Camera-Based Parkinson Gait Assessment in Ordinary Home Spaces: Geometry, Task Validity and Patient Equipment Burden

Abstract Ordinary smartphone cameras could reduce the equipment and travel requirements of gait assessment, but inexpensive image acquisition does not guarantee valid measurement or affordable completed care. This methods perspective examines the geometric and practical conditions under which home video could support Parkinson assessment. A targeted narrative selection includes recent Parkinson video studies, markerless validation, camera calibration and clinical measurement methods. Two original deterministic analyses quantify errors that can arise before a predictive model is applied. Under a simplified projection model, a calibration plane at three metres combined with movement at 3.3 metres produces a 9.1% underestimate of a spatial length; adding a 20-degree departure from the image plane increases the underestimate to 14.6%. A separate timing analysis shows that nearest-frame localization of two events can produce an interval error bounded by one frame under idealized assumptions, equivalent to 33.3 milliseconds at 30 frames per second. These examples are hypothetical measurement calculations, not observed device performance. The proposed framework distinguishes pose detection, spatial calibration, event timing, task validity and clinical interpretation. It treats limited space, occlusion, assistance and failed recordings as features of the intended population rather than reasons to exclude inconvenient participants. Patient affordability is assessed through equipment requirements, direct charges, repeat attempts and necessary follow-up, while provider resources inform sustainable financing. Recent camera studies justify further evaluation but do not establish unrestricted home validity. 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