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How do you "follow a bearing"?


lackdog

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The subject of this is my question. I have cam across caches that require I follow a bearing and I;m not 100% clear on this. I know it means turn and walk a certain direction, but im still confused. for instance:

 

"Get out of your car and go about 120 yards heading approximately 275 degrees."

 

or

 

"306 degree bearing - follow this about 36 paces to the cache."

 

Any help on explaining this is appreciated

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On a compass the degrees all the way around add up to 360. So if you have a compass and it shows the #s on it (180, 240, 360, 60, etc) you can figure out which direction you should be going.

Make your needle and the North line up, then figure out from the compass which direction 270 is, and walk that way.

I think I may have explained it more confusing than it actually is, but I can't think of any other way to explain it.

-Jennifer

 

Nothing is really work unless you would rather be doing something else. (JM Barrie)

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0 degrees is north, 90 is east, 180 is south, and 270 is west.

 

To be accurate, you'd need a compass. Use the compass to find the desired bearing, pick an object/point in that direction, and head toward it. I'm new to compasses, so I'm sure someone here can give better instruction.

 

You can also use your GPSr's "Project" feature. I believe they all have it; I hear a lot of people wonder why it's even there. This is how the yellow eTrex does it: First, mark a waypoint where you're standing. Then select this point and choose the "Project" option. Enter the bearing and distance, and viola, a new waypoint to Go to.

 

Now, the yellow eTrex only allows distances in increments of 1/10 of a mile or km. If your desired distance is less than that, as in your examples, you can still use Project to give you the correct direction, but you'll have to make the point further out and estimate the distance yourself as you walk.

 

I'll step aside and let someone else discuss magnetic and true north. I'm not touching that.

 

migo_sig_logo.jpg

vlip2.gif Now cache away, cache away, cache away all!

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OK, get out of the car and move a short distance away from it. (The metal will cause an error in the compass reading.) A bearing is simply the direction from point A (car) to point B (cache). To determine the bearing, stand with the compass level and the index line (the arrow printed on the bezel) aligned with the north pointer. The arrow, the north/south needle, and you are now pointing north. Now, rotate your body until the number “275” is aligned with the index line. The numbers will rotate as you do because the compass needle will keep pointing north. You just stop rotating when the bearing you want to travel in is aligned with the index arrow on the compass bezel. Now, look straight in the direction you and the index line are facing and pick out a tree or something – then walk to it. Count off the paces and that should get you in the area. If there’s no tree or other landmark to aim yourself at, just glance at the compass now and then to make sure you’re heading in the right direction.

 

275 degrees is only five off from due west. You could also just aim yourself at the setting sun and pace it off. That will get you in the area of the cache at least as good as the average set of coordinates. But, the longer the distance between point A and point B is, the greater the error when you get to the final pace. For 120 yards, I’d use a compass.

 

Find out if the headings or bearings are in true or magnetic north. I don’t think it’s too great in Illinois but here in WA it makes a huge difference. If it’s not listed on the cache page, email the owner.

 

“Wilderness Navigation” is a great book written by Bob and Mike Burns, available in most bookstores. Short and easy reading. Keep it in the bathroom for the next time you’re sitting.

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Since I'm writing a book on geocaching, I'll take a shot.

 

Bearings offer a way of describing a direction, relative to north, at a given point. Remember that any circle can be divided into 360 equally spaced degrees. If you stood on one spot and wanted to accurately describe your next direction, you could say, "I faced north, then turned clockwise X degrees." In other words, you have told someone to stand in a spot and rotate a certain amount, which will leave them facing the direction in question.

 

A compass provides a good way of measuring a bearing. (Technically it's an azimuth, but most backpackers and hikers use the words interchangably.) Every compass good for this type of navigation has several essential parts:

 

a magnetic needle that rotates and points north (usually it's the red end that points north)

 

a fixed directional arrow that points to the front of the compass

 

a ring (called the azimuth ring) that rotates around the casing holding the magnetic needle

 

an orienting arrow or box that rotates with the ring

 

The orienting arrow points to north on the azimuth ring. (This isn't always true, but we'll get to that in a minute.) If you turn the ring so that north points towards the fixed directional arrow, then turn the compass so that the red end of the needle is directly over the orienting arrow or box, then the directional arrow (and you) are pointed north.

 

To go along a particular bearing, you turn the ring so that the bearing number is at the top of the compass and in line with the directional arrow. Holding the compass horizontally, turn your body so that the red end of the magnetic needle is over the orienting arrow or box. The directional arrow is now pointing in the direction of the specified bearing. Start walking. So long as you keep the magnetic needle above the orienting box, you continue to walk on that bearing.

 

What if you wanted to provide a bearing to someone? That is easy. Hold the compass horizontally and site along it in the direction for which you want a bearing. (You can look at some landmark in the distance to make this easier.) The red part of the needle is, as always, pointing north. Turn the azimuth ring until the orienting arrow or box moves directly under the red part of the needle. The bearing you want will now be at the top of the compass.

 

Now comes the complication. Unfortunately, the magnetic north pole is not in the same spot as the geographic north pole. For most places on earth, there is a magnetic declination, which means at a given location, there is an angle between magnetic north and so-called true north. (For example, in Massachusetts, where I live, the magnetic declination is about 16 degrees west). So when you set a compass to north and "box the needle" (rotate the orienting box or arrow so that it is directly below the red part of the magnetic needle), it actually points to magnetic north, not true north. That is fine, so long as everyone specifies that the bearings are taken with a magnetic north reference.

 

But many people specify bearings to true north, not magnetic north, mostly because maps are generally oriented to true north. In this case, you have to correct for magnetic declination. Checking a local map or appropriate site on the web, you can find your declination. If you have a west declination, then you have to add the number to your bearing to get the "real" bearing from true north. If you have an east declination, then you subtract that amount from the bearing to get the "real" bearing from true north. (Remember: "east is least.")

 

If you don't want to remember to add or subtract, get a compass that has a declination adjustment. Follow the manufacturer's directions to put in the declination. Then all the bearings will reference true north. (Note that the orienting arrow or box will no longer point to the north marking on the azimuth ring. That is fine - just keep boxing the needle and reading the numbers on the dial.)

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Allthough not as easy to use as a compass, my Garmin gives me the option to view my ""track"" on the GoTo screen. Track heading is the actual direction in degrees that you are moving. Start walking and turn slowly until track shows the correct number, 275 degrees in your case. Note you do have to be moving for this to work on most GPSrs!

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If you are given instructions to go x amount of paces or feet at 270 degrees, all you need to do is to rotate the dial until 270 degrees is right at the direction arrow marker. Up to this point you are not worrying about linihg up hte compass with magnetic north.

 

Ok, now turn with the compass until the arrows are "boxed in" with each other. Make sure the red goes with the red, black goes with black...you'll see what I mean.

 

Now, you should be facing 270 degrees if the arrows are boxed in. look for a land feature that's directly in line and go it and then check your bearing again.

 

A pace is equivalent to two steps. However, everyone has their own pace. Thing I like to do is to mark a waypoint where I begin the compass search and when I get to the landmark that's in my line of sight...I'll chekc the gps and do a goto to the waypoint, it will tell me how many feet or at least approx. how many feet I went.

 

Hope this helps.

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quote:
Originally posted by lackdog:

Re: How do you "follow a bearing"?


Well, being rather round and shiny, bearings are rather easy to follow. They generally will just roll downhill, so as long is they don't fall into a hole, you should not have any problems following them.

 

--Marky

"All of us get lost in the darkness, dreamers learn to steer with a backlit GPSr"

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If the cache description does not indicate True or Magnetic in the directions, I wouldn't even try to hunt that cache. With magnetic declination being 14 degrees where I live on the east coast, I've got a 50% chance I'll be off by about 65 yards at the cache location if I have to travel 275 yards.

 

Just a reminder that cache hiders ought to indicate directions as True or Magnetic depending on how you measured it so the finders know which direction to travel too.

 

Tks

 

Alan

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