Multipath resolution of ToF signals
Techniques are described herein for determining whether multipath reflections are present in a sensed signal associated with a time-of-flight sensor. In various examples, multiple signals may be generated associated with differing wavelengths and exposure times. Such signals may be used to reference a map of values generated from, in some examples, simulations of environments in which multipath reflections are likely. The map, in turn, may provide one or more values associated with one or more distances associated with an object and a multipath reflection. Additionally, an emitted waveform may form the basis of a reference signal for demodulation of the plurality of signals to account for manufacturing, thermal, and other defects. The resultant distances may be used to filter data and remove “bad” pixels to form a resultant depth-image which may be used, for example, to control a vehicle.
1 . A system comprising:
an indirect Time-of-Flight, iToF, sensor system; and
a processing device configured to:
receive a first signal corresponding to a time-of-flight measurement at a first frequency;
receive a second signal corresponding to an additional time-of-flight measurement at a second frequency, different from the first frequency;
determine, based at least in part on the first and second signals, whether multipath reflections are present in an environment;
determine, by performing a lookup of a table and based at least in part on determining the presence of multipath reflections and the first and second signals, both a distance to a first object in the environment and a distance to a second object in the environment, the table relating a combination of the first signal and second signal to a set of distances comprising the distance to the first object and the distance to the second object; and
generate a signal indicative of the first and second distances.
2 . The system of claim 1 , wherein the processing device is further configured to:
receive first and second reference signals corresponding to the first and second signals; and
perform, based at least in part on the first and second reference signals and one or more of the first or second signals, a demodulation,
wherein performing the lookup is further based at least in part on the demodulation.
3 . The system of claim 1 , wherein the processing device is further configured to:
receive an additional signal associated with a first exposure and the second frequency; and
determine, based on the additional signal, an estimated distance,
wherein determining the first and second distances are further based at least in part on the estimated distance.
4 . The system of claim 1 , wherein the table is generated based at least in part on:
executing a set of simulations comprising a first simulated object and a second simulated object at a plurality of relative distances to a simulated time-of-flight sensor;
determining, based at least in part on the set of simulations, a plurality of values associated with simulated reflections off of the first and second simulated objects; and
storing, as the table, a map associating the plurality of values with the plurality of distances.
5 . The system of claim 4 , wherein the set of simulations are performed using waveforms that are predetermined from measurements on the first and second signals.
6 . The system of claim 1 , wherein the processing device is further configured to:
perform, based at least in part on the lookup, a filtering operation to generate filtered data; and
generate a depth map based on the filtered data.
7 . The system of claim 6 , wherein the processing device is further configured to control a vehicle based at least in part on the depth map.
8 . The system of claim 1 , wherein elements of the table represent a mapping of data, indicative of third and fourth signals having waveforms corresponding to waveforms of the first and second signals, to distances and reflectivities of objects in an environment, the waveforms of the first and second signals having been measured by observing actual emissions of the time-of-flight sensor.
9 . The system of claim 1 , wherein the processing device is further configured to:
receive third data indicative of a third signal at a third frequency different from the first and second frequencies, the third signal corresponding to a time-of-flight measurement representing a third reflection off the scene; and
further determine, by performing a lookup of the table and based on the first, second and third data, a distance to a third object in the scene and a third intensity of the first, second and third signals from the third object.
10 . One or more non-transitory computer-readable media storing instructions executable by one or more processors, wherein the instructions, when executed, cause the one or more processors to perform operations comprising:
receive a first signal corresponding to a time-of-flight measurement at a first frequency;
receive a second signal corresponding to an additional time-of-flight measurement at a second frequency, different from the first frequency;
determine, based at least in part on the first and second signals, whether multipath reflections are present in an environment;
determine, by performing a lookup of a table and based at least in part on determining the presence of multipath reflections and the first and second signals, both a distance to a first object in the scene and a distance to a second object in the environment, the table relating a combination of the first signal and the second signal to a set of distances comprising the distance to the first object and the distance to the second object; and
generate a signal indicative of the first and second distances.
11 . The one or more non-transitory computer-readable media of claim 10 , wherein the instructions further cause the one or more processors to:
receive first and second reference signals corresponding to the first and second signals; and
perform, based at least in part on the first and second reference signals and one or more of the first or second signals, a demodulation,
wherein performing the lookup is further based at least in part on the demodulation.
12 . The one or more non-transitory computer-readable media of claim 10 , wherein the instructions further cause the one or more processors to:
receive an additional signal associated with a first exposure and the second frequency; and
determine, based on the additional signal, an estimated distance, wherein determining the first and second distances are further based at least in part on the estimated distance.
13 . The one or more non-transitory computer-readable media of claim 10 , wherein the lookup table is generated based at least in part on:
executing a set of simulations comprising a first simulated object and a second simulated object at a plurality of relative distances to a simulated time-of-flight sensor;
determining, based at least in part on the set of simulations, a plurality of values associated with simulated reflections off of the first and second simulated objects; and
storing, as the table, a map associating the plurality of values with the plurality of distances.
14 . The one or more non-transitory computer-readable media of claim 13 , wherein the set of simulations are performed using waveforms that are predetermined from measurements on the first and second signals.
15 . The one or more non-transitory computer-readable media of claim 10 , wherein the instructions further cause the one or more processors to:
perform, based at least in part on the lookup, a filtering operation to generate filtered data; and
generate a depth map based on the filtered data.
16 . The one or more non-transitory computer-readable media of claim 15 , wherein the instructions further cause the one or more processors to control a vehicle based at least in part on the depth map.