EZ Sextant

The phone's camera is used to make sightings of the sun, moon, Venus, or Mars. The sighting results are plotted as running fixes on a latitude/longitude grid for easy navigation. Or use your sextant and take advantage of the built-in almanac and plotting tools.

Sighting accuracy depends on, but not limited to: camera field of view, camera resolution, lens distortion, calibration, and user skill. A camera with a field of view equal to ninety degrees is optimal. If your phone has multiple cameras, the one with field of view closest to ninety degrees is chosen.

A sighting is made by taking a picture of the celestial object and horizon and entering the height above the water. Celestial objects supported are the sun, moon, Venus, and Mars. The image is stamped using the phone's clock but can be overridden if in error. Then you tap on the sun and center the cursors using arrows. Next, tap on the horizon and center the horizon line. The sighting results are plotted as a line of position. Two or more sightings are combined into running fixes, i.e., the best estimate of your position. As with a sextant, objects should have altitudes greater than 20 degrees to reduce refraction errors.

A one-time calibration is required to achieve the best achievable sighting accuracy. This entails taking five to ten images and entering an accurate latitude and longitude when taking the picture. Accurate sources of latitude and longitude are the chartplotter or VHF radio. Phone GPS's are not accurate enough when out at sea. Images taken on the beach can also be used for calibration using Google Earth for latitude and longitude.