Distance-varying illumination and imaging techniques for depth mapping

1. A method for mapping, comprising:

projecting a pattern onto an object via an astigmatic optical element having different, respective focal lengths in different meridional planes of the element;

capturing an image of the pattern on the object; and

processing the image so as to derive a three-dimensional (3D) map of the object based on features of the image that vary responsively to the different focal lengths.

2. The method according to claim 1 , wherein the astigmatic optical element comprises a combination of at least two cylindrical lens surfaces in different, respective orientations.

3. The method according to claim 1 , wherein the astigmatic optical element comprises a diffractive optical element.

4. The method according to claim 1 , wherein the astigmatic optical element comprises an off-axis element.

5. A method for mapping, comprising:

directing light via an aperture so as to project onto an object a diffraction pattern characterized by a transition from near-field to far-field diffraction;

capturing an image of the diffraction pattern on the object; and

processing the image so as to derive a three-dimensional (3D) map of the object responsively to the transition of the diffraction pattern.

6. The method according to claim 5 , wherein directing the light comprises projecting multiple spots onto the object, wherein each spot exhibits the diffraction pattern responsively to a distance from the aperture of a respective location on the object onto which the spot is projected.

7. A method for mapping, comprising:

capturing an image of an object, which has a surface with features having respective shapes at respective locations on the surface, using an optical objective that is configured to modify the shapes of the features in the image as a function of a distance of the respective locations from the objective; and

processing the image so as to derive a three-dimensional (3D) map of the object responsively to the modified shapes of the features.

8. The method according to claim 7 , and comprising projecting a pattern of multiple spots onto the surface of the object, wherein the features in the image comprise the spots, and wherein processing the image comprises analyzing the shapes of the spots in the image.

9. The method according to claim 7 , wherein the optical objective comprises an astigmatic optical element having different, respective focal lengths in different meridional planes of the element.

10. The method according to claim 7 , wherein the objective comprises a diffractive optical element.

11. A method for mapping, comprising:

projecting a pattern having a size characteristic onto an object from an illumination assembly at a first distance from the object;

capturing an image of the pattern on the object using an image capture assembly at a second distance from the object, which is different from the first distance; and

processing the image so as to derive a three-dimensional (3D) map of the object responsively to the size characteristic of the pattern in the image and to a difference between the first and second distances.

12. The method according to claim 11 , wherein the projected pattern comprises multiple spots, and wherein the size characteristic is selected from a set of characteristics consisting of sizes of the spots and distances between the spots.

13. An apparatus for mapping, comprising:

an illumination assembly, which comprises an astigmatic optical element having different, respective focal lengths in different meridional planes of the element and is configured to project a pattern onto an object via the astigmatic optical element;

an image capture assembly, which is configured to capture an image of the pattern on the object; and

an image processor, which is configured to process the image so as to derive a three-dimensional (3D) map of the object based on features of the image that vary responsively to the different focal lengths.

14. The apparatus according to claim 13 , wherein the astigmatic optical element comprises a combination of at least two cylindrical lenses in different, respective orientations.

15. The apparatus according to claim 13 , wherein the astigmatic optical element comprises a diffractive optical element.

16. The apparatus according to claim 13 , wherein the astigmatic optical element comprises an off-axis element.

17. An apparatus for mapping, comprising:

an illumination assembly, which comprises an aperture and is configured to direct light via the aperture so as to project onto an object a diffraction pattern characterized by a transition from near-field to far-field diffraction;

an image capture assembly, which is configured to capture an image of the diffraction pattern on the object; and

an image processor, which is configured to process the image so as to derive a three-dimensional (3D) map of the object responsively to the transition of the diffraction pattern.

18. The apparatus according to claim 17 , wherein the illumination assembly is configured to project multiple spots onto the object, wherein each spot exhibits the diffraction pattern responsively to a distance from the aperture of a respective location on the object onto which the spot is projected.

19. An apparatus for mapping, comprising:

an image capture assembly, which is configured to capture an image of an object, which has a surface with features having respective shapes at respective locations on the surface, and comprises an optical objective that is configured to modify the shapes of the features in the image as a function of a distance of the respective locations from the objective; and

an image processor, which is configured to process the image so as to derive a three-dimensional (3D) map of the object responsively to the modified shapes of the features.

20. The apparatus according to claim 19 , and comprising an illumination assembly, which is configured to project a pattern of multiple spots onto the surface of the object, wherein the features in the image comprise the spots, and wherein the image processor is configured to derive the 3D map responsively to the shapes of the spots in the image.

21. The apparatus according to claim 19 , wherein the optical objective comprises an astigmatic optical element having different, respective focal lengths in different meridional planes of the element.

22. The apparatus according to claim 19 , wherein the optical objective comprises a diffractive optical element.

23. An apparatus for mapping, comprising:

an illumination assembly, which is located at a first distance from an object and is configured to project a pattern having a size characteristic onto the object;

an image capture assembly, which is located at a second distance from the object, which is different from the first distance, and is configured to capture an image of the pattern on the object; and

an image processor, which is configured to process the image so as to derive a three-dimensional (3D) map of the object responsively to the size characteristic of the patter in the image and to a difference between the first and second distances.

24. The apparatus according to claim 23 , wherein the projected pattern comprises multiple spots, and wherein the size characteristic is selected from a set of characteristics consisting of sizes of the spots and distances between the spots.