TopBand: Re: DBGRID

[Earl W Cunningham]

Hi, Jo,

You wrote:
"I'm just curious what is the distance (in km) of earth's great circle
(i.e from-and-to my grid location in earth circle? Can we calculate it
with DBGRID?"
=====
If you mean the total distance around the Earth, it depends on which
direction you go.

The Earth's polar circumference is 40007.86292 km.  Its equatorial
circumference is 40075.01669 km.

If you go due north (or south) from your QTH, the distance traveled would
be 40007.86292 km (the polar circumference) when you return to the same
point as where you started.

If your QTH was on the equator and you went due east (or west) the
distance would be 40075.01669 km (the equatorial circumference).  But you
are not on the equator, so the only distance easily found is the distance
over the poles.

DBGRID will only find short path distances, i.e., distances that are less
than half of the distance around the Earth in any direction.  At exactly
half-way distances, due to the mathematical problem that we cannot divide
anything by zero, the program will say, "cannot compute antipodal
distances!"

You can find the distance around the Earth at different heading angles,
but with difficultly, by going in increments of, say, 90 degrees (approx
1/4) of the distance at a time.  The dificult part is that the 2nd
increment (after the 1st 90 degrees) must start at the angle that the 1st
increment ended.

Sorry I missed you in the Stew Perry.  Apparently condx were a bit better
at the start of the contest, but my sunrise was at 1458Z so I did'nt
start until 0100Z (after my sunset) to avoid breaking the 14-hour rule.

73, happy new year, de Earl, K6SE


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