Great circle formulae, True cource and actual heading

Hi,

I am trying to write a formula to compute flight headings.
If i use 2 lat/lon i can get a "true course" but due to magnetic variations
the true course is not really all that useful, (knowing that my true course
is 118deg will not tell me that i should fly 93 deg).

What i mean is if i go from A to B i can calculate the True course, ('tc')
but my actual heading varies a lot depending on my position along the
course.

Is there a reliable formula to calculate my actual heading at a certain
point along the course?

Many thanks in advance.

Sims

"Sims" wrote in
:

Hi,

I am trying to write a formula to compute flight headings.
If i use 2 lat/lon i can get a "true course" but due to magnetic
variations the true course is not really all that useful, (knowing
that my true course is 118deg will not tell me that i should fly 93
deg).

What i mean is if i go from A to B i can calculate the True course,
('tc') but my actual heading varies a lot depending on my position
along the course.

Is there a reliable formula to calculate my actual heading at a
certain point along the course?

Many thanks in advance.

Sims

At least in sci.geo.satellite-nav this sort of question about
formulae has been asked numerous times, including quite recent
threads, so a search via Google Groups would likely have already
found you your answer.

Take a look at Ed Williams page about Aviation Formulary:
http://williams.best.vwh.net/avform.htm

--
Dave Patton
Canadian Coordinator, the Degree Confluence Project
http://www.confluence.org dpatton at confluence dot org
My website: http://members.shaw.ca/davepatton/
Vancouver/Whistler - host of the 2010 Winter Olympics

Sims wrote:

Hi,

I am trying to write a formula to compute flight headings.
If i use 2 lat/lon i can get a "true course" but due to magnetic variations
the true course is not really all that useful, (knowing that my true course
is 118deg will not tell me that i should fly 93 deg).

What i mean is if i go from A to B i can calculate the True course, ('tc')
but my actual heading varies a lot depending on my position along the
course.

Is there a reliable formula to calculate my actual heading at a certain
point along the course?

Many thanks in advance.

Sims



You mean your magnetic heading. You have your actual heading. You need
a table of magnetic variations and interprolate from the table based on
your location as there is no mathmatical model that will provide this
information reliably.

Dale
--
_ _ Dale DePriest
/`) _ // http://users.cwnet.com/dalede
o/_/ (_(_X_(` For GPS and GPS/PDAs

Dale DePriest wrote:

You need
a table of magnetic variations and interprolate from the table based on
your location as there is no mathmatical model that will provide this
information reliably.

Given a table of magnetic variations at known locations, there are
statistical methods to derive a useful mathematical model. The web site
cited in a previous article provides such a model as a polynomial.

http://williams.best.vwh.net/avform.htm#Var

In article ,
Craig Prouse wrote:
Dale DePriest wrote:

You need
a table of magnetic variations and interprolate from the table based on
your location as there is no mathmatical model that will provide this
information reliably.

Given a table of magnetic variations at known locations, there are
statistical methods to derive a useful mathematical model. The web site
cited in a previous article provides such a model as a polynomial.

http://williams.best.vwh.net/avform.htm#Var

http://geomag.usgs.gov/chartsdo.html

http://geomag.usgs.gov/models.html

http://www.ngdc.noaa.gov/IAGA/wg8/igrf.html

http://www.ngdc.noaa.gov/IAGA/wg8/table1.txt

http://www.freewarepalm.com/calculator/magcalc.shtml

http://www.garmin.com/manuals/GPSIII...nersManual.pdf page 78 (in document)
(page 88 in pdf file) gives 4 heading adjustment choices: auto magnetic
(using a magnetic field model driven by the current location), true, grid
(driven the UTM locatin) or user magnetic (the user states the desired
adjustment). I suppose that you could use this to include a wind adjustment?!

Other than that; get your aviation weather report and your E6B.

Randolph J. Herber, , +1 630 840 2966, CD/CDFTF PK-149F,
Mail Stop 318, Fermilab, Kirk & Pine Rds., PO Box 500, Batavia, IL 60510-0500,
USA. (Speaking for myself and not for US, US DOE, FNAL nor URA.) (Product,
trade, or service marks herein belong to their respective owners.)

"Dale DePriest" wrote in message


You mean your magnetic heading. You have your actual heading. You need
a table of magnetic variations and interprolate from the table based on
your location as there is no mathmatical model that will provide this
information reliably.


I found the post a little confusing because it seemed to be mixing
the problem of the course heading changing due to the great circle
route (mentioned in the subject) with heading changes due to changing
declination mentioned in the body. Two very different issues.

Steve

red rover wrote:

"Dale DePriest" wrote in message

You mean your magnetic heading. You have your actual heading. You need
a table of magnetic variations and interprolate from the table based on
your location as there is no mathmatical model that will provide this
information reliably.



I found the post a little confusing because it seemed to be mixing
the problem of the course heading changing due to the great circle
route (mentioned in the subject) with heading changes due to changing
declination mentioned in the body. Two very different issues.

Steve

Yes, it was my mistake, I misread the original post by not comparing the
text to the subject line. I tried to cancel but too late, Sorry

Dale


--
_ _ Dale DePriest
/`) _ // http://users.cwnet.com/dalede
o/_/ (_(_X_(` For GPS and GPS/PDAs

"Dale DePriest" wrote in message
...

Yes, it was my mistake, I misread the original post by not comparing the
text to the subject line. I tried to cancel but too late, Sorry

Dale

Well I actually meant the original post was confusing, not your
reply.

"red rover" wrote in message
.. .

"Dale DePriest" wrote in message


You mean your magnetic heading. You have your actual heading. You need
a table of magnetic variations and interprolate from the table based on
your location as there is no mathmatical model that will provide this
information reliably.


(Sorry to reply here your post was cancelled).

Yes i do mean the magnetic heading.
Sorry I was not clear.

Where can i get a table to compute my magnetic heading?

Thanks

Sims.

Sims wrote:

"red rover" wrote in message
.. .

"Dale DePriest" wrote in message

You mean your magnetic heading. You have your actual heading. You need
a table of magnetic variations and interprolate from the table based on
your location as there is no mathmatical model that will provide this
information reliably.


(Sorry to reply here your post was cancelled).

Yes i do mean the magnetic heading.
Sorry I was not clear.

Where can i get a table to compute my magnetic heading?

Try here for a start.

http://www.ngdc.noaa.gov/seg/WMM/DoDWMM.shtml

Dale


Thanks

Sims.



--
_ _ Dale DePriest
/`) _ // http://users.cwnet.com/dalede
o/_/ (_(_X_(` For GPS and GPS/PDAs