Systems and methods are disclosed for determining a navigational constraint for a portable device using an optical sensor. The navigational constraint may be used to supplement other navigational solutions or may be used independently. The optical sensor may capture a plurality of samples to be processed to determine the constraint. Determining the constraint may include any or all of determining a context for usage, distinguishing usage modes, estimating an orientation of the portable device, determining an absolute and/or relative elevation, determining a direction of motion and determining a speed of the portable device from the samples.