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Programming-Idioms

  • Lisp
  • Pascal

Idiom #365 Convert an angle to a direction

Convert a degree, x, of 360, to a Compass direction, y.

For example, 123.4 deg is "South-east".

type
  TDir = (N, NE, E, SE, S, SW, W, NW);
const
  Dirs: array[TDir] of string = ('North','North East','East','South East','South','South West','West','North West');

var
  y: double;
  x: string;
begin
  ...
  y := Dirs[TDir(Round(((x-22.5)/45) + 0.5) mod 8)]);
end.

N: -22.5 to +22.5
NE: 22.5 to 67.5
E: 67.5 to 112.5
SE: 112.5 to 157.5
S: 157.5 to 202.5
SW: 202.5 to 247.5
W: 247.5 to 292.5
NW: 292.5 to 337.5
enum Point {
    N, NE, E, SE, S, SW, W, NW;
    static Point parse(double x) {
        int i = (int) ((x / 45) + .5);
        return values()[i % 8];
    }
}
String y = Point.parse(x).name();

Note, add 0.5 since North also accounts for x > 337.5.
New implementation...
< > ⌨
reilas 
type
  TDir = (N, NE, E, SE, S, SW, W, NW);
const
  Dirs: array[TDir] of string = ('North','North East','East','South East','South','South West','West','North West');

var
  y: double;
  x: string;
begin
  ...
  y := Dirs[TDir(Round(((x-22.5)/45) + 0.5) mod 8)]);
end.
enum Point {
    N, NE, E, SE, S, SW, W, NW;
    static Point parse(double x) {
        int i = (int) ((x / 45) + .5);
        return values()[i % 8];
    }
}
String y = Point.parse(x).name();
y = 'NESW'[int((x / 90) + .5) % 4]
y = ["N", "NE", "E", "SE", "S", "SW", "W", "NW"][int((x / 45) + 0.5) % 8]
winds = %w(N NNE NE ENE E ESE SE SSE S SSW SW WSW W WNW NW NNW)
wind_count = winds.size
y = winds[ x * wind_count / 360.0 + 0.5 % wind_count ]