Structured light is directed across a monitored region. An image is captured of a light pattern that forms on the object as a result of the object intersecting the structured light when the object is placed at a first position in the monitored region. A geometric characteristic is identified of the image of the light pattern. The geometric characteristic is variable with a depth of the first position relative to where the image is captured. The depth of the first position is approximated based on the measured geometric characteristic.