OK, short answer:
(1) N 39º 19' 16.80205" W 77º 43' 10.14059"
(2) N 39º 19' 16.17539" W 77º 43' 10.75219"
Vincenty inverse algorithm distance results:
24.251 m = 2425.1 cm -> * (1/2.540)in/cm [exact] -> 954.7638 in
954.7638 in * (1/12) ft/in = 79.5636 ft = 79 ft 6.7636 in
"aletheiak"'s online good calculator = 79 ft 6.7695 in
Difference = -0.0059 in
I'm not going to lose sleep over that. :)
I wouldn't trust anyone, other than
the surveyor, claiming more accuracy
or even precision. It could be precise
to umpteen digits and be repeatable,
but still not be accurate.
The full GCGC output is at the bottom, FYI,
so you can see what all you get.
See the line "Input" to see
what the input to GCGC looks like
- as simple and freeform as I could make it.
Most other lat/long formats are accepted.
"Grid" is a ham radio only thing.
"Mag Dec" is the magnetic declination/variation
for the given lat/long, exclusive
of any big local masses of iron.
"Long Path" is not usually of BP concern.
It's the long way around the earth.
GCGC results can be saved to a file
and studied later as was this run.
=========================
Hmmmm...
I now notice a slight difference in the gcb output
from GCGC, 79 ft _9_in. ?
That is no doubt from the lat/long seconds
being rounded off after 3 decimal places on input.
Three are usually way, way more than can be justified,
except for data straight from a surveyor
who can actually measure such things,
as in this case. One decimal digit for seconds
is usually kidding oneself.
Ham radio operators dont usually work
with such small distances
and differences that tiny don't show up.
I _may_ need to tweak the gcb input format
to allow a few more digits for seconds
for really close BP work,
but not a ridiculous amount more.
GCGC accepts lots of input digits
and treats them very carefully and with respect.
The results appear ok compared to the earlier distance.
======================
Before I forget to mention it,
the best great circle calculator online is
<
http://www.indo.com/distance>
He uses the USGS algorithms.
I use the equivalent US NGS versions.
[...PAUSE...]
Hmmmm... I see he rounds off the seconds
to integers and gets a distance of 0 miles.
- OK - NOT the best for _really_ close work
for BP purposes after all. Oh well.
There are a few more calculators,
online and offline, and spreadsheets
that use the Vincenty or Sodano algorithms
that _may_ keep the decimal seconds
(or enough digits for decimal degrees or minutes).
I will have to check my bookmarks and notes
and pass on a recommendation or two
in addition to the good one "aletheiak" uses.
I do regular google searches for such things.
I am usually impressed, but often not favorably.
=============================
The best online tutorial for all of this is
Ed Williams' Aviation Formulary
<
http://williams.best.vwh.net/avform.html>
His calculator is probably one of the good ones.
There will be a quiz.
===========================
I am always happy to run lat/long data
through the toys I've built.
(Please don't throw me in the briar patch.)
The best thing, though, is to make sure BP folks
can play with the toys themselves.
This is on the lines of
"... give a man a fish..." versus
"... teach a man to fish..." :)
Hopefully, folks can find my little programs useful
as more tools in the BP kit.
I've made a quick change in my GCGC and gcb programs
to switch output from kilometers to meters
for distances less than 1 kilometer.
Then one can apply the _exact_ conversion factor
for meters to inches of 1/2.540...0,
then feet to inches of 1/12 (of course).
Building in inches in the code would take
a bit more time than I had last night.
The new versions are posted to my web site.
GCGC and gcb are both DOS programs.
DOS is still easy to run under Windows
and easy to use once one gets used
to a naked command line prompt.
Some brief notes on how to do it are on the web site.
Javascript GUI versions with data windows
radio buttons and drop down menus,... are being worked on,
but it will take a while to join the 21st Century.
There are a lot of lines of code
and some may not translate easily from Fortran 77.
Some things will be much easier.
Future plans/hopes involve map input/output...
"...retractable tape measure level of high tech..."
I measured tiny, weirdly shaped tobacco lots
on the sides of hills for the US Dept. of Agriculture
using a survey chain and drawing little parallelograms
as a summer job after high school.
"...I really trust the surveyor guy implicitly
all the way to the last digit..."
That's usually a good thing.
It wasn't always so. When I was growing up
in sw VA, I heard that the surveyors
who did the VA-NC-TN line got drunk one day
and strayed a bit north.
Kingsport, TN was supposed to have been in VA.
Does anyone have any references or info about that?
Sorry about getting wound up and so long winded.
Some of my favorite hot buttons were touched. :)
Comments, suggestions, and especially corrections
are always welcome.
Cheers, 73,
Ron McC.
w2iol@...
Ronald C. McConnell, PhD
WGS-84: N 40º 46' 57.6" +/-0.1"
W 74º 41' 22.1" +/-0.1"
FN20ps.77GU31 +/-
NAD-27: V +5058.3438 H +1504.2531
http://home.earthlink.net/~rcmcc
There are two secrets to success:
(1) Don't tell all you know.
================================
+++++++ START RUN +++++++++++++++++++++++++++
GCGC = Great Circles, Grid-squares & Coordinates
[V.2004.04, 2004 August 17, w2iol]
Input = -w n 39 19 16.80205 w 77 43 10.14059 n 39 19
16.17539 w 77 43 10.75219
Sta. 1: Grid = FM19dh.37PC88 Mag Dec = 10.5 W deg
N 39d 19m 16.8s = 39d 19.280m = 39.321330d N
W 77d 43m 10.1s = 77d 43.169m = 77.719480d W
Sta. 2: Grid = FM19dh.37PB38 Mag Dec = 10.5 W deg
N 39d 19m 16.2s = 39d 19.270m = 39.321160d N
W 77d 43m 10.8s = 77d 43.179m = 77.719650d W
Short Path: 1-2 = 217.16 deg .015 mi WGS 84
2-1 = 37.16 deg 24.251 m .013 nmi
Long Path: 1-2 = 37.16 deg 24859.701 mi
2-1 = 217.16 deg 40007.810 km 21602.489 nmi
Magnetic: 1-2: Short: 228 deg Long: 48 deg
[2004.63] 2-1: Short: 48 deg Long: 228 deg
========================================
END rcmcc message (finally)
======================