Reference image techniques for three-dimensional sensing

1. A method, comprising:

providing a device that projects a pattern;

capturing a reference image of the pattern using an image sensor by projecting the pattern onto a reference surface while at least a first part of the reference surface, containing a first portion of the pattern, is located at a first distance from the image sensor and while at least a second part of the reference surface, containing a second portion of the pattern, is located at a second distance, different from the first distance, from the image sensor, and combining the first and second portions of the pattern into the reference image;

registering the captured reference image in a frame of reference of the device;

storing the registered reference image in a memory associated with the device; and

generating a three-dimensional (3D) map of an object, different from the reference surface, after storing the registered reference image by projecting the pattern onto the object, capturing a test image of the pattern on the object, and measuring local transverse shifts of the pattern in the test image relative to the reference image that is stored in the memory.

2. The method according to claim 1 , wherein capturing the reference image comprises capturing a first image of the pattern projected onto the reference surface at the first distance using the image sensor, and capturing a second image of the pattern projected onto the reference surface at the second distance using the image sensor, and wherein registering the reference image comprises registering the first and second images to produce a registered reference image, and wherein storing the reference image comprises storing the registered reference image in the memory.

3. The method according to claim 1 , wherein projecting the pattern comprises projecting the pattern into a first field of view, and wherein the image sensor has a second field of view different from the first field of view.

4. The method according to claim 1 , wherein the reference surface is oriented with respect to the image sensor to have a first region of the reference surface at the first distance from the image sensor and to have a second region of the reference surface at the second distance, different from the first distance, from the image sensor.

5. The method according to claim 4 , wherein the reference surface is planar and is oriented non-orthogonally with respect to an optical axis of the image sensor.

6. The method according to claim 4 , wherein the reference surface is curved between the first distance and the second distance.

7. Apparatus, comprising:

a projection and imaging device comprising:

a projector that projects a pattern of radiation;

an image sensor that captures images of a field of view on which the pattern is projected; and

a memory, which is configured to store a reference image of the pattern,

wherein the device is configured to generate a three-dimensional (3D) map of an object, after storing the reference image in the memory, by projecting the pattern onto the object, capturing a test image of the pattern on the object, and measuring local transverse shifts of the pattern in the test image relative to the reference image that is stored in the memory; and

a system for generating the reference image, which comprises:

a reference surface, which is different from the object that is to be mapped and is configured to enable the projection and imaging device to project the pattern onto the reference surface while at least a first part of the reference surface, containing a first portion of the pattern, is located at a first distance from the image sensor and while at least a second part of the reference surface, containing a second portion of the pattern, is located at a second distance, different from the first distance, from the image sensor; and

a processor, which is configured to combine the first and second portions of the pattern into the reference image, to register the captured reference image in a frame of reference of the device, and to store the registered reference image in the memory of the device.

8. The apparatus according to claim 7 , wherein the projector is configured to project the pattern into a first field of view, and wherein the field of view of the image sensor is a second field of view different from the first field of view.

9. The apparatus according to claim 7 , wherein the reference surface is oriented with respect to the image sensor to have a first region of the reference surface at the first distance from the image sensor and to have a second region of the reference surface at the second distance, different from the first distance, from the image sensor.

10. The apparatus according to claim 9 , wherein the reference surface is planar and is oriented non-orthogonally with respect to an optical axis of the image sensor.

11. The apparatus according to claim 9 , wherein the reference surface is curved between the first distance and the second distance.