Geodetic surveying with time synchronization

1. Method implemented by a geodetic instrument for determining a direction to a geodetic target configured to identify itself by emitting an optical pulse, the method comprising:

capturing, using at least one imaging device arranged at the geodetic instrument, a first image and a second image of the geodetic target;

synchronizing the geodetic instrument with the geodetic target for capturing the first image concurrently with emission of the optical pulse by the geodetic target, and for capturing the second image nonconcurrently with emission of the optical pulse by the geodetic target;

obtaining a difference image between the first image and the second image; and

determining, based on a position of the optical pulse emitted by the geodetic target in the difference image, the direction to the geodetic target from the geodetic instrument,

wherein synchronizing the geodetic instrument with the geodetic target includes:

establishing a time reference common to the geodetic instrument and the geodetic target; and

obtaining information about allocation of a set of non-overlapping time slots comprising at least a first time slot and a second time slot,

wherein the first image and the second image are captured by the geodetic instrument within the first time slot and the second time slot, respectively.

2. The method of claim 1 , wherein the synchronizing includes receiving a signal indicative of a common event.

3. The method of claim 2 , wherein the signal indicative of the common event comprises at least one of an electromagnetic signal, an electric signal, a GNSS code, a single electric pulse, or a single electromagnetic pulse.

4. The method of claim 2 , wherein the signal indicative of the common event is received by the geodetic instrument from the geodetic target, wherein the signal indicative of the common event is sent to the geodetic target from the geodetic instrument, or wherein the signal indicative of the common event is received by the geodetic target and the geodetic instrument from an external device.

5. The method of claim 1 , wherein the first image and the second image are captured within a time interval corresponding to at most one frame readout time plus two times a frame exposure time of said at least one imaging device.

6. The method of claim 1 , wherein the first image is captured by a first imaging device and the second image is captured by a second imaging device.

7. The method of claim 1 , wherein the capturing of the first image and the second image is repeated to capture a plurality of first images and a plurality of second images in an interleaved fashion.

8. The method of claim 7 , wherein the plurality of first images are captured at a rate corresponding to a rate at which the geodetic target is configured to emit a plurality of subsequent optical pulses.

9. The method of claim 7 , wherein the plurality of first images and second images are captured at a combined rate corresponding to twice the rate at which the geodetic target is configured to emit the plurality of subsequent optical pulses.

10. The method of claim 9 , wherein a time interval between a first image and an immediately preceding second image is equal to a time interval between the first image and an immediately succeeding second image.

11. The method of claim 7 , wherein the plurality of first images and second images are captured at a combined rate corresponding to at least 60 Hz.

12. The method of claim 1 , wherein a frame exposure time of said at least one imaging device is shorter than or equal to a duration of the optical pulse emitted by the geodetic target.

13. The method of claim 1 , further comprising:

synchronizing the geodetic instrument with the geodetic target and a second geodetic target configured to identify itself by emitting an optical pulse for capturing the first image nonconcurrently with emission of the optical pulse by the second geodetic target.

14. The method of claim 1 , further comprising:

determining, based on the position of the optical pulse emitted by the geodetic target in the difference image, a position of the geodetic target relative to the geodetic instrument.

15. A geodetic instrument, comprising:

at least one imaging device configured to capture at least a first image and a second image of a geodetic target configured to identify itself by emitting an optical pulse, and

a processing unit, configured to:

synchronize the at least one imaging device to capture the first image concurrently with emission of the optical pulse by the geodetic target, and to capture the second image nonconcurrently with emission of the optical pulse by the geodetic target, by:

establishing a time reference common to the geodetic instrument and the geodetic target; and

obtaining information about allocation of a set of non-overlapping time slots comprising at least a first time slot and a second time slot,

wherein the first image and the second image are captured by the geodetic instrument within the first time slot and the second time slot, respectively;

receive, from the at least one imaging device, the first image and the second image;

obtain a difference image between the first image and the second image, and

determine, based on a position of the optical pulse emitted by the geodetic target in the difference image, a direction to the geodetic target from the geodetic instrument.

16. The geodetic instrument of claim 15 , further comprising a receiver configured to receive a signal indicative of a common event, wherein the processing unit is configured to synchronize the at least one imaging device based on the received signal indicative of the common event.

17. The geodetic instrument of claim 16 , wherein the receiver is a GNSS receiver.

18. A geodetic target configured to identify itself to a geodetic instrument by emitting at least one optical pulse, comprising:

an optical source configured to emit the at least one optical pulse, and

a processing unit configured to synchronize the optical source to emit the at least one optical pulse concurrently with a capturing of a first image by the geodetic instrument, and nonconcurrently with the capturing of a second image by the geodetic instrument, by:

establishing a time reference common to the geodetic instrument and the geodetic target; and

obtaining information about allocation of a set of non-overlapping time slots comprising at least a first time slot and a second time slot,

wherein the optical pulse is emitted by the geodetic target within the first time slot, and

wherein the first image and the second image are captured by the geodetic instrument within the first time slot and the second time slot, respectively.

19. The geodetic target of claim 18 , further comprising a receiver configured to receive a signal indicative of a common event, wherein the processing unit is configured to synchronize the optical source based on the received signal indicative of a common event.

20. The geodetic target of claim 19 , wherein the receiver is a GNSS receiver.