Backwards sundial finds true north better than magnet or GPS

[jwl]

DITCH the magnets, it’s the sun’s time to shine. An advanced solar compass can find true north from anywhere on the planet – or off.

We have used solar navigation to get around since ancient times, based on the principles of a sundial but in reverse. Sundials are aligned north and cast a shadow based on the position of the sun that tells you the time. “With our device, if you know the time, from the position of the sun you can obtain the direction of true north,” says Daniele Murra of the Italian National Agency for New Technologies, Energy and Sustainable Economic Development in Rome, whose team built the compass.

Existing solar compasses, based on 19th-century technology, aren’t very accurate. So the team turned to a digital camera fitted with a slit lens to measure the angle of the sun in the sky. By combining this with a GPS sensor that provides the location and time, the compass can calculate the relative positions of the sun and Earth, and tell you which way is north (Optics Letters, doi.org/6kr).

Why not just use GPS alone, or a magnetic compass? Despite being a tool many of us use to get around these days, a lone GPS doesn’t give your orientation, only your position – that’s why smartphones also have a magnetic compass sensor.

But magnetic compasses aren’t accurate at high latitudes or near large amounts of metal, says Murra, so civil engineers and other industrial users rely on expensive, multi-signal GPS sensors to accurately determine orientation. The new solar compass is accurate to a hundredth of a degree and only costs around €100 to build, he says.

It could even work on other worlds by substituting Earth’s astronomical parameters with those of the planet, and by substituting the GPS with an internal clock, the team says.

https://www.newscientist.com/article/mg ... ts-or-gps/

Paper: https://www.osapublishing.org/ol/abstra ... 40-15-3619

[Broomstick]

There's also the problem of magnetic declination - not something most folks deal with on a daily basis, but the angle between where the compass points north and where true north lies varies as you travel about the globe AND varies over time as well. The longer your trip the more important this becomes, which is why learning about it and how to account for it is part of pilot training ground school. The bottom line, though, is that finding true north with a magetic compass takes a bit of math AND requires you to either have a pretty good idea of where you are already or an instrument with which to make appropriate measurements besides the compass. I'm guessing it's also still part of training naval navigators as well, whether for big or little boats.

[madd0ct0r]

also part of hiking, since you need to correct the map's magnetic north for the current one depending on the age of the map.

[Sea Skimmer]

GPS needs two antennas to give direction, not two complete systems as the article seems to imply and that isn't very expensive, a quick check of Google shows multiple systems for sale in the 90-120 dollar range. That's the same or less then the claimed cost for this solar compass, and for actual production items, not a concept with lab hardware. Two antennas is slowly becoming a defacto standard simply because it provides a means of improved error correction and thus increased accuracy, without requiring the added computer hardware to enable differential GPS where available.

Neither GPS won't work at all in the far north or south, but this is irrelevant something like 99.9% of the world population and almost all of the land mass of the planet outside Antarctica. As I recall GPS Block III will have true global coverage, but that's still six or seven years away from being fully operational and keeps being delayed.

I think the original title of the print article sounds more accurate then the online title. It was according to the article itself 'Backwards sundial makes useful compass'. That's true. Useful it is in some contexts. But better? GPS will work inside lightly clad buildings, under dense trees, inside moving vehicles and in rain. A sun dial kind of falls flat on all of that.

[Broomstick]

Consider this:

Why do modern airliners, even the most up-to-date, continue to carry not only radionavigation equipment dating back to the WWII era, but also a magnetic compass?

Because every navigational system has weaknesses as well as strengths. When you're traveling without roadsigns (and that is the case with aviation) multiple back-ups for your ability to locate yourself can be a matter of life and death.

Before GPS and transoceanic beacon systems, airplanes would sometimes use starcharts and tools like a sextant to navigate across the Pacific at night.

Sure, this new-fangled sundial has limitations, but I find the notion of yet another way to navigate fascinating. If the Earth undergoes something like a magnetic pole reversal (which is has multiple times in the past) who knows? This might become more useful than a magnetic compass for awhile.

[Elheru Aran]

Don't Boy Scouts and such learn how to find north via shadows and such, a few different methods, anyway? Is this actually new?

[Broomstick]

And ancient Polynesian sailors navigated by things like ocean currents and bird flights - there are a LOT of ways to navigate.

[LaCroix]

Well yes, a magnetic compass is fine and a good backup, but this new sundial uses GPS in order to compute true north. (you need current time and position to use it)

So a GPS receiver with dual antennas still beats it. And where a GPS would fail, this sundial would, too. While the dual GPS would still work in most situations where that sundial would fail (Cloudy or other view obstruction).

So it's worse than a dual GPS, costs about the same, and less failsafe than a magnetic compass.

Nifty tool, but just for people who really need to have everything.

[Ziggy Stardust]

Don't Boy Scouts and such learn how to find north via shadows and such, a few different methods, anyway? Is this actually new?

These methods aren't exact, though. These are just to give yourself a relative idea of where North is for rough navigational purposes, primarily over small areas (<10 or 20 miles).

[jwl]

GPS needs two antennas to give direction, not two complete systems as the article seems to imply and that isn't very expensive, a quick check of Google shows multiple systems for sale in the 90-120 dollar range. That's the same or less then the claimed cost for this solar compass, and for actual production items, not a concept with lab hardware. Two antennas is slowly becoming a defacto standard simply because it provides a means of improved error correction and thus increased accuracy, without requiring the added computer hardware to enable differential GPS where available.

Neither GPS won't work at all in the far north or south, but this is irrelevant something like 99.9% of the world population and almost all of the land mass of the planet outside Antarctica. As I recall GPS Block III will have true global coverage, but that's still six or seven years away from being fully operational and keeps being delayed.

I think the original title of the print article sounds more accurate then the online title. It was according to the article itself 'Backwards sundial makes useful compass'. That's true. Useful it is in some contexts. But better? GPS will work inside lightly clad buildings, under dense trees, inside moving vehicles and in rain. A sun dial kind of falls flat on all of that.

I've had a look too now and these compasses seem to have an accuracy of ~0.3 degrees if stated, which is pretty different from the 0.01 degrees this sundial compass claims.

[The_Saint]

I also like the idea of being able to navigate on other planets where the magnetic field is either not reliable or not well mapped out. Assume a mars rover: it already has multiple cameras and some kind of reliable on-board clock, all you need to add is a microchip or two and some extra programming, bang the rover now has non-gps based navigation.