This is a discussion on Compasses within the Related Gear & Equipment forums, part of the Defensive Carry Discussions category; MAP COMPASS AND GPS
USING THE UTM GRID
A GPS is a great navigation tool. Among others things it can tell where you are on ...
September 13th, 2007†08:45 PM
MAP COMPASS AND GPS
USING THE UTM GRID
A GPS is a great navigation tool. Among others things it can tell where you are on hearth which was the main concern for earlier navigators of the Spanish and Portuguese navies, until reliable navigation tools such as the sextant were invented.
Land navigation and exploration was also the province of the sextant; it was used in the jungles with an artificial horizon (a separate glass case containing mercury), and the star to drop down was the sun, as the readings were taken during the day as tree canopy made night reading almost impossible.
Today a small gadget called GPS can do the same for us in only a few minutes. The tool can give us our position on a map using Latitude and Longitude, UTM, military grid, or user grid.
It can do this during the day or night, with clouds or storm, best of all the GPS can fit even in a small pocket, the new units are more accurate than ever and can pin point your position with an accuracy of a few feet.
This position can be plot in a topographic map if you have a latitude/longitude ruler or even eyeballed, if the map is provided with a UTM grid or military grid.
Most new topographic maps now are provided with an UTM grid (Universal transverse Mercator) which is based on the metric system. In this system the latitude is measured in meters north or south of the Equator, and the longitude from meters from the center of a zone, of course the names change and the longitude is called Eastings and the latitude Northings.
In our map you can see an X named start and another X named finish. The place marked finish is where we left the quads on the side of the trail to climb up to Blenheim Hill early that morning. The purpose was to check the creek for trout and scout the area adjacent to the top of the hill.
The reading on the GPS for the place where we left the quads, was 4.700.200 meters North (you use the margin of the map scale) and 541,100 meters East from zone 18 (you use the scale in the top of the map). The first two numbers are the Zone and do not count as meters.
As we had spent two days using the GPS on others locations the gadget was getting very low on battery juice, so we decided to navigate by compass and save the batteries to take readings of the position of interesting places only.
By the end of the day and very tired we found ourselves near the unimproved road that lead to the road next to the cemetery. A reading of our position with the GPS using the UTM system indicated that we were 4,700.000 meters north of the Equator and 539,400 meters east of the zone 18, (see how easy is to count meters in the 1,000 squares with the tickís marks in the margin of the map counting for 100 meters each).
Tracing a line from start to finish and measuring the degrees with the compass (used as a protractor and disregarding the magnetic needle) gave us a direction to go 80 degrees and 1700 meters for distance, (but the GPS already told us that).
The trek was on okay -terrain slopping downhill and we had to be careful with our footing only in the last 350 meters downhill to the quads.
The other option was to take the road going to the one near the cemetery (1300 meters) walk on that road passing by the ruins of the School until the next trail left (1900 meters) and walk uphill about 1,000 meter to the quads, a total of 4,200 meters.
In a heavy forest with no landmarks and not elevation to take triangulations readings with a compass, it is impossible to know where you are, the GPS can give you your exact position day or night and you can plot that position in the map using the Universal Transverse Mercator grid.
You can do that also with the Longitude and Latitude, but you have to prepare your map (with a different grid) and have a latitude and longitude ruler to measure your position. As GPSís are easily adjusted for the UTM grid, it is the most convenient and easiest to use of all the grids.
In this explanation we have used the three tools to complement each other, the map, GPS and compass, and demonstrated that finding a road at the end of the day, it is not the shortest route for traveling to your destination; it also demonstrated that you donít have to be glued to your GPS (as I see many people in the woods doing) to get your money worth out of the gadget.
September 13th, 2007†09:36 PM
I became a forward observer before the introduction of all the electronic gadgets they were using before I got out of the Army. So I can still relate to using the old compass and topo map for finding my way if need be.
When I got out of active duty and into the NGaurd it was very interesting to see the lack of map reading knowledge, even by the officers. I made it a point to make many corrections to their instructions when the goofed up.
I now use a gps, but haven't forgotten the old system.
Anyway good post and for those that keep shtf bags, a good compass would be something to think about.
Just remember that shot placement is much more important with what you carry than how big a bang you get with each trigger pull.www.ddchl.com
Texas CHL Instructor
Texas Hunter Education Instructor
September 13th, 2007†09:49 PM
For me it's just a weight/convenience issue. They're not exactly light, they use batteries (which can and do die). When the batteries die (IF you use the thing a lot) you have to replace them. If you're out on a multiday hike in rough terrain, you really don't want the added weight of extra batteries (even just 2AA's). So for me it's more of a negative convenience issue. I don't doubt their usefulness. I have one. Just dont typically take it if I'm out hiking anymore. In my little fantasy world...less is more.
September 20th, 2007†08:03 AM
AREA, LINE, AND POINT POSITION
In my previous post I marked my point position and the point position of the quads on the map with the help of the GPS and the UTM grid on the map.
That pin point of location is called point position, and should be the goal of every traveler in the wilderness to know about his point position; after all you could be lying down with a broken leg unable to move and in need of rescue.
Line position is when you know that you are on a feature on the map but cannot pin point your exact location, letís say you know you are somewhere along the river, road, ridge, trail or compass bearing, but you donít know exactly where.
Area position is when you know you are in a general area on the map; your goal should be to know at all times where you are on the map, and if you can tell your point position the better, you never know when you may need to summons help (over your cell phone or radio) and need to tell them exactly where you are.
Now we are going to try to mark our point position with the help of our compass and map alone, no GPS this time to help us out.
To accomplish this you need a map with an UTM grid. Since 1989 all new maps are printed with the UTM grid. If your map doesnít have it you can trace it by the ticksí marks on the edges of map using a yard stick and a pencil.
For compass and map work I recommend you spend a few dollars more and buy one with the adjustable declination scale, I use the Suunto M-5SK (smoke killer) but there are others in the market that have this convenient feature.
That way, when you are taking or plotting readings from the compass the values will be in geographic North and you will not have to be doing mathematics factoring the declination on your calculations.
Also forget about using lensatic or prismatic compasses, its readings are in magnetic and donít have a base plate that can be used as a protractor like in the Silva system. To use lensatic and prismatic compasses with maps you will also need to carry a protractor to measure the angles and convert the magnetic readings to true North by adding or subtracting the declination, something that you donít want to do when you are under pressure or confused by cold or stress.
The Silva system is a compass, protractor, measuring device, ruler, straight- edge and even (as in the case of the M-5SK and others) a magnifying glass.
If you rather use the compass that you already have, and it is a base plate compass or one with transparent base, you can mark your declination with a piece of white label like the one in this picture.
Just remember to place the compass magnetic needle in top of that mark to compensate for the declination.
It will be good if before entering the woods you can count with a base line; the base line could be the road where you left your car, a river, a power line or any other feature that is marked on the map and goes for a long way, that way you always have the option of trying to reach your base line if you are running out of daylight.
USE HANDRAILS IF YOU CAN
A handrail is a feature that is marked on the map. A trail, river, or other geographic feature that goes in the direction you want to go. When you are in a handrail, you are in a line of position. If you know you are on the trail or next to the creek, to find your point position you just need another feature that is on the map from where you can take a compass back bearing in the field.
Letís say you see a hill in the distance that is also marked on the map. Take a back bearing with your compass to that hill, you know how to do that, you point the compass direction of travel arrow to the hill and rotate the capsule until the SOUTH END of the magnetic needle is ďboxedĒ in the declination arrow.
Yes, for a back bearing use the SOUTH end of the magnetic needle, not the NORTH end.
Read the degrees at the junction of the bezel and line of travel arrow, and plot that in your map.
HOW TO PLOT
Letís say that the back bearing you took to the hill is 80 degrees, donít move the compass capsule to change that reading, place the long edge of the base plate of the compass on the hill that is on the map, and the direction of travel arrow toward your position (the river in this case), make sure the NORTH on the compass is toward the top of the map and then rotate the entire compass (not the capsule) until the North lines scribed in the base plate are parallel with the NORTH lines on the grid of the map.
For map work, always disregard the magnetic needle, you are using your compass as a protractor and measuring angles.
A line traced at the edge of the compass from the hill toward the river, will cross the river at the exact point where you are located, this is your point position. And now you can even read the coordinates of that position from the UTM grid, and tell any rescue party the UTM values of where you are.
This you will have to do when you know only that you are in a general area of your map, your area position.
To get your point position you need two features that are shown in the map from where you can take back bearing in the field. Letís say you are lucky and you see two hills that are also in the map and at more or less right angles. Take a back bearing on one and plot it in the map, now you are in a line of position, you are somewhere along that line. Take a back bearing on the other hill and plot it in the map, where the two lines cross, there is your point position.
Triangulation works even better when you use three features to take back bearings.
If you are in a featureless area with no hills, radio towers, power lines or other help for your triangulation, at least you should have been smart enough to look at your map often and noticed the changes in the topography.
You must know if you passed the hills that are in your map and how long ago, you must know if you are in a flat area and nearing an elevation change in the terrain or if the terrain starts to slope downhill. Based on these clues you will have an idea of what your area position is. With luck the chopper will look for you only in a reduced area of one kilometer based on the coordinates from the UTM grid that you will transmit over the phone or radio.
POINT POSITION AGAIN
Letís give here one example of point position using a real map, and a figured scenario so you understand how important point position is even if you are not interested in marking your tree stand on the map.
Letís say I am exploring the top of B-----g Ridge in the Adirondacks, this is a ridge that encompasses many miles and even knowing I was there, I didnít know where I was exactly.
To the West I can see the peak of S--d Pont Mountain, one of the tallest in the area.
Presently, I spotted in the forest floor something flashing in the sunshine and in picking that up; I held in my hands a pair of prescription eye glasses.
In further looking around I discovered a human skeleton dressed in the remains of orange hunting clothes. A rusty rifle near by confirmed my assessment that the unfortunate bones belonged to a hunter.
Looking at the back of his jacket remains I found a license tag protected by a transparent license holder, as the tags are made of weather and tear resistant material they have survived quite well the estimate three or four years of exposure to the elements.
In my pack I had some orange surveyor tape and I marked the area with it, then I took out my compass and took a back bearing to the top of S--d Pond Mountain, the back bearing is taken with the SOUTH part of the needle because you want the bearing FROM the mountain to your position. You can also take a direct bearing but then when plotting it in the map the direction of travel arrow should be pointing to the MOUNTAIN instead of from the Mountain to your position.
I like to do the back bearing, because if I were using a regular protractor the numbers to my position will be the back bearing numbers.
The back bearing indicates a 95 degrees direction from the top of the mountain, so I placed the compass with one long edge on the peak of the Mountain, and the direction of travel arrow toward the B----g Ridge, making sure that the NORTH part of the compass points toward the NORTH part of the map.
I rotated the whole compass by the base plate (I donít touch the capsule or change the setting in the bezel) until the lines inscribed in the base of the capsule are parallel to the North lines on the map.
Now the edge of the base-plate is passing over my exact position on the Ridge. I traced a pen line to connect the two points, and placed an X in the map to mark my discovery.
As I had to be back in New York City next morning for a court hearing, it is no way I was going to be bringing a party here to the top of the ridge, or getting further involved in this matter, so late that afternoon on my way back to New York I dropped an envelope in the police headquarters with a note of explanation, the marked map and the hunting tags of the corpse.
By the UTM grid they can get the exact location in Easterns and Northings and transfer that to a GPS equipped chopper and effectuate the recovery as well, or better, that if I were there to direct them.
October 17th, 2007†07:13 AM
This will be of interest only to the people that travel to locations around the world, and are in need of using a compass to get their bearings.
I first encountered compass dip, many years ago, in a trip to Bariloche, Argentina. I was there to fly-fish for trout in the Nahuel Huapi Lake and climb the Cerros Tronador, Catedral and Lopez.
I took my regular base plate compass, which I had used extensively in North America, and I found there that the needle was sticking to the card providing false readings.
I was baffled until my guide explained that most climbers from the states had compasses that stick and that I needed a compass with the needle balanced for the area. In my compass, the pull from the forces of the magnetic north made the south end of the needle dip and stick to the card.
I found later that when compasses are made, they are balanced for the zone that they are going to be sold, and that the manufacturers have indentified 5 zones of dip.
MAP OF THE FIVE ZONES
Compasses sold in North America are adjusted for the zone one, and where I was in Argentina was considered zone four. Compasses sold over there by the sporting good stores where adjusted for that zone.
If you have opportunity to travel to Australia, you will be in zone five and the dip of the needle will be even more pronounced.
ENTER THE GLOBAL NEEDLE
Suunto has come out with a couple of travelerís compasses with a global needle. Brunton has at least one in their line and maybe other manufacturers are doing the same.
This is a needle that is optimized to be use in all places (that is why they are called Global compasses). Brunton is making the 8096 AR (a racing compass) with the global needle, and it makes sense as the runners donít have to stop and level the compass perfectly to take readings as the global needle can work with even a 20 degree tilt.
Climbers can benefit from a global needle as they have more latitude to take a reading from a peak that is too close, as sometimes bearings have to be taken using the imaginary center line of a mountain instead of a peak when using the regular compasses, as the tilt upward will ground the regular needle. With the global needle the chances that you can still use the peak for your target are increased if the angle is less than 20 degrees.
So we should welcome the development of the Global needle and hope that more choices will be made available in the different models of compasses.
All the best
October 17th, 2007†07:42 AM
October 17th, 2007†05:25 PM
Great info. Motivates me to dig out my compass and practice before the November deer season.
October 19th, 2007†12:01 AM
As a professional surveyor a bit up in the years, I began with compasses and progressed to GPS. I want to tell you it is like comparing oranges to basketballs. GPS equipment is extremely reliable and almost always provides the data you need to find your way. Compasses have never been reliable - any little magnetic variable makes them suspect, whether it comes from the iron in the earth or the sunglasses worn by the user. You have to be extremely skilled with a compass to do as well as an unskilled person with a gps.
If compasses worked beter than gps receivers they would be very popular with the military. They aren't. The military uses gps.
As far as gps inadequacies, the only real issue is battery depletion. Carry backup batteries. Thats it.
November 1st, 2007†07:08 PM
"EVERYONE is operating with only partial information" :hand27:
Some Wise Guy, USA 2001
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