1. Spacecraft Stereo Imaging Systems Group S3

2. Variables Separation of the cameras Height of the cameras – relative to the bench Angle – The direction cameras are facing relative to each other

3. Other Considerations Distance – Between the object and the cameras. Size of the object

4. Theory of stereo images O d (x, y, z) f – focal length of the cameras. and are the points in the two images, produced by the cameras.

5. Theory of stereo images By considering the geometry of the system we can obtain a set of 3 simultaneous equations These equations can be rearranged to find equations for the coordinates of the object - x, y and z.

6. Theory of stereo images

7. The quantity, which appears in all the equations is known as disparity.

8. Stereo Views Left CameraRight Camera The objects are displaced in one image relative to the other. These displacements are known as DISPARITIES.

9. Producing Stereograms The optimal ratio of object distance to camera separation is 30/1. Separation of the camera the same as average human eyes. Displacement of objects inversely proportional to the distance

10. Initial Attempts at a Stereogram

12. Calibration The demagnification of the camera was found at a range of distances. This was done using a single camera. s h s´ h´ ObjectImage

13. Calibration where h is the height of the object h´ is the image height, s is the object distance and s´ is the image distance. The image height h´ is given by where n is the number of pixels and w is the width of 1 pixel (a single sensor) inside the camera.

14. Calibration By plotting a graph of the height in pixels, n, versus the distance s, for an object of known height, the constant s´/w can be found from the gradient, m.

15. Calibration Graph

16. Determination of Object Height and Range Now the ratio h/s can be found by measuring the image height in pixels … but more information is needed to distinguish between a small object which is close and a large object which is far away.

17. Finally We took some measurements of position in each of the two images and used them to find the x position of the object. We will continue this in the next lab session.