Haversine Calculator
 

On Wed, 08 Oct 2008 15:04:51 GMT, (Richard
Casady) wrote:

On Sun, 05 Oct 2008 14:23:08 -0400, Marty wrote:

Well I found a nice little on-line Haversine (the function to compute
the Great Circle distance between two points) calculator.

I have had good luck with a pair of deviders.

Casady

How do you calculate great circle distances with dividers ?

Haversine Calculator
 

On Oct 8, 10:03*am, Wayne.B wrote:
On Wed, 08 Oct 2008 15:04:51 GMT, (Richard
....
I have had good luck with a pair of deviders.
....
How do you calculate great circle distances with dividers ?

Plot the LL's on a gnomic chart?

--Tom.

Haversine Calculator
 

On Wed, 8 Oct 2008 10:17:50 -0700 (PDT), "
wrote:

On Oct 8, 10:03*am, Wayne.B wrote:
On Wed, 08 Oct 2008 15:04:51 GMT, (Richard
...
I have had good luck with a pair of deviders.
...
How do you calculate great circle distances with dividers ?

Plot the LL's on a gnomic chart?

That might work as a piece-wise approximation.

Haversine Calculator
 

On Oct 8, 9:15*pm, Wayne.B wrote:
On Wed, 8 Oct 2008 10:17:50 -0700 (PDT), "
How do you calculate great circle distances with dividers ?

Plot the LL's on a gnomic chart?

That might work as a piece-wise approximation.

Sorry, I know that wasn't a very helpful idea. Since a straight line
on a gnomic chart is a great circle if you just count the number of
degrees along the line that should provide naut miles. I'm not sure
how helpful dividers would be in measuring those degrees. I'm also
not sure if they make gnomic charts to a scale appropriate for
plotting such short distances. What would be the point?

--Tom.

Haversine Calculator
 

On Thu, 9 Oct 2008 09:01:39 -0700 (PDT), "
wrote:

That might work as a piece-wise approximation.

Sorry, I know that wasn't a very helpful idea. Since a straight line
on a gnomic chart is a great circle if you just count the number of
degrees along the line that should provide naut miles. I'm not sure
how helpful dividers would be in measuring those degrees. I'm also
not sure if they make gnomic charts to a scale appropriate for
plotting such short distances. What would be the point?

Good question since it's so easy to do it computationally. Our
friend Richard Casady claimed he could do it with dividers but I
suspect he hasn't really tried it. The only graphical solution with
dividers that I would have much faith in would be on the surface of a
globe using a taut string. Everything else I can think of would be a
piece-wise approximation using computed way points on a Mercator
chart.

Haversine Calculator
 

On Oct 9, 10:27*am, Wayne.B wrote:
...*The only graphical solution with
dividers that I would have much faith in would be on the surface of a
globe using a taut string. ...

If you have just the right projection it can be done but you'd need a
custom chart which is going to be harder to come by than a
programmable calculator. I haven't been following Skip's path closely
enough to know, but I suppose he was heading near enough to true south
that the rhumb line distance can be taken as the great circle distance
with negligible error.

In a desperate attempt to add some content I want to point out that if
you are going to do sailings calculations by calculator and are
looking to Dutton's (at least up the edition 14) for guidance beware
that the sailing chapter is full of errors large and small. This is a
better source:
http://williams.best.vwh.net/avform.htm

--Tom.

Haversine Calculator
 

On Thu, 9 Oct 2008 11:14:58 -0700 (PDT), "
wrote:

In a desperate attempt to add some content I want to point out that if
you are going to do sailings calculations by calculator and are
looking to Dutton's (at least up the edition 14) for guidance beware
that the sailing chapter is full of errors large and small. This is a
better source:
http://williams.best.vwh.net/avform.htm

Good site, thanks.

I have a Dutton's somewhere but haven't cracked it in years. I think
the Naval Academy used it as a navigation text at one time. :-)

Haversine Calculator
 

On Oct 9, 12:12*pm, Wayne.B wrote:
On Thu, 9 Oct 2008 11:14:58 -0700 (PDT), "
...http://williams.best.vwh.net/avform.htm

Good site, thanks.

I have a Dutton's somewhere but haven't cracked it in years. *I think
the Naval Academy used it as a navigation text at one time. * :-)

You're welcome. Somebody posted it here a while ago. I'm sorry I've
forgotten who, but thanks to them. I have tested most of the
algorithms there and they work.

I worked all the problems in the Sailings chapter in Dutton's because
I wanted to make a Mercator sailings calculator -- GC calcs are a dime
a dozen. I was amazed at how bad the text was. I left the book in
Hawaii but if my memory serves the algorithm they provide for Mercator
sailing is not generalizable and only works in special cases in the
NW. The problem they work is so full of errors that even a casual
glance shows it to be impossible -- they did crib the answer but all
their work is wrong. There were also serious problems with the GC
section. This for a book that is still the navigation text at the USNA
and has gone through 14 editions... Presumably that means no one at
the Academy has bothered to work or even closely read the sailings
problems... ... Dutton's does have really nice illustrations...

--Tom.

--Tom.

Haversine Calculator
 

On Thu, 09 Oct 2008 13:27:55 -0400, Wayne.B
wrote:

On Thu, 9 Oct 2008 09:01:39 -0700 (PDT), "
wrote:

That might work as a piece-wise approximation.

Sorry, I know that wasn't a very helpful idea. Since a straight line
on a gnomic chart is a great circle if you just count the number of
degrees along the line that should provide naut miles. I'm not sure
how helpful dividers would be in measuring those degrees. I'm also
not sure if they make gnomic charts to a scale appropriate for
plotting such short distances. What would be the point?

Good question since it's so easy to do it computationally. Our
friend Richard Casady claimed he could do it with dividers but I
suspect he hasn't really tried it. The only graphical solution with
dividers that I would have much faith in would be on the surface of a
globe using a taut string. Everything else I can think of would be a
piece-wise approximation using computed way points on a Mercator
chart.

You can't possibly think the difference between a 6 mi long rhumb line
and a great circle is of any significant. My uncle navigated a few
million miles with dividers and charts. I have the dividers, two of
them, as a matter of fact. The E6B nav computer has circular slide
rule on one side, on the other a slice of a plotting board, for
solving wind triangles. I have that one, and another he stole and gave
me in 64. There was a sextant built into the plane. You ever hear of a
B-52 getting lost?

Casady

Haversine Calculator
 

On Fri, 10 Oct 2008 01:56:42 GMT, (Richard
Casady) wrote:

You can't possibly think the difference between a 6 mi long rhumb line
and a great circle is of any significant.

It makes a big difference on 3,000 mile east/west passages however,
especially in higher latitudes.