Re: distance from Easter Island to Chile

[Emanuel Berg <embe8573@student.uu.se>]

giacomo.boffi@gmail.com writes:

> (progn (defun d2r (x) (/ (* pi x) 180)) ...

Aha, degrees-to-radians is a macro, won't play with
mapcar (?). Did some improvements (I hope) to the
interface:

(defun d2r (d) (/ (* pi d) 180))

(defun spherical-law-of-cosines (p1 p2)
  (let ((lat1 (car p1)) (lon1 (cadr p1))
        (lat2 (car p2)) (lon2 (cadr p2)))
    (acos (+ (* (sin lat1) (sin lat2))
             (* (cos lat1) (cos lat2) (cos (- lon2 lon1)))))))

(defun distance-2 (p1 p2)
  (let*((from          (car p1))
        (from-coords-r (mapcar 'd2r (cadr p1)))
        (to            (car p2))
        (to-coords-r   (mapcar 'd2r (cadr p2)))
        (dist (* 6378.1
                 (spherical-law-of-cosines from-coords-r
                                           to-coords-r)) ))
    (message (format "%s -> %s: %8.2f km" from to dist)) ))

(setq p1 '("Santiago"      (33.4500  70.6667)))
(setq p2 '("Easter Island" (27.1167 109.3667)))

(distance-2 p1 p2)

Now we just need a database of locations, then we can
really go nuts...

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