If you've ever read a map, you notice a series of numbers around the edges. This is the grid scale and digitizes the grid of the map to correspond to a spot on the groud. So, when you know the grid number of the spot on the ground, you can find it when looking at a map. Simple, no?
Actually, no. Complicated as hell. I was raised using the MGRS (Military Grid Recognition System) which our Army uses to find the way, to navigate. I learned the MGRS in 1973 and used it almost exclusively for 30 years.
Common civilian maps are marked in Latitude and Longitude, which is the standard worldwide for civil navigation. Ptolemy first used it in mapping in 150 A.D. The English changed it later, running the 0 meridian (the prime meridan) through London. Latitude and Longitude are mapped using degrees, minutes and seconds. The problem is that a round Earth doesn't translate well on a flat map. Everything is measured as being so many degrees east and west of London, and north or south of the equator. Ancient mariners have been using this system for years, and the practice has been passed to the present day. Like most navy systems, it's screwed up. The distances on a lat/lon map change when you get away from the equator.
One degree of latitude equals 60 nautical miles at the equator. When you get to either pole, all of the lines of longitude converge to a single point. You can cover them with your foot. That, children is a screwed up system. Yet, it's the system that is used by the majority of the world. I'll learn to use it, and be happy with it.
Last night, I was trying to give my buddy Junior, some coordinates to a deer camp. It is located, roughly, at 31 degrees, 41 minutes, 34 seconds North, 92 degrees, 12 minutes, 49 seconds West. Hopefully, you can see the map here.
We emailed back and forth trying to get the numbers to read into a particular mapping system. It seems that someone took the Lat/Lon system that everyone has been reading since Ptolemy and digitized it. The degree side is still intact, but the minute/second series of numbers has been digitized. We've managed to mix the two systems to make it totally unintuitive. This is totally screwed up. It is neither english, nor french. It is neither metric nor standard. It is probably nautical.
The problem is that we now have Global Positioning systems. Wander through any good sporting goods store and you'll see a selection based on features, ruggedness, and usage. We have these things in tanks, humvees, and your family car. Sportsmen carry them in their pockets. They use different mapping grids. It's confusing.
We need one standard, one grid, that covers the whole globe. Whatever it is, it should be universally adopted and used on all maps, all computer programs, all GPS devices. One system for the world. The power players in the mapping community need to get together and decide which system we are going to use, and relegate the other systems to the trash heap. If you need a name for it, call it the PawPaw system. That rolls off the tongue nicely, doesn't it?
What's wrong with the UTM coordinate system? Except I forgot how to use it. . . .
ReplyDeleteNot a bad explanation for someone who never went to Navigator School.
ReplyDeleteThe reason the GPS industry switched from degrees, minutes and seconds (and dits of a second) is that it requires some math to be able to think in a base-60 system.
The GPS units, however, can all be configured to do either the degrees-and-decimals system or the base-60. Just go into the set-up menu.
GPS is in everything now, and public safety outfits were the first to insist on the change, and when they did, everyone had to follow, because they have the big bucks for equipment, so the chips were programmed for them.
As a Master Navigator, the difference doesn't mean squat to me, except that it's easier to memorize a set of base-60 coordinates than a degree-deci set out to 5 to seven decimal places.
Same with UTM. The "right-left" and "up-down" grid system gives huge strings of numbers which are difficult to remember, dangerous to transpose and generally are a pain in the ass.
The Brits had some foresight.
BTW, the USAF developed a separate Grid system for flying that included a new compass rose. It had the advantage of equally-spaced grid squares anywhere on the globe, but it also required the compass to be constantly corrected with the grid deviation, which changed according to the "standard" latitude. We navigators looked on it as a huge burden when not flying in the polar regions, but when we did fly up (or down) near the poles, it was a godsend.
geez, even my 6 year old E-Trex can convert between decimal degrees; degrees, minutes and seconds; and UTM.
ReplyDeleteJust go in to setup and pick whatever system you want to use to enter data in. Then when you are done, you can switch it to whatever system you want to use the GPS with. It should convert everything without any extra effort.
If you don't want to do that, search the web for javascript converters. Try the one at jeEep.com:
http://jeeep.com/details/coord/
I prefer UTM when I have a good topo map and one of those clear plastic thingys that you probably used to call in airstrikes. If I read the GPS and know where I am, I can use the grid tool to find the coordinates of where I want to be. Since it's based on a grid of meters, I could just use Pythagoras' Theorem to find the proper distance, but I just usually let the GPS do that work.
Not every map has UTM tick marks, let's say it only has degrees and minutes shown. In this case I want degrees and decimal minutes instead of degrees, minutes and seconds, because there aren't any seconds ticks on my map and I think in base ten.
My dad built computers for bombers way back when computers meant tubes. For flying over the north pole, they has something called “polar coordinates”, where the whole north/south pole thingy would be turned 90 degrees.
Old Joke: That's the great thing about standards, there are so may to choose from.
A PRACTICAL GUIDE TO GPS - UTM
ReplyDeleteby Don Bartlett
http://www.dbartlett.com/
(we're playing with maps over on my blog this week. I've got one post up and material for at least one more)
That Don Bartlett GPS - UTM guide is written so convoluted as to be useless. Got a better one?
ReplyDeletej said...
ReplyDeleteThat Don Bartlett GPS - UTM guide is written so convoluted as to be useless. Got a better one?
hmm, sorry, this one is how I groked UTM. I first found it about 7 years ago, but I thought it was the best one out there.
If you didn't read that far, skip down to here: http://www.dbartlett.com/index.htm#utm
and I suppose you could always try wikipedia: http://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system
Oh, and if you like google maps, but wished it had a topographic option, try this. It looks like a nice spot for a camp, right next to a stream. I hope the bugs arn't bad.
Just found this:
ReplyDeletehttp://www.uwgb.edu/dutchs/FieldMethods/UTMSystem.htm