GPS

[Guest lostsoul]

What is the equivalent of 1 second in lat/lon coordinates in feet?

[Guest JIntorcio]

Well... The cricumference of the Earth is roughly 25000 miles. Multiply that by 5280 you get 132,000,000 feet. There are 360 degrees all the way around or 360 x 60 x 60 = 1,296,000 seconds. Divide 132,000,000 by 1,296,000 and you get about 102 feet.

[Guest Cape Cod Cache]

No simple answer for that question, a very deep subject. It varies greatly depending on where you are in latitude. http://joe.mehaffery.com has a chart SOMEWHERE in it that will show you just how complex it is ( the world being a sphere and all.) Maps are 'flattened out' bits of a sphere, and have scales on the borders that are for either Lat or Lon. Best of luck...

[Guest Silver]

The 1 second lat readings don't vary too much, as your latitude always starts and stops at the poles and the distance is fairly uniform. But your lon varies by how far north or south you are.

 

For example, 1000 east/west miles at the equator only changes your lon about 1/24 of the circumference of the earth, or about 15 degrees. At roughly 300 miles from either pole, your 1000 mile trip would circle the earth a full 360 degrees.

 

(It reminds me of the old question "What two spots on the earth can you walk 1 mile south, 1 miles east, and 1 mile north and end up at your origninal starting point?" )

 

I found the link at the vast collection at http://joe.mehaffey.com (big list) near the bottom. It pointed to http://home.online.no/~sigurdhu/Grid_1deg.htm where it shows the difference of 1 degree at different lats.

 

Hope this helps. It was something I really hadn't thought too much about before reading your question.

 

Silver

 

[This message has been edited by Silver (edited 02 May 2001).]

[Guest Silver]

The 1 second lat readings don't vary too much, as your latitude always starts and stops at the poles and the distance is fairly uniform. But your lon varies by how far north or south you are.

 

For example, 1000 east/west miles at the equator only changes your lon about 1/24 of the circumference of the earth, or about 15 degrees. At roughly 300 miles from either pole, your 1000 mile trip would circle the earth a full 360 degrees.

 

(It reminds me of the old question "What two spots on the earth can you walk 1 mile south, 1 miles east, and 1 mile north and end up at your origninal starting point?" )

 

I found the link at the vast collection at http://joe.mehaffey.com (big list) near the bottom. It pointed to http://home.online.no/~sigurdhu/Grid_1deg.htm where it shows the difference of 1 degree at different lats.

 

Hope this helps. It was something I really hadn't thought too much about before reading your question.

 

Silver

 

[This message has been edited by Silver (edited 02 May 2001).]

[Guest bob_renner]

quote:

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Originally posted by lostsoul:

What is the equivalent of 1 second in lat/lon coordinates in feet?

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Rough approximations:

1 sec lat ~= 102 ft.

1 sec lon ~= 102 * cos(lat) ft.

 

Bob

[Guest lostsoul]

Thanks guys for the info. At my age (64) I learned something new. The question arose when I compared the readings of two Magellan 315's side by side. There were differences in the reading of the seconds. Will this difference indicates the "accuracy" of the GPS?

 

NOTE: These postings are proof to Puzzled, further on this forum, questioning the benefits of geocaching. It teaches me using my brains again (also figuring out how to get to "cosine") and walking outdoors which my cardiologist prescribed.

 

[This message has been edited by lostsoul (edited 02 May 2001).]

 

[This message has been edited by lostsoul (edited 02 May 2001).]

[Guest Silver]

Lostsoul,

 

I really enjoyed the tutorial on the trimble site. It explains very easily the concepts of location, time, number of sats needed, error types, differential GPS, etc.

 

The web site is http://www.trimble.com/gps/howworks/aa_hw2.htm

 

The site also has a Flash5 version at http://www.trimble.com/gps/howgps/gpsfram1.htm that is a little slower to load but it has some nice animation.

 

Silver

 

[This message has been edited by Silver (edited 02 May 2001).]