Replicated from the GGA EZBoard:

nasty george
Registered Geocacher
(4/24/02 2:41:05 pm)
one minute of arc

I have thought long and hard about how to share this, and since you are obviously from a myrid of backgrounds, I have decided to make it very simple and I hope you can make use of it. It is based upon a perfectly spherical earth which is not the case and it attempts to make a plane surface out of a spherical surface. The following method is approximate but so are the gpsr's. It is based upon the earth's radius as 20,906,000 feet which is approximate (it varies).
In latitude, you can convert minutes of arc to feet or feet back to arc by:
1'=6080 feet
.1'=608 feet
.01'=60.8 feet
.001'=6.1' feet
In longitude arc varies according to how far you are from the equator. so for the state of Georgia.
at 32 degrees latitude...5,155 feet
33 ....5,100 feet
34 ....5,040 feet
35 ....4,980 feet
You can fill in the .1, .01,.001 values.
You can use these values on caches where you start out at a given position and walk due North so many feet and then due east so many more feet. You simply convert the feet to minutes and add or subtract them to the starting position to get the position of the end point. For those having a working knowledge of trigonometry and geometry, there are many little things you can do with the above to make your caching more enjoyable. Please understand that all of this is approximate so don't try to push it beyond a few thousand feet and it should remain within the accuracy of your gpsr.
I will be glad to share with you the derivation and limitations of all this via email if you wish. In closing, take the number of feet in 1 minute of arc at the equator +-6080 and convert it to nautical miles. That may be of some interest and is a clue to where the knot came from.


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erik88l r
Administrator
(4/24/02 2:45:42 pm)
Re: one minute of arc

That's very interesting! I'm in the process of designing my next cache hunt in which knowing this will be helpful to the hunter


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the mtn man
and puppymonster
(4/24/02 5:44:30 pm)
Re: one minute of arc

Now that scares the dickens out of me to see erik write that!


Very interesting information, NG.


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Da Rebel
Super Poster
(4/24/02 8:10:21 pm)
Re: one minute of arc

What's really scary to me is that the Earth's radius varies!


"If you tell the truth, you don't have to remember anything." - Mark Twain


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erik88l r
Administrator
(4/24/02 8:53:59 pm)
Re: one minute of arc

I think the earth (like many of us) bulges out around the equator. I attribute my bulge to the centrifugal effects of spinning around a lot


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llhGA
Registered Geocacher
(4/25/02 10:06:09 pm)
Re: one minute of arc

Would it surprise anyone to know that the atmosphere is significantly thicker around the equator than at the poles? The flow of atmosphere (wind), like water pouring toward the poles, combined with the rotation of the earth and the cold polar air meeting it, is what causes the powerful river of air called the jetstream.