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Date: 04 Jul 2007 04:06:55
From: W. Watson
Subject: Determining the Distance Between Two Points on the Earth's Surface
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I have this link <http://www.wcrl.ars.usda.gov/cec/java/lat-long.htm > for
the topic in the Subject line, but it is broken. Does anyone have one that
uses both lat/long of the names of cities to compute the distance?
--
Wayne Watson (Nevada City, CA)
Web Page: <speckledwithStars.net >
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Date: 05 Jul 2007 14:54:50
From: thad@thadlabs.com
Subject: Re: Determining the Distance Between Two Points on the Earth's Surface
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On Jul 4, 3:45 pm, laura halliday <marsga...@hotmail.com > wrote:
> On Jul 4, 2:23 pm, "t...@thadlabs.com" <t...@thadlabs.com> wrote:
>
> > One of the tech notes for a "gcdist" program I wrote and posted to
> > sci.math about 20 or so years ago provides insight to the calc; only
> > online ref I found is here:
>
> > <http://groups.google.co.jp/group/sci.math/msg/d6c891302914fd84?
> > dmode=source&hl=ja>
>
> Maybe I'm behind the times, but for two places that
> close together I'd look in an atlas, use the distance
> scale, and have an answer in under 10 seconds.
>
> Even if they weren't on the same map, I could still
> read off the coordinates and punch them in to a
> calculator.
>
> Am I missing something?
Accuracy. and speed. For all intents and purposes, my gcdist
calculates the distance in less than the time required for the
cursor to zip to the left margin to begin displaying the answer.
:-)
A lot depends on one's needs. I often need both bearing and
distance between 2 points (even) in the same town; one example
of how I used the answers appears in the first 7 lines displayed
here (of ClearSkyClocks flanking me within 10 miles):
<http://thadlabs.com/ASTRO/view-bracket.htm >
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Date: 04 Jul 2007 15:45:54
From: laura halliday
Subject: Re: Determining the Distance Between Two Points on the Earth's Surface
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On Jul 4, 2:23 pm, "t...@thadlabs.com" <t...@thadlabs.com > wrote:
> One of the tech notes for a "gcdist" program I wrote and posted to
> sci.math about 20 or so years ago provides insight to the calc; only
> online ref I found is here:
>
> <http://groups.google.co.jp/group/sci.math/msg/d6c891302914fd84?
> dmode=source&hl=ja>
Maybe I'm behind the times, but for two places that
close together I'd look in an atlas, use the distance
scale, and have an answer in under 10 seconds.
Even if they weren't on the same map, I could still
read off the coordinates and punch them in to a
calculator.
Am I missing something?
Laura Halliday VE7LDH "Que les nuages soient notre
Grid: CN89mg pied a terre..."
ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte
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Date: 07 Jul 2007 07:53:47
From: W. Watson
Subject: Re: Determining the Distance Between Two Points on the Earth's Surface
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Not at all, but I can find my bookmarks for such matters much faster--until
they expire. :-)
laura halliday wrote:
> On Jul 4, 2:23 pm, "t...@thadlabs.com" <t...@thadlabs.com> wrote:
>
>> One of the tech notes for a "gcdist" program I wrote and posted to
>> sci.math about 20 or so years ago provides insight to the calc; only
>> online ref I found is here:
>>
>> <http://groups.google.co.jp/group/sci.math/msg/d6c891302914fd84?
>> dmode=source&hl=ja>
>
> Maybe I'm behind the times, but for two places that
> close together I'd look in an atlas, use the distance
> scale, and have an answer in under 10 seconds.
>
> Even if they weren't on the same map, I could still
> read off the coordinates and punch them in to a
> calculator.
>
> Am I missing something?
>
> Laura Halliday VE7LDH "Que les nuages soient notre
> Grid: CN89mg pied a terre..."
> ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte
>
--
Wayne Watson (Nevada City, CA)
Web Page: <speckledwithStars.net >
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Date: 11 Jul 2007 19:40:20
From: Stuart Levy
Subject: Re: Determining the Distance Between Two Points on the Earth's Surface
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laura halliday wrote:
>> On Jul 4, 2:23 pm, "t...@thadlabs.com" <t...@thadlabs.com> wrote:
>>
>>> One of the tech notes for a "gcdist" program I wrote and posted to
>>> sci.math about 20 or so years ago provides insight to the calc; only
>>> online ref I found is here:
>>>
>>> http://groups.google.co.jp/group/sci.math/msg/d6c891302914fd84?dmode=source&hl=ja
>>
>> Maybe I'm behind the times, but for two places that
>> close together I'd look in an atlas, use the distance
>> scale, and have an answer in under 10 seconds.
>>
>> Even if they weren't on the same map, I could still
>> read off the coordinates and punch them in to a
>> calculator.
>>
>> Am I missing something?
>>
>> Laura Halliday VE7LDH "Que les nuages soient notre
>> Grid: CN89mg pied a terre..."
>> ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte
Oh cool. The haversine version is a really handy formula --
adapting from Thad P Floryan's posting above,
hav Distance = hav (Lon1 - Lon2) * cos Lat1 * cos Lat2 + hav (Lat1 - Lat2)
(it even looks like the Pythagorean formula, c^2 = a^2 + b^2,
with the longitude leg weighted by the cosines of both latitudes!)
where hav A = sin^2 (A/2), so
Distance = 2 * asin( sqrt( sin((Lon1-Lon2)/2)^2 * cos(Lat1) * cos(Lat2) + hav((Lat1-Lat2)/2)^2 ) )
This looks much better for computation than the "acos" version mentioned
in the orig. posting, since for small angles (short distances),
the arccos is very insensitive to its input, so errors will be huge.
Not so for the haversine. Its accuracy should be OK except when
the arcsine (asin) is near 90 degrees, so Distance is near 180 deg,
i.e. it only fails for nearly antipodal points.
Stuart Levy in sunny Champaign, IL
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Date: 07 Jul 2007 11:41:36
From: SkySea
Subject: Re: Determining the Distance Between Two Points on the Earth's Surface
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If you have a spreadsheet, create a formula to find the distance. For
the cell formula below, it refers to four columns to the left:
longitude1 (in Column A...), latitude1, longitude2, latitude2 (...in
Column D):
=(60*DEGREES(ACOS(SIN(RADIANS(B30))*SIN(RADIANS(D30))+COS(RADIANS(B30))*COS(RADIANS(D30))*COS(RADIANS(A30-C30)))))
The result is given in nautical miles. 1M = 1.852km = 1.150782mi
It's wordy because Excel (Quattro for DOS too, and probably for
Windoze) uses radians.
=============
- Dale Gombert (SkySea at aol.com)
122.38W, 47.58N, W. Seattle, WA
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Date: 04 Jul 2007 14:23:47
From: thad@thadlabs.com
Subject: Re: Determining the Distance Between Two Points on the Earth's Surface
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On Jul 4, 8:28 am, laura halliday <marsga...@hotmail.com > wrote:
> [...]
> Assuming a spherical Earth,
>
> cos(distance) = sin(lat1)sin(lat2) + cos(lat1)cos(lat2)cos(lon1 -
> lon2)
>
> ...as published in every reference book on the subject for
> the last couple of centuries.
>
> For small distances the Earth is approximately flat and you
> can use Pythagoras.
One of the tech notes for a "gcdist" program I wrote and posted to
sci.math about 20 or so years ago provides insight to the calc; only
online ref I found is here:
<http://groups.google.co.jp/group/sci.math/msg/d6c891302914fd84?
dmode=source&hl=ja >
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Date: 04 Jul 2007 10:15:00
From: canopus56
Subject: Re: Determining the Distance Between Two Points on the Earth's Surface
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On Jul 4, 9:52 am, "W. Watson" <wolf_tra...@invalid.com > wrote:
> Thanks for the computational tips, but I'm looking for a site that one
> simply enters the lat/long or gives the names of two cities of two points
> and produces the results. It's often the ability to use city names that
> makes the broken link site very attractive.
Lat long input
http://www.fcc.gov/mb/audio/bickel/distance.html
http://woodshole.er.usgs.gov/staffpages/cpolloni/manitou/ccal.htm
City to city input
http://www.airport-accommodation.co.uk/worlddistances.php
http://www.airport-accommodation.co.uk/distance-calculator.php
(Europe)
http://www.airport-accommodation.co.uk/usa-distance-calculator.php
(USA)
About:
http://en.wikipedia.org/wiki/Great_circle_distance
- Canopus56
P.S. For West Coast and Intermountain lurkers, the great circle
bearing is useful for computing the direction between your o.p. and
Vandenberg A.F. in order to look for booster launches.
Vandenberg launch schedule
http://www.spacearchive.info/vafbsked.htm
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Date: 04 Jul 2007 08:28:42
From: laura halliday
Subject: Re: Determining the Distance Between Two Points on the Earth's Surface
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On Jul 4, 4:06 am, "W. Watson" <wolf_tra...@invalid.com > wrote:
> I have this link <http://www.wcrl.ars.usda.gov/cec/java/lat-long.htm> for
> the topic in the Subject line, but it is broken. Does anyone have one that
> uses both lat/long of the names of cities to compute the distance?
Assuming a spherical Earth,
cos(distance) = sin(lat1)sin(lat2) + cos(lat1)cos(lat2)cos(lon1 -
lon2)
...as published in every reference book on the subject for
the last couple of centuries.
For small distances the Earth is approximately flat and you
can use Pythagoras.
For large distances and high accuracy (or just plain
geekness :-) Meeus describes a procedure in Astronomical
Algorithms that originated with the Bureau des Longitudes,
which takes Earth's flattening in to account. You'll need
to look that one up yourself...
Laura Halliday VE7LDH "Que les nuages soient notre
Grid: CN89mg pied a terre..."
ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte
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Date: 04 Jul 2007 08:52:40
From: W. Watson
Subject: Re: Determining the Distance Between Two Points on the Earth's Surface
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Thanks for the computational tips, but I'm looking for a site that one
simply enters the lat/long or gives the names of two cities of two points
and produces the results. It's often the ability to use city names that
makes the broken link site very attractive.
Ah, I had the following bookmarked <http://www.indo.com/distance/ >. I was
trying to find the distance between Challis, ID and Nevada City, CA last
night and finally used the true lat/long of each of these cities with some
site. However, I had to first find the lat/long of each with Google. This
one took the names of each and got it right. Challis has a pop. of about 900
and Nevada City, where I live, has a pop. of about 3,000. According to my bk
mrk, the site is called "How far is it? Crow Fly Distances". I was quite
impressed it even knew where Challis, ID was. It looks like I added "Crow
Fly ...".
Another advantage to the above is the variety of formats it handles. Many
sites do not allow 45.5 for 45 degrees and 30 minutes.
laura halliday wrote:
> On Jul 4, 4:06 am, "W. Watson" <wolf_tra...@invalid.com> wrote:
>> I have this link <http://www.wcrl.ars.usda.gov/cec/java/lat-long.htm> for
>> the topic in the Subject line, but it is broken. Does anyone have one that
>> uses both lat/long of the names of cities to compute the distance?
>
> Assuming a spherical Earth,
>
> cos(distance) = sin(lat1)sin(lat2) + cos(lat1)cos(lat2)cos(lon1 -
> lon2)
>
> ...as published in every reference book on the subject for
> the last couple of centuries.
>
> For small distances the Earth is approximately flat and you
> can use Pythagoras.
>
> For large distances and high accuracy (or just plain
> geekness :-) Meeus describes a procedure in Astronomical
> Algorithms that originated with the Bureau des Longitudes,
> which takes Earth's flattening in to account. You'll need
> to look that one up yourself...
>
> Laura Halliday VE7LDH "Que les nuages soient notre
> Grid: CN89mg pied a terre..."
> ICBM: 49 16.05 N 122 56.92 W - Hospital/Shafte
>
--
Wayne Watson (Nevada City, CA)
Web Page: <speckledwithStars.net >
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Date: 04 Jul 2007 14:34:36
From: Shawn
Subject: Re: Determining the Distance Between Two Points on the Earth's Surface
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W. Watson wrote:
> Thanks for the computational tips, but I'm looking for a site that one
> simply enters the lat/long or gives the names of two cities of two
> points and produces the results. It's often the ability to use city
> names that makes the broken link site very attractive.
>
> Ah, I had the following bookmarked <http://www.indo.com/distance/>. I
> was trying to find the distance between Challis, ID and Nevada City, CA
> last night and finally used the true lat/long of each of these cities
> with some site. However, I had to first find the lat/long of each with
> Google. This one took the names of each and got it right. Challis has a
> pop. of about 900 and Nevada City, where I live, has a pop. of about
> 3,000. According to my bk mrk, the site is called "How far is it? Crow
> Fly Distances". I was quite impressed it even knew where Challis, ID
> was. It looks like I added "Crow Fly ...".
>
> Another advantage to the above is the variety of formats it handles.
> Many sites do not allow 45.5 for 45 degrees and 30 minutes.
Google Earth has a handy distance function. If you mean Nevada City,
CA, it shows 503 miles. I don't know haw accurate it is though.
Shawn
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Date: 04 Jul 2007 13:38:37
From: Chris L Peterson
Subject: Re: Determining the Distance Between Two Points on the Earth's Surface
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On Wed, 04 Jul 2007 04:06:55 -0700, "W. Watson"
<wolf_tracks@invalid.com > wrote:
>I have this link <http://www.wcrl.ars.usda.gov/cec/java/lat-long.htm> for
>the topic in the Subject line, but it is broken. Does anyone have one that
>uses both lat/long of the names of cities to compute the distance?
Try http://williams.best.vwh.net/ . There is a good practical treatment
of spherical geometry problems, as well as Javascript calculators and a
comprehensive Excel spreadsheet.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 04 Jul 2007 11:22:54
From: didereaux
Subject: Re: Determining the Distance Between Two Points on the Earth's Surface
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"W. Watson" <wolf_tracks@invalid.com > wrote in
news:P9Lii.442$bz7.357@newssvr22.news.prodigy.net:
> I have this link <http://www.wcrl.ars.usda.gov/cec/java/lat-long.htm>
> for the topic in the Subject line, but it is broken. Does anyone have
> one that uses both lat/long of the names of cities to compute the
> distance?
Simple trig really. COSINE of theta=difference in northings/difference
in eastings. However for large distances on the earth it becomes"
COSINE of theta=difference in northings/difference in eastings*(latitude
factor)
The factor corrects for convergence of the lines of longitude as you near
the poles. Okay, okay I understand, you want it now, from somebody
else...go to Naval Observatory site and dig around I believe they had a
java thingy that does it for you, if not then they do have the -factor-
values and I presume since you are in a science newsgroup you can use a
basic calculator that has trig functions. Oh yeah, many navigation sites
also have all of this info as well as java calculators. ;)
g'Luk
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Date: 04 Jul 2007 11:28:40
From: Eugene Griessel
Subject: Re: Determining the Distance Between Two Points on the Earth's Surface
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didereaux <cajun@mudbug.com > wrote:
>"W. Watson" <wolf_tracks@invalid.com> wrote in
>news:P9Lii.442$bz7.357@newssvr22.news.prodigy.net:
>
>> I have this link <http://www.wcrl.ars.usda.gov/cec/java/lat-long.htm>
>> for the topic in the Subject line, but it is broken. Does anyone have
>> one that uses both lat/long of the names of cities to compute the
>> distance?
>
>Simple trig really. COSINE of theta=difference in northings/difference
>in eastings. However for large distances on the earth it becomes"
>COSINE of theta=difference in northings/difference in eastings*(latitude
>factor)
Only works for very small distances. Error gets progressively larger
as distance increases. What you need is spherical trigonometry.
Eugene L Griessel
It is easier to fight for one's principles than to live up to them.
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