A process executes at an electronic system. The process identifies device characteristics of an imaging device that includes signal emitters and signal detectors. The process illuminates a field of view by signals from the signal emitters according to a modulation signal generated by the imaging device. At each of the signal detectors, the process obtains a response signal, and samples the response signals to form a response vector. The process obtains a lookup table corresponding to the modulation signal and the device characteristics. The field of view is partitioned into a 3-dimensional plurality of voxels, and the lookup table specifies, for each voxel, expected signals received by the signal detectors when the voxel is filled and the signal emitters illuminate the field of view according to the modulation signal. The process compares the response vector to the lookup table to determine which voxels are filled.