Ahoy, GPS-stranded motorist. Stop banging the dashboard, and consider this timely reincarnation of dead reckoning to help you find your way out of "GPS-denied environments," or at least alert others to where you can be found.

Seer Technology is offering a miniature, self-contained, electronic navigation unit called NaviSeer that mixes GPS and DR in a complex gumbo of hardware and proprietary algorithms to deliver user location in real time.

It does this by blending the output from three gyros, three accelerometers (one at each axis,) a magnetometer, and a baro altimeter, and then running it through a Kalman filter.

The result: coordinates accurate to within less than a yard, according to Seer. And no, it "does not require sensors to be worn on the legs or feet."

"The NaviSeer product fills a giant void in the market for personal navigation products," said Fred Gallander, CEO of Seer. "We are seeing tremendous interest in this product from Fire, Police, SWAT, and military applications, where lives are in danger if personnel are "off the radar screen," inside buildings or other GPS-denied areas."

DR is a tried-and-true method for keeping track of where you are, using a fix (starting point), course, speed, and time traveled; it's how old-timey mariners navigated when they couldn't see the stars. It's also how ants find their way home. A Kalman filter is a powerful set of mathematical equations, which, when fed a sequence of observations, can provide a flow of estimates on past, present, and even future positions.

NaviSeer uses GPS to continually update its DR function, which, in turn, stands ready to take over, should GPS be denied. When that happens, "motion classification algorithms analyze movement and compensate when the user is moving backward, sideways, running, crawling, or just moving in place," according to Seer.

An "automatic compass orientation algorithm" gives the azimuth when the user is upright or prone. The result is a continuously updated feed of digital latitude, longitude, and elevation positions triggered by body movement.

If that doesn't work, there's always the stick-and-shadow method.