32 lines
1.2 KiB
OCaml
32 lines
1.2 KiB
OCaml
(* Preamble -- some math, and an "angle" type which might be part of a common library. *)
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let pi = 4. *. atan 1.
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let radians_of_degrees = ( *. ) (pi /. 180.)
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let haversin theta = 0.5 *. (1. -. cos theta)
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(* The angle type can track radians or degrees, which I'll use for automatic conversion. *)
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type angle = Deg of float | Rad of float
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let as_radians = function
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| Deg d -> radians_of_degrees d
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| Rad r -> r
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(* Demonstrating use of a module, and record type. *)
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module LatLong = struct
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type t = { lat: float; lng: float }
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let of_angles lat lng = { lat = as_radians lat; lng = as_radians lng }
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let sub a b = { lat = a.lat-.b.lat; lng = a.lng-.b.lng }
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let dist radius a b =
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let d = sub b a in
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let h = haversin d.lat +. haversin d.lng *. cos a.lat *. cos b.lat in
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2. *. radius *. asin (sqrt h)
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end
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(* Now we can use the LatLong module to construct coordinates and calculate
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* great-circle distances.
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* NOTE radius and resulting distance are in the same measure, and units could
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* be tracked for this too... but who uses miles? ;) *)
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let earth_dist = LatLong.dist 6372.8
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and bna = LatLong.of_angles (Deg 36.12) (Deg (-86.67))
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and lax = LatLong.of_angles (Deg 33.94) (Deg (-118.4))
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in
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earth_dist bna lax;;
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