparatus operative to:

respond to user input by displaying in the image of the scene displayed on the display screen a virtual object representative of a real size object to establish a first datum position and to store data defining the first datum position;

vary a size of the virtual object in the image responsive to user input;

store data representative of a horizontal and vertical size of the virtual object relative to the displayed image at the first datum position;

display said virtual object at a second datum position in said image responsive to user input and to store data defining the second datum position;

vary the size of the virtual object on the display screen at the second datum position responsive to user input; and

store data representative of the vertical and horizontal size of the virtual object at the second datum position relative to the displayed image.

8. Apparatus according to claim 7 , further operative to automatically establish said first datum position by displaying said virtual object such that the foot of the virtual object is at the foot of said displayed image.

9. Apparatus according to claim 7 , further operative to automatically establish said second datum position by displaying said virtual object such that the foot of the virtual object is on the horizon of the scene in the displayed image.

10. Apparatus according to claim 7 , further operative to store data representative of the real size represented by said virtual object.

11. Apparatus as claimed in claim 7 , further operative to maintain the aspect ratio of the virtual object when the size of the virtual object is varied.

12. Apparatus according to claim 7 , further operative to display said virtual object at an intermediate position between the first and second datum positions, and to interpolate the data representing the horizontal and vertical size of the virtual object in pixels from the first and the second datum positions.

13. A carrier carrying a computer program on a non-transitory computer readable media comprising processor implementable instructions for causing a computer to perform a method comprising:

responding to user input by displaying in an image of a scene displayed on a display screen a virtual object representative of a real size object to establish a first datum position, and storing data defining the first datum position;

varying a size of the virtual object in the image responsive to user input;

storing data representative of a horizontal and vertical size of the virtual object relative to the displayed image at the first datum position;

displaying said virtual object at a second datum position in said image responsive to user input and storing data defining the second datum position;

varying the size of the virtual object on the display screen at the second datum position responsive to user input; and

storing data representative of the vertical and horizontal size of the virtual object at the second datum position relative to the displayed image.

14. A carrier carrying the computer program on the non-transitory computer readable media according to claim 13 , comprising instructions for automatically establishing said first datum position by displaying said virtual object such that the foot of the virtual object is at the foot of said displayed image.

15. A carrier carrying the computer program on the non-transitory computer readable media according to claim 13 , further comprising instructions for automatically establishing said second datum position by displaying said virtual object such that the foot of the virtual object is on the horizon of the scene in the displayed image.

16. A carrier carrying the computer program on the non-transitory computer readable media according to claim 13 , further comprising instructions for storing data representative of the real size represented by said virtual object.

17. A carrying the computer program on the non-transitory computer readable media carrier as claimed in claim 13 , wherein the aspect ratio of the virtual object is maintained when the size of the virtual object is varied.

18. A carrier carrying the computer program on the non-transitory computer readable media according to claim 13 , further comprising instructions for displaying said virtual object at an intermediate position between the first and second datum positions, which comprises interpolating the data representing the horizontal and vertical size of the virtual object in pixels from the first and the second datum positions.