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Thanks to George et al for working me through the similarities/differences
of two tangent-based azimuth formulas.

That, and the methods HO229 use to create the tables being digested,
George's post offered another calculator method of determining azimuth that
has stayed under the list radar.

George wrote:

"If a calculator or computer offers a POL or arctan2 function then you don't
even need to apply those rules; the azimuth comes out straightaway in its
correct quadrant, from 0 to 360.

For example, the correct angle results from applying-

POL((tan dec cos lat - cos (hour angle)sin lat, -sin (hour angle)).

Before applying this formula, however, check whether the term before the
comma and the term after the comma do not both happen to be zero. If they
do, the angle is indeterminate, and an error may result."

George

These terms are new to me.  I wonder if they might be the same as or similar
to the rectangular-to-polar and polar-to-rectangular functions on my
TI-30XA?  With the TI-30XA, I enter two figures and get two back.

With those functions I can convert difference in Lat 1 and Lat 2, and Lon 1
and Lon 2 to miles, and properly signed, it will give me course and distance
for short trips (under 300 nm) plenty good enough for a sailing vessel. As
you stated, no rules need to be applied to the course value--unless it is
negative,  then add 360.  The only trick is to enter latitude as the x value
and longitude as the y value to account for the differences in cardinal vs.
trig coordinate systems.  Also can enter course and distance and calculate
Lat and Lon differences from departure point.

If POL and arctan2 are the same as my P to R and  R to P functions, would
you please go into a bit more detail on how to use them with your method?  I
am also confused by the "," after sin lat in your formula.

If not, would love to learn what they are.

Thanks

Bill

Thanks

Bill

   

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