Hi,

I'm writing a program for Linux that displays position (from GPS) on a
scanned-in chart, and would like it to calculate distance from current
position to the cursor.

How do you calculate distance between two points using lat/long? If
they're due North/South, I can do it ( 1 minute of lat = 1 NM) but how do
you calculate distance from longitude? Perhaps some formula based on the
circumfrence of the Earth at the equator and the latitude?

Lloyd Sumpter

If you have a Bowditch, look under "Sailings" or look in Bowditch online
for the same info.
What you need will be in there.

otn

Lloyd Sumpter wrote:
Hi,

I'm writing a program for Linux that displays position (from GPS) on a
scanned-in chart, and would like it to calculate distance from current
position to the cursor.

How do you calculate distance between two points using lat/long? If
they're due North/South, I can do it ( 1 minute of lat = 1 NM) but how do
you calculate distance from longitude? Perhaps some formula based on the
circumfrence of the Earth at the equator and the latitude?

Lloyd Sumpter

You want http://williams.best.vwh.net/avform.htm

"Lloyd Sumpter" wrote in message
news
Hi,

I'm writing a program for Linux that displays position (from GPS) on a
scanned-in chart, and would like it to calculate distance from current
position to the cursor.

How do you calculate distance between two points using lat/long? If
they're due North/South, I can do it ( 1 minute of lat = 1 NM) but how do
you calculate distance from longitude? Perhaps some formula based on the
circumfrence of the Earth at the equator and the latitude?

Lloyd Sumpter

That will do it - thanks! Curious about how those formulae were developed,
though...

Lloyd


On Thu, 04 Dec 2003 14:46:15 +0000, SpamJam wrote:

You want http://williams.best.vwh.net/avform.htm

"Lloyd Sumpter" wrote in message
news
Hi,

I'm writing a program for Linux that displays position (from GPS) on a
scanned-in chart, and would like it to calculate distance from current
position to the cursor.

How do you calculate distance between two points using lat/long? If
they're due North/South, I can do it ( 1 minute of lat = 1 NM) but how do
you calculate distance from longitude? Perhaps some formula based on the
circumfrence of the Earth at the equator and the latitude?

Lloyd Sumpter

Lloyd Sumpter wrote:

That will do it - thanks! Curious about how those formulae were developed,
though...

Spherical Trigonometry - not for the fain of heart.
--
Dan Best - (707) 431-1662, Healdsburg, CA 95448
B-2/75 1977-1979
Tayana 37 #192, "Tricia Jean"
http://rangerbest.home.comcast.net/TriciaJean.JPG

"Lloyd Sumpter" wrote in message
news

That will do it - thanks! Curious about how those formulae were developed,
though...


I once tried to imagine Bowditch working and refining his tables and
formulas manually. Must have been total dedication.

Steve
s/v Good Intentions
Lloyd


On Thu, 04 Dec 2003 14:46:15 +0000, SpamJam wrote:

You want http://williams.best.vwh.net/avform.htm

"Lloyd Sumpter" wrote in message
news
Hi,

I'm writing a program for Linux that displays position (from GPS) on
a
scanned-in chart, and would like it to calculate distance from current
position to the cursor.

How do you calculate distance between two points using lat/long? If
they're due North/South, I can do it ( 1 minute of lat = 1 NM) but how
do
you calculate distance from longitude? Perhaps some formula based on
the
circumfrence of the Earth at the equator and the latitude?

Lloyd Sumpter

On Thu, 04 Dec 2003 13:20:40 -0800, "Lloyd Sumpter"
wrote:

Hi,

I'm writing a program for Linux that displays position (from GPS) on a
scanned-in chart, and would like it to calculate distance from current
position to the cursor.

How do you calculate distance between two points using lat/long? If
they're due North/South, I can do it ( 1 minute of lat = 1 NM) but how do
you calculate distance from longitude? Perhaps some formula based on the
circumfrence of the Earth at the equator and the latitude?

Lloyd Sumpter

First, an explanatory note:
inverse cos is also known as arc.cos or cos^-1

The great circle distance is given by
Earth radius * arccos [cos Lat1* cos Lat2 * cos (Long1 - Long2)
+ sin Lat1 * sin Lat2]
The Earth (equatorial) radius is
6378 km, or 3963 statute miles or 3442 NM.

Does this help? (There are other formulae for the same result...)

Brian Whatcott Altus OK

It's an academic topic called "Spherical Geometry"
There is a plane which cuts the two coordinate pairs and the Earth
center. A 'triangle' is drawn from the center and the two given
points. The included angle is found from which the great circle
distance is derived.

Brian Whatcott

On Thu, 04 Dec 2003 14:57:11 -0800, "Lloyd Sumpter"
wrote:


That will do it - thanks! Curious about how those formulae were developed,
though...

Lloyd


On Thu, 04 Dec 2003 14:46:15 +0000, SpamJam wrote:

You want http://williams.best.vwh.net/avform.htm

"Lloyd Sumpter" wrote in message
news
Hi,

I'm writing a program for Linux that displays position (from GPS) on a
scanned-in chart, and would like it to calculate distance from current
position to the cursor.

How do you calculate distance between two points using lat/long? If
they're due North/South, I can do it ( 1 minute of lat = 1 NM) but how do
you calculate distance from longitude? Perhaps some formula based on the
circumfrence of the Earth at the equator and the latitude?

Lloyd Sumpter

Fifty seven lurkers just headed for the Tylenols with their heads
spinning, feeling nauseated and dizzy....(c;

I love my Nautical Almanac.....
I love my Nautical Almanac.....
I love my Nautical Almanac.....
I love my Nautical Almanac.....
and GPS...



On Fri, 05 Dec 2003 00:27:38 GMT, Brian Whatcott
wrote:


First, an explanatory note:
inverse cos is also known as arc.cos or cos^-1

The great circle distance is given by
Earth radius * arccos [cos Lat1* cos Lat2 * cos (Long1 - Long2)
+ sin Lat1 * sin Lat2]
The Earth (equatorial) radius is
6378 km, or 3963 statute miles or 3442 NM.

Does this help? (There are other formulae for the same result...)

Brian Whatcott Altus OK


Larry W4CSC

NNNN

"Larry W4CSC" wrote in message
...
Fifty seven lurkers just headed for the Tylenols with their
heads
spinning, feeling nauseated and dizzy....(c;

I love my Nautical Almanac.....
I love my Nautical Almanac.....
I love my Nautical Almanac.....
I love my Nautical Almanac.....
and GPS...

Sounds like the old days with Oscar and his apples (to be
polite).
Oh... The is trig and not the sphere stuff.....

Leanne