System and method for field calibrating video and lidar subsystems using independent measurements
A system uses range and Doppler velocity measurements from a lidar subsystem and images from a video subsystem to estimate a six degree-of-freedom trajectory of a target. The video subsystem and the lidar subsystem may be aligned with one another, and hence calibrated, by determining, for example, a centroid of an iris determined from the lidar subsystem and a centroid of the iris determined from the video subsystem and determining a calibration offset between the two centroids.
1. A method for calibrating a lidar subsystem with a video subsystem, the method comprising:
receiving a plurality of measurements generated by the lidar subsystem, each of the plurality of measurements corresponding to a location of a point on a target and an amplitude of a return signal from the point on the target;
receiving at least one image of the target generated by the video subsystem;
determining a lidar location of an iris of the target based on a low intensity amplitude of the return signal of at least some of the plurality of measurements;
determining a video location of the iris of the target based on the image of the target;
determining a calibration offset between the lidar subsystem and the video subsystem as the difference between the lidar location of the iris and the video location of the iris; and
calibrating the lidar subsystem with the video subsystem based on the calibration offset.
2. The method of claim 1 , wherein a location of the point on the target comprises an azimuth, an elevation, and a range.
3. The method of claim 2 , wherein the location of the point on the target further comprises a Doppler velocity.
4. The method of claim 1 , wherein determining a lidar location of an iris of the target based on the amplitude of the return signal of at least some of the plurality of measurements comprises:
determining which of the plurality of measurements have a low amplitude of the return signal relative to other of the plurality of measurements.
5. The method of claim 4 , wherein determining a lidar location of an iris of the target based on the amplitude of the return signal of at least some of the plurality of measurements further comprises:
for those of the plurality of measurements that have the low amplitude of the return signal, determining the lidar location as a centroid location of the respective locations of those of the plurality of measurements.
6. The method of claim 1 , wherein determining a video location of the iris of the target based on the image of the target comprises:
determining an iris contour of the iris of the target based on the image of the target.
7. The method of claim 6 , wherein determining the video location of the iris of the target based on the image of the target further comprises:
determining the video location as a centroid location of the iris contour.
8. The method of claim 1 , wherein determining a video location of the iris of the target based on the image of the target comprises:
performing Fraunhofer processing on the image of the target to identify the video location as a centroid location of the iris of the target.
9. A system for calibrating a lidar subsystem with a video subsystem, the system comprising:
a lidar subsystem configured to generate a plurality of measurements, each of the plurality of measurements comprising a location of a point on a target and an amplitude of a return signal from the point on the target;
a video subsystem configured to provide an image of the target; and
a processor configured to: receive the plurality of measurements from the lidar subsystem, receive the at least one image of the target from the video subsystem, determine a lidar location of an iris of the target based on a low intensity amplitude of the return signal of at least some of the plurality of measurements, determine a video location of the iris of the target based on the image of the target, determine a calibration offset between lidar subsystem and the video subsystem as the difference between the lidar location of the iris and the video location of the iris, calibrate the lidar subsystem with the video subsystem based on the calibration offset.
10. The system of claim 9 , wherein a location of a point on a target comprises an azimuth, an elevation, and a range.
11. The system of claim 10 , wherein the location of the point on the target further comprises a Doppler velocity.
12. The system of claim 9 , wherein the determine a lidar location of an iris of the target based on the amplitude of the return signal of at least some of the plurality of measurements comprises:
determine which of the plurality of measurements have a low amplitude relative to other of the plurality of measurements.
13. The system of claim 12 , wherein the determine a lidar location of an iris of the target based on the amplitude of the return signal of at least some of the plurality of measurements further comprises:
for those of the plurality of measurements that have the low amplitude, determine the lidar location as a centroid location of the respective locations of those of the plurality of measurements.
14. The system of claim 9 , wherein determine a video location of the iris of the target based on the image of the target comprises:
determine an iris contour of the iris of the target based on the image of the target.
15. The system of claim 14 , wherein determine the video location of the iris of the target based on the image of the target further comprises:
determine the video location as a centroid location of the iris contour.
16. The system of claim 9 , wherein determine a video location of the iris of the target based on the image of the target comprises:
perform Fraunhofer processing on the image of the target to identify the video location as a centroid location of the iris of the target.