To date, the existing sundials and solar compasses use a gnomon, such as a stylet, to project a shadow under the sun on a marked surface to find the time or the
true north. Because of the fussiness of the shadow and the dependence of the
position of the sun with the day of the year (equation of time), the accuracy is low. The present invention discloses an omni-directional lens, which can focus the sun beam into a sharp spot with a long
depth of field. By projecting the spot on a cylindrical panel, both the day of the year and the time of the day can be read off simultaneously with very high accuracy. Because of the simultaneous displaying of time and date, no equation-of-time correction is required. If the time is known, the
true north can be determined with high accuracy, and the device becomes a reliable and easy-to-use solar
compass.4,384,408Bohlayer19834,520,572Spilhaus19854,835,875Fuller19894,945,644Fuller19905,197,199Shrader19935,425,178Steele19956,301,793Gottesman20016,604,290Gottesman20037,114,262Andrewes20069,428Burt18364,899.451Dandurand19905,425,178Steele19955,459,931Waltho1995