Finite-Aperture Limits for Yaw Estimation in Confocal Non-Line-of-Sight Imaging

Non-line-of-sight (NLOS) time-of-flight imaging can recover hidden-scene geometry from the transient image measured on a relay wall. While the finiteness of the relay wall is known to constrain reconstruction, its impact on the angular estimation of the target has not yet been characterized. We address this gap through two complementary analyses. First, we derive a simple geometric visibility criterion based on a vertical switch line on the wall, and identify the angular range over which the finite wall still preserves the main transient features needed for a unique planar reconstruction. Second, we quantify angular sensitivity through the Fisher information of the normalized transient shape, showing that yaw sensitivity is not distributed uniformly across the wall and decreases smoothly as the most informative part of the measurement is progressively clipped by the finite aperture. In this way, the switch-line threshold emerges as a geometric transition rather than a complete loss of angular information. Our findings help clarify the limits of angular estimation with finite relay walls and provide guidance for interpreting and designing confocal NLOS measurements.