compass and gps together

[+n8aho]

I am just starting to learn how to use my compass along with my gps on geo hunts. I have my gps set up to display bearing to the cache in degrees true. I live in area where we have about 7 degrees west declination. Say I am getting a bearing off of my gps of 180 degrees to the cache.... to correctly transfer this info over to my compass so I can use it I add the 7 degrees to the 180 degrees for a magnetic bearing of 187 degrees.....is this the correct way do do this?

 

Thanks,

Jim

 

Sommes-nous perdus encore?

[Tahosa and Sons]

In order to make these two instruments talk to each other set your GPS to mag. If you use a map the learn how to use UTM's. Make sure you match you map datum to your GPS datum. Also a compass that is adjustable for declination will alleviate any problems with any conversions.

These links should be helpful to you.

http://www.maptools.com/UsingUTM/index.html

http://www.isu.edu/outdoor/OutMap.htm

http://www.netside.com/~lcoble/dir9/land_nav.htm

http://maps.nationalgeographic.com/topo/

http://www.education.qld.gov.au/tal/kla/compass/index.html

http://www.princeton.edu/~oa/manual/mapcompass.shtml

http://celia.mehaffey.com/dale/measure.htm#grids

http://celia.mehaffey.com/dale/wgarmin.htm#toc

Good Luck and Happy Caching

 

The "Bushwhacker"

Exitus acta probat

>>--->

[+n8aho]

Thanks Bushwacker that sure was a fast reply...will follw the links.

 

Jim

 

Sommes-nous perdus encore?

[+Trees]

Are you sure there is that much difference between True North and Magnetic North? We here in the midwest are closier to Magnetic north than those out west. My Topo map for my area here at Indianapolis shows only about a 1/2 degree difference in 1980. But yes, you would have to correct for the difference if your gps is set for True north. If you had it set up for Magnetic north, no correction needed. Hope this helps. I too just started this year and have been having tons of fun doing the caching thing.

 

"Trees"

[+brdad]

quote:

---

Originally posted by trees:

Are you sure there is that much difference between True North and Magnetic North?

"Trees"

---

 

Make sure you use current numbers when figuring magnetic variation. It changes daily! Not noticable, mind you, but a 1980 map could have a significant difference. I depends on where you are as to how big a difference it makes. My GPS displays what the local declination is, I would think the all do?

Here in Maine, it is currently about 18º West. I have a 1981 map here shows 19ºW, and a 1902 map with 17.2ºW variation.

 

I do find it hard to imagine it is 1/2º in Indiana and yet 7º in Ohio.

 

I do agree it's easier to let the GPS convert to magnetic rather than doing it yourself for geocahing.

 

Keep Earth clean, it's not Uranus.

[+Don&Betty]

You can measure the present declination in your area yourself. Just find a road that is shown on a topo map to run precisely "true" north-south (or east-west), perhaps the street in front of your house. Then just go out there, sight your compass straight down the road, and simply read how far off the needle points from the "true" north (or east) direction of the road.

[Tahosa and Sons]

Here is another link for that Magnetic Problem.

"My notes wont stay on the Refrigerator"

http://www.geocities.com/magnetic_declination/

 

The "Bushwhacker"

Exitus acta probat

>>--->

[+unclerojelio]

I never get this right unless I'm looking at my compass (which I don't have at the moment) but I think in this case you need to subtract the declination to get the proper azimuth.

 

... Two roads diverged in a wood, and I--

I took the one less traveled by, ...

 

unclerojelio

[TrollGRG]

I agree that it is easier to let the GPS do the work but if you want to get comfortable with the compass (which everyone should) you may want to do this as mental exercises for yourself.

 

Having said that, generally speaking, if your variation/declination is EAST then the magnetic bearing will be LEAST (smaller). Conversly, if the variation/declination is WEST then the magnetic bearing is BEST (bigger).

 

If you have both the true bearing and the variation but you don't know if you are supposed to add it or subtract it then follow that simple rule.

 

e.g. True Bearing of 097 degrees with a variation/declination of 3 degrees east will give you a magnetic bearing of 097 - 003 or 094 degrees.

 

A Troll, A Lady and Duncan the Dog

[+CYBret]

The most important discovery for me about using a GPS and compass together is overcoming the problems of using a GPS in dense tree cover.

 

It never fails that when I'm out in the woods, doin' the "drunken bee dance" I'll notice that the pointer/compass on my Venture's Navigation page isn't keeping up with the twists and turns I'm making. When that happens I pull out the compass (a new Silva, I gave up on the cheaper ones) and find North. Then I turn the Venture to match it's compass with the Silva, and follow the arrow right to the cache.

 

The first time I discovered this, I turned the Venture to north, looked where the arrow was pointing and spotted the cache immediately.

 

Bret

 

"The kingdom of heaven is like treasure hidden in a field.

When a man found it, he hid it again."

Mt. 13:44

[+Desert_Warrior]

quote:

---

Originally posted by trees:

Are you sure there is that much difference between True North and Magnetic North? We here in the midwest are closier to Magnetic north than those out west. My Topo map for my area here at Indianapolis shows only about a 1/2 degree difference in 1980.

---

 

El Paso, Texas, which is further south and west of you, has 11 degrees of declination as of 1994,

which is the last year I taught land-nav in the army. Dunno what it is today, but I bet it hasn't changed more than one degree, and I doubt you can read, or walk, with one degree of accuracy cross-country. Especially after afew beers, or whatever. So that would be close enough.

 

HTH.

 

Mike. KD9KC.

El Paso, Texas.

 

Seventeen minutes after her FIRST call for help, police officers arrived to find Ronyale White dead.

 

Prohibiting self defense is the ultimate crime. Police carry guns to protect themselves. What protects YOU ???

[+Lost & Found]

Seventeen minutes after her FIRST call for help, police officers arrived to find Ronyale White dead.

 

Prohibiting self defense is the ultimate crime. Police carry guns to protect themselves. What protects YOU ???

 

A Colt.45 semi-auto

 

What I do today is Important - I spent a day in my life doing it.

[+Lost & Found]

Seventeen minutes after her FIRST call for help, police officers arrived to find Ronyale White dead.

 

Prohibiting self defense is the ultimate crime. Police carry guns to protect themselves. What protects YOU ???

 

A Colt.45 semi-auto

 

What I do today is Important - I spent a day in my life doing it.

[+Alan2]

Compute Values of Earth's Magnetic Field to find your declination where ever you are and you can see what it was by different dates.

 

United States Magnetic Field Charts for 1995 shows the mainland US's declination idicating 0 in the middle more or less and increasing as you go west or east. Check te middle "declination" map.

 

ALan

[+mikedx]

I forgot that I could convert the GPS to magnetic north. But I really wasn't concerned over the minor differences.

 

I found a remedy to the arm waving for the nonmagetic compass GPS's. I just get the bearing off the GPS and line up my compass and follow it. It saves from walking back and forth when you are on the side of a mountain.

[+Brown Dwarf]

OK, so I'm a techie nerd. I always use both a compass and a GPS. The caches out here in the Pacific North Wet are often under medium to heavy tree cover -- and in areas with extensive networks of informal trails. Even a good GPS can be jumpy. When I hunt with a partner, she drives the GPS, and gives me range and bearing. I drive the compass and convert her input into which way to turn. We've found it to be fast and accurate. It also keeps the GPS far enough away from the compass so the electronics don't affect it.

 

As for magnetic vs. true, either system will work -- but both the compass and GPS should be speaking the same language.

 

My GPS [Garmin 12 XL] offers both options, although the factory default is magnetic. The better compasses give you a way to correct for declination, which runs almost twenty degrees around here. In short, you can run either on magnetic bearings or true. I run both the compass and GPS on true, rather than magnetic, so they agree with the maps. Pilots and sailors, who work in a larger area, generally go with magnetic headings, correcting to true as needed.

 

[i missed a cache a while back because the GPS was giving me a magnetic heading -- which I took to be true. I've since reset the GPS to give me true headings. Resetting the compass to take out the correction for declination would also have done the trick.]

 

To really remember how to correct, find a road with a section at least a mile long and running either east/west or north/south. Drive it and note what the GPS is indicating. Mine said I was going on a heading of 71 degrees [magnetic], when the map told me I was going due east -- or 90 degrees [true]. So around here, subtract about twenty degrees to go from true to magnetic -- and add about twenty degrees to go from magnetic to true.

 

Hope this helps,

B

[+Trees]

I just checked my location(Indpls,Ind) on the site listed by Alan2 and it shows the correction for me to be 3degrees west. So its not such a difference in 20 years. Also using the second listing, the map shows a large difference between my location and eastern Ohio. Thanks for the info, I didnt know where to look for the latest correction. When I was working on aircraft 20 years ago,I was talking with some pilots and they said that here in the midwest the difference wasnt worring about. The map shows that to be true if you are in Ill or western Ind. Boy, you sure get to learn a lot doing this "hobby".

[+EScout]

As a Scoutmaster who teaches compass in an area with a large declination (14 E), it is very important to get it right. For Geocach purposes, I would recomend :

GPS set to true.

Use a compass with the declination adjustment. Some, like the Brunton Classic 9020G, have the inner part adjustable for declination. Set it once, and when the needle is lined up with the marker, you are reading true on the outer azimuth ring. Very easy-no adding or subtracting.

[+RichMaru]

To tell the truth, I haven't been paying much attention to the difference between true and magnetic north. Most of the time the difference is not that great, and if your GPS has good reception all the way to the cache, you will find it anyway.

 

To put it another way, if you read the bearing off your GPS, and then use that reading to point yourself with a compass, you will be off by the amount of the declination. Now let's say you just follow that "crooked arrow". You may not go straight toward the cache, but you will get closer. And as you get closer, still using the GPS to get bearings, the crooked arrow will turn because you are about to pass the cache. So you turn and keep walking. This is called "homing," but since your readings are slightly off, you don't go straight toward the cache, but instead you spiral into it. But you still eventually get there (GPS accuracy notwithstanding).

 

My two cents,

Rich

[+Ellteejak]

After lots of trouble that still exists for me. Do the following:

 

1. Use a compas set for Actual North (via a declination setting adjustment against the magnetic north). Know what this is, and be prepared to cahnge to magnetic north if you can not find the cache.

 

2. Always ALWAYS ALWAYS!!! Check your GPS against a benchmark know location for a survey marker. You may find your GPS is off by 100 feet (I did).

 

3. Use mapping software (like WWW.TOPOZONE.COM on the internet or buy National Geographic TOPO! stateseries for your state) to map out the location of the CACHE. Then you can use the map (maybe) and landmarks and the compass to find things (maybe).

 

Good luck.

[+headmj]

I have been very successfully using my meridian with a simple Silva compass that Escout would recognize (scoutmaster Allegany-Highlands 9 years). The Meridians (and others I believe)have a declination table built into them so they can correct at your lat/long. It is then a simple case of setting the heading on the compass and walking in the direction shown by the needle. In case no one has ever given you this hint, when you sight along the direction arrow, look for a distant landmark to walk towards (tree, boulder, etc) this will be much easier and accurate than walking with the compass in your hand. Also, instead of doing the dance of the drunken bee as you home in on your cache, when you get within 100 ft take a compass bearing and look down that line for landmarks, then move perpendicularly about 100 ft and do it again. Try to see where the 2 imaginary lines cross and you will have a very good approximation of the cache location. Go there and let your GPS settle down and try again.

[+OzzieSan]

quote:

---

Originally posted by ktjensen:

After lots of trouble that still exists for me. Do the following:

 

1. Use a compas set for Actual North (via a declination setting adjustment against the magnetic north). Know what this is, and be prepared to cahnge to magnetic north if you can not find the cache.

 

2. Always ALWAYS ALWAYS!!! Check your GPS against a benchmark know location for a survey marker. You may find your GPS is off by 100 feet (I did)...

---

 

What type of "benchmark" were you using? I hope it was a higher order horizontal! If you used a vertical you were lucky to only be off 100 feet.

 

If you are finding that you are always off 100 feet or more you may want to send your GPSr back for a checkup.

[+apersson850]

And if you use a GPS with a built-in compass, like my Vista, it doesn't matter at all, since the GPS will show you the bearing to your target, even if you enter a User deviation of 180º, effectively turning the world upside down. As long as you follow that GPS, and that only, it will work anyway.

 

The same goes for any GPS, except that it will stop knowing the direction as soon as you stop moving in any direction.

 

Anders