Navigation · 1:27pm Jul 25th, 2016
Getting lost is no fun. If you’re someone who has to be somewhere for something, it sucks even more.
At its most basic, finding your way around involves measuring distances from known places. That could be your starting location, ending location, or a landmark in between. It’s mostly trigonometry.
Many people on this site have a technical background, but let’s do a quick refresh.
Let’s say your house is at point A. You’re currently at x, and you want to go to point B. If you know the distance c from A to B, and you know what angle e that you are from A, you can figure out how far and what direction you should go to reach B.
If you have a map, you can look for landmarks that are visible from your position. By taking lines of bearing, you can see where the lines intersect and determine your position. You can find angles with a compass. You can use an astrolabe or a sextant to find angles to stuff in the distance, even stars.
Celestial navigation is generally only doable on clear nights, but can produce amazingly accurate locations. Even if you don’t know how to use an astrolabe or sextant, at the very least you owe it to yourself to learn a simple trick for finding direction.
The north star:
And for you southern hemisphere folks:
I could go into the complicated process of all the fancy manual methods, but in the interest of keeping this blog at the overview level, we’ll just say that it’s the 21st century and we have technology to help us.
But trig is still a big part of that. Global Positioning System (GPS) measures distances from satellites to determine your location. GLONASS (Russia’s version of GPS), GALILEO (European Union’s), and BeiDou (China’s) function the same way. In fact, many civilian devices such as smartphones use both GPS and GLONASS. GPS has an encrypted military mode that is more accurate than civilian mode. Presumably, the other systems do too.
Most location-finding devices will probably give you a latitude/longitude number. That tells you how many degrees you are from the reference point. The Prime Meridian is an arbitrary vertical line that runs from the North Pole to the South Pole though Greenwich, England. The place where the Prime Meridian meets Earth’s equator, off the coast of Africa, is the lat/long base - the 0,0 point.
Note: Time zones are based (mostly) on location. The day “begins” on the Prime Meridian: Greenwich Mean Time (GMT). Timing is important for many aspects of navigation. The US Naval Observatory uses an atomic clock to set official US time.
Latitude is the horizontal east/west direction from the reference. Longitude is the vertical north/south direction. You can remember that because the horizontal latitude lines get smaller near the poles, but the vertical longitude lines around the Earth are all equally long.
But of course coordinates can’t be that easy. They’re often defined as decimal: (e.g. 34.6368°N) or with minutes and seconds (e.g. 34°38'13"N). Be careful not to get them confused. The two examples given in this paragraph point to the same location, but are clearly not the same digits. A degree minute is 1/60 of a degree, and a second is (of course) 1/60 of a minute.
Try this at home: Want to work out distances in your head? The earth is about 25,000 miles in circumference and is divided into 360 degrees, so one degree of longitude is about seventy miles. At the equator, so is latitude. As the latitude lines get shorter, most places in the US are about fifty miles per one degree of latitude.
A nautical mile is defined as one minute of one degree of latitude. So… one degree of longitude is exactly sixty nautical miles.
Whew, things are only getting more complicated. Once you know where you are on the planet, how do you tell other people? Well, hopefully you’re using the same map. Remember how we talked about the distance from your home? Well, making a map has to start from somewhere. Two maps using different reference points could be different.
GPS, and many US systems, use a reference called World Geodetic System 1984 (WGS 84). It’s been updated a few times since ’84, but not massively overhauled. It doesn’t need to be, as it’s believed to be able to locate Earth's center of mass to an accuracy of less than 2 cm.
And if you try to use maps and locations provided by one reference meant for another, you might have a bad time. Even using maps with a different projection than intended could cause problems. Ships have been wrecked because of this stuff.
In an attempt to make this a little more standardized, NATO developed the Military Grid Reference System. It assigns a box to every part of the earth. Boxes come in different sizes, and the more characters in the box’s name, the smaller and more precise it is.
4QFJ16 describes a box 10km in size.
4QFJ123678 is 100m big.
4QFJ1234567890 is down to 1m. (Which happens to be a spot on the taxiway at the Honolulu airport, if you care.)
The area in question. The smallest boxes shown here are 10km, so you can see where 4QFJ16 is.
No, MGRS doesn’t really make things easier, but at least everyone is working on the same page. And with technology, you put in the grid number and it tells you where that is.
You may have noticed that the earth is round. How do you lay square grids on a spherical planet? Here’s the MGRS map of the north pole:
Fortunately, the average civilian doesn't have to deal with this. Navigation is very important to our daily lives, so smart people have taken a lot of time to make it as easy as possible. Think about that the next time your GPS can’t find you.
Lost?
Yeah, a complicated topic that wasn't really made much easier. You can take an entire semester on one facet of navigation and not learn it all. I just wanted to post this so I had a reference for MGRS. That'll be important in another blog I do soon.
4111811
Learning how to navigate is easy, learning why and how it works take a crapton of time
I've got a decent warm and fuzzy on quite a bit of it. I'm pretty sure I'm Hurley for the rest of it.
Wow, this blog was a lot more complicated than I thought it would be, I didn't know anything about MGRS.
Mind if some comments here related to Nav stories?
I'll start off by giving a shout out to 217 ACU's Lcpl. 'B' for leading a 211 section 2K off course and into a minefield.
4113576 I mean, I studied orienteering in Boy Scouts, but I never did that.