Compass: is is possible to calculate my location based on this scenario

[beagle]

Google might be good, but not good enough. Maybe someone here can help resolved this.

I am trying to figure out if it is possible to determine my location when I take a bearing of two mtn tops that are not on the map, if I have pre-drawn a line to the center of the map from each mountain (see attached).

I am able to create my own maps at a scale of 1:20,000 (5cm = 1km) to cover only the area I am going to be in. No reason to carry a 1:50,000 when I am only going to cover 40km in a weekend. 1:20 gives greater detail and most places I go require two maps because the area overlaps from map to map.

I have attached a visual of this problem. Two mountains are located outside of the map that I have in the field. A pre-drawn line from each mountain to the center of the map is marked.

With this info, is it possible to take a bearing and do some calculation to figure out my location

Would I need to put additional info on the map, maybe another bearing to each mountain from another location on the map?

[Rick]

The least number of points you can use to determine your location is three. Triangulation is required. Otherwise, you have the right idea. Just draw a line on the map from the 1st reference point back toward you. Do the same thing with the second reference point and the third. Where the three lines intersect is where you are.

I have to temper that with saying it works well with commercial maps. I have no idea how it will work with hand drawn maps because the accuracy of the map will determine how accurate your triangulation is. A topo is obviously the best because you can then compare the cross point on the map to the surrounding terrain and know with certainty where you are.

[Sarge47]

Like Rick said! I would suggest you start out with the "Topo," then transfer the pertinent info to your hand drawn map.

[Delta 5168]

Beagle, here in FayetteNam, NC, we have a hobby shop that specializes in cutting and laminating topo maps. You might want to check around in your area for a map shop or copy store that could do that for you, then fold to the area you want. Also, might be a good idea to leave a copy of that DIY map with a trusted friend before you head to the boonies - just in case!

[Rick]

I had to leave earlier but gave this some thought and decided a bit more explanation might be in order.

You can find your point using 2 back bearings but if you've made and error you'll never know it. Let's assume you take two back bearings, find your place on the map and start walking. What you didn't realize is the point in the distance is NOT the point on the map you used. You made a mistake but it looks right and you start walking into never never land.

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If you take a third reading you will see that error. If your lines don't intersect but form a triangle like the one below then you know that one or both of your first two back bearings were wrong.

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If, on the other hand, your third back bearing intersect the first two then you know your back bearings are correct and your location is assured. Since it only takes a couple of minutes to shoot a back bearing it seems prudent to me to take the time to ensure you are correct especially if you are hiking a longer distance when a small error could amount to several miles.

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Hopefully, that's a better explanation.

[Old GI]

Beagle, here in FayetteNam, NC, we have a hobby shop that specializes in cutting and laminating topo maps. You might want to check around in your area for a map shop or copy store that could do that for you, then fold to the area you want. Also, might be a good idea to leave a copy of that DIY map with a trusted friend before you head to the boonies - just in case!

Hey Delta, you better watch out - there might still be some of them FayetteCongs around (Haven't been there since 92; 3 tours over the years prior). Speaking of land nav, while in Phase 1 (SFOC), I jokingly said "my idea of land nav was an ESSO road map and a jeep with driver; not well received but I had ample opportunity to learn from the best. I also told them I had developed a system that I could tell where I was under any conditions - put your left arm straight to your front and your right arm straight out to the side ----- and where they meet is exactly where you are. Decorum prevents my description of how the instructors reacted to that one.

[intothenew]

..........With this info, is it possible to take a bearing and do some calculation to figure out my location..........

Yes, but it involves a rather elaborate set of calculations. It can be done with a pencil, compass, and trig sheet/calculator. Or, it can be done with a pencil, protractor, and scale. Since you are asking the question, I assume that your geometry/trigonometry is not capable. I mean no disrespect in that statement. If you have a coordinate scale and protractor, I can walk you through it. It will require building a scale model, on the back of the map, or preferably on grid paper.

[intothenew]

If you will leave with a scale model of the two mountains and that known point on grid paper, it makes things rather simple.

In this example, I know where I am relative to the known point, each mountain, and after a radio conversation my long haired friend.

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[kyratshooter]

I have never been called to navigate off a single point unless I was in training and the point was just over the next ridge. Navigation normally depends on a series of points used as reference as one travels. When given objectives one scours the map for reference points immidiately; type of tarrain such as saddles or ridges , streams, cliffs, thick woods or open fields. I was always looking for quick pace count reference points, rally points and danger zones. You use those as indicators that you are on track, not trig and geometry to survey in to the final objective with no reguard to what is between here and there.

Over the river and through the woods, just passed the third tree and Grandmas house should come into view soon. You don't just go out wandering around looking for Grandma's house.

Just like on a road map. If I am going from TN to Kalifornia I need to go through Arkansas, OK and Texas. If I see a sign that says Kansas I have gone a bit too far north! This is much easier to do if you know where you took the wrong turn, saw that you were no longer on I-40 or noticed that you were going north rather than west a few hours earlier.

If you try to use graph paper and hike 12 clicks at 270 degrees to point A, through rough tarrain, you are going to miss your mark by a good bit. Even if you are on flat tarrain you are going to lean right or left a bit with each step. This is one reason a person picks a bearing point(reference point) and walks to that point, then the next point.

Absolute best solution? Take out your smart phone and turn on the GPS.

[Rick]

Yes, but it involves a rather elaborate set of calculations.

And how would you know if you made a mistake? All of that on the wrong reference point on the map even if the calculations are right? Kyrat did that once going to Texas and wound up in St. Louis. When he saw the arch he knew he'd done wrong. Either that or was at the world's largest Mcdonalds.

[hunter63]

Well, as the directions were given to California, in the movie "The Frisco Kid"...."Follow the setting sun, straight as pi$$ till you hit the big water, then turn left."

I guess I never have used a compass to do navigation like this, but agree it would be a good skill to learn.......Most of mine has always been, "I came in here "X"....and I want to go there "X"......what kind of crap is in my way", the shortest distance isn't always the best route.

Sorry Krat, smart phones only work till the battery does dead.....Yeah I know was kinda tongue in cheek, right?

[Rick]

I refuse to use a phone that's smarter than me. My cell phone is still a dial phone.

[beagle]

thanks for all the replies.

Just to clarify
- I make my own maps, from government digital information, these are not hand drawn. They arejust like the topo maps you can buy, but I can customize them with more or less info as required and I don't have to worry about matching to maps side by side.

- the sighted points are not on the map. Due to the size of the map, and the scale - these mountains are not included, but they are visible when you are hiking.
In my region - British Columbia, I have lots of points to reference.


I have resolved it with this idea -- see below.

This allows you take a back bearing on the mountain and then draw the line appropriately. I agree it takes three points to get an accurate triangle. This just requires adding an additional compass around another mountain.
compass question v01.jpg

Again - thanks for all the feedback and info.

[intothenew]

I actually have two known reference points to cross check, that's one. I can move, a given distance and direction, and cross check both of those reference points. Even without the model or map, I can calculate the distance to any object by the second method.

As to choosing the wrong reference point/points, certainly I would cross check back to my surroundings versus the map that I have. Path to follow would also be weighed from the information on the map. Just because it is a grid does not mean that you have to travel in straight lines. You can simply check and cross check by these methods.

[Rick]

ITN - It seems a tad complicated but if it works for you then....you know the rest. Just shows there's more than one way to skin a cat.

[Delta 5168]

I can imagine! Probably went over as well as me telling a SGM that the chow line gravy he was admiring looked like what I cleaned out of the mess hall grease trap that morning on zero week KP! Oh well, Camp Lejeune has chemicals in their water; Ft. Bragg must have "stupid"! I was just a leg, but a lot of Army rubbed off on me in a short time. Which group? Sorry I got off subject. Tell the guys about the STAR nav course. I want to set up one of those for my grandsons.

[JPGreco]

Intothenew, that system will work, but as stated, you should add in another reference point if you can. Being off by a few degrees can greatly affect your location or future location. However, to answer your original question, yes, you can figure out basically where you are with two reference pts on any map. The reality is it is simply where your two reference lines cross. The addition of a 3rd reference is to make sure the others are correct as Rick pointed out. I don't believe you need any trig because you can't know the exact distance when taking your reference lines, and you already know the angle. Your map will give you an idea of how far away you are from either given point and I can't see the need of finding how far apart those two points are when hiking. Again, your map would be able to tell you that info as well.