>From the latest electronic version of "NASA Tech Briefs": Solar compass finds north the old-fashioned way
By using a multiple-pinhole screen in front of a sensing array, plus image-processing algorithms, researchers at NASA's Jet Propulsion Lab have built a solar compass that determines the axis of rotation of the Earth and, thus, true north. It uses a MEMS (microelectromechanical-system) microscopic pinhole mask in front of a 512W512-pixel image-detector array. The array also includes a 10-bit A/D converter and other support circuitry. As the sun traverses the sky, the software processes the digitized image path to determine the sun's angle relative to the stationary array, thus discerning north. If the processing system also includes a clock, you can use it to fix a 3-D position. The researchers report that a 10-minute observation period yields accuracy to about 100, and a period of several hours hones accuracy to a fraction of a degree. -