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Hi there
For what it's worth, reckon have improved that program.
Same output, but in a "purer" way.
Separated the computation from the human-readable presentation.
Have
"abs-degdeci-to-abs-deg-min-sec"
fn. returning a list comprising the numeric Degrees, the Minutes and
the Seconds.
eg. (123 45 67.8) == 123Deg 45Seconds 67.8Seconds
{"Lisp" == "List processing" - so fundamentally right to return a list}
So that output could be used by any calling function for any other
purpose as yet unforeseen.
Test example:
(abs-degdeci-to-abs-deg-min-sec 123.456789)
;; (123 27 24.440400000002)
ie. that fn. has become a general-purpose function for converting
Deg-decimal to Degrees-Minutes-Seconds, "agnostic" to
end-application.
With all conversion to human-readable output for nautical purposes
isolated in the inherently nautical "top-level" user-interaction
calling function
"lat-long-degdeci-to-dms"
I discovered the neat "nth" function in emacs lisp.
Apparently it's written into the interpretter in "C" so very fast.
(car llat) has the same effect as (nth 0 llat)
Damn' thing is, with no "Gee-whizz this is a great new language!!"
there isn't as far as I know the books showing how to apply this
established language (?)
As std. with Lisp, you start out with the bottom-most "cutting-tip"
function and work your way to the user-level function.
(opposite order to "top down" "usual" programming)
---------------- listing ----------------
;;; When copying-and-pasting "Google Maps" degdeci lat. and long.,
;;; delete the comma between the values !!!
(defun abs-degdeci-to-abs-deg-min-sec (absdegdeci)
"Deg-decimal to DMS format output - return list
For navigation this can be called for N-S and W-E, so cannot know what
to call the returned value"
(if (minusp absdegdeci)
"error - cannot handle negative arguments"
(let ((decix60 (* (mod absdegdeci 1) 60)))
(list (truncate absdegdeci) (truncate decix60) (* (mod decix60 1) 60)))))
(defun lat-long-degdeci-to-dms (latdeci longdeci)
(let
((llat (abs-degdeci-to-abs-deg-min-sec (abs latdeci)))
(llong (abs-degdeci-to-abs-deg-min-sec (abs longdeci))))
(format "%03dd %02d' %04.1f'' %s %03dd %02d' %04.1f'' %s"
(car llat)(nth 1 llat)(nth 2 llat)(if (minusp latdeci) 'S 'N)
(car llong)(nth 1 llong)(nth 2 llong)(if (minusp longdeci) 'W 'E))))
---------------- example ----------------
;;; Berry Head lighthouse
;;; Google :
;;; 50.39954886056384, -3.483553379652956
(lat-long-degdeci-to-dms 50.39954886056384 -3.483553379652956)
;; "050d 23' 58.4'' N 003d 29' 00.8'' W"
;;; "paste"
;;; 050 23' 58.4" N 003 29' 00.8" W
;;; into Google Maps gets you back to Berry Head lighthouse
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