Converting wind direction in angles to text words

Question

I have wind direction data coming from a weather vane, and the data is represented in 0 to 359 degrees.

I want to convert this into text format (compass rose) with 16 different directions.

Basically I want to know if there is a fast slick way to scale the angle reading to a 16 string array to print out the correct wind direction without using a bunch of if statements and checking for ranges of angles

Wind direction can be found here.

thanks!

Answer 1

EDIT :

Since there is an angle change at every 22.5 degrees, the direction should swap hands after 11.25 degrees.

Therefore:

349-360//0-11 = N
12-33 = NNE
34-56 = NE

Using values from 327-348 (The entire NNW spectrum) failed to produce a result for eudoxos' answer. After giving it some thought I could not find the flaw in his logic, so i rewrote my own..

def degToCompass(num):
    val=int((num/22.5)+.5)
    arr=["N","NNE","NE","ENE","E","ESE", "SE", "SSE","S","SSW","SW","WSW","W","WNW","NW","NNW"]
    print arr[(val % 16)]

>>> degToCompass(0)
N
>>> degToCompass(180)
S
>>> degToCompass(720)
N
>>> degToCompass(11)
N
>>> 12
12
>>> degToCompass(12)
NNE
>>> degToCompass(33)
NNE
>>> degToCompass(34)
NE

STEPS :

1. Divide the angle by 22.5 because 360deg/16 directions = 22.5deg/direction change.
2. Add .5 so that when you truncate the value you can break the 'tie' between the change threshold.
3. Truncate the value using integer division (so there is no rounding).
4. Directly index into the array and print the value (mod 16).

Answer 2

Here's a javascript implementation of steve-gregory's answer, which works for me.

function degToCompass(num) {
    var val = Math.floor((num / 22.5) + 0.5);
    var arr = ["N", "NNE", "NE", "ENE", "E", "ESE", "SE", "SSE", "S", "SSW", "SW", "WSW", "W", "WNW", "NW", "NNW"];
    return arr[(val % 16)];
}

See his answer for an explanation of the logic.

Answer 3

Watch out for rounding, angles between 349...11 should be "N", therefore add half sector first (+(360/16)/2), then handle overflow over 360 by %360, then divide by 360/16:

["N","NNW",...,"NNE"][((d+(360/16)/2)%360)/(360/16)]

Answer 4

I checked this and it works very good and seems accurate. Source: http://www.themethodology.net/2013/12/how-to-convert-degrees-to-cardinal.html by Adrian Stevens

    public static string DegreesToCardinal(double degrees)
    {
        string[] caridnals = { "N", "NE", "E", "SE", "S", "SW", "W", "NW", "N" };
        return caridnals[(int)Math.Round(((double)degrees % 360) / 45)];
    }

    public static string DegreesToCardinalDetailed(double degrees)
    {
        degrees *= 10;

        string[] caridnals = { "N", "NNE", "NE", "ENE", "E", "ESE", "SE", "SSE", "S", "SSW", "SW", "WSW", "W", "WNW", "NW", "NNW", "N" };
        return caridnals[(int)Math.Round(((double)degrees % 3600) / 225)];
    }

Answer 5

This JavaScript will work for anyone who only needs 8 cardinal directions and would like corresponding arrows.

function getCardinalDirection(angle) {
    const directions = ['↑ N', '↗ NE', '→ E', '↘ SE', '↓ S', '↙ SW', '← W', '↖ NW'];
    return directions[Math.round(angle / 45) % 8];
}

Answer 6

I believe it is easier to:

1. Shift the direction by 11.25
2. Add an "N" at the end of the direction list to handle the 'over 360',

DirTable = ["N","NNE","NE","ENE","E","ESE", "SE","SSE","S","SSW","SW","WSW", "W","WNW","NW","NNW",**"N"**]; 

wind_direction= DirTable[Math.floor((d+11.25)/22.5)];

Answer 7

To do the reverse conversion (compass letter abbreviations to degrees):

function getDir($b)
{

   $dirs = array('N'=>0, 'NNE'=>22.5,"NE"=>45,"ENE"=>67.5, 'E'=>90,'ESE'=>112.5, 'SE'=>135,'SSE'=>157.5, 'S'=>180,'SSW'=>202.5, 'SW'=>225,'WSW'=>247.5, 'W'=>270,'WNW'=>292.5,'NW'=>315,'NNW'=>337.5, 'N'=>0,'North'=>0,'East'=>90,'West'=>270,'South'=>180);
   return $dirs[$b];
}

Answer 8

this works fine

#!/usr/bin/env python

def wind_deg_to_str1(deg):
        if   deg >=  11.25 and deg <  33.75: return 'NNE'
        elif deg >=  33.75 and deg <  56.25: return 'NE'
        elif deg >=  56.25 and deg <  78.75: return 'ENE'
        elif deg >=  78.75 and deg < 101.25: return 'E'
        elif deg >= 101.25 and deg < 123.75: return 'ESE'
        elif deg >= 123.75 and deg < 146.25: return 'SE'
        elif deg >= 146.25 and deg < 168.75: return 'SSE'
        elif deg >= 168.75 and deg < 191.25: return 'S'
        elif deg >= 191.25 and deg < 213.75: return 'SSW'
        elif deg >= 213.75 and deg < 236.25: return 'SW'
        elif deg >= 236.25 and deg < 258.75: return 'WSW'
        elif deg >= 258.75 and deg < 281.25: return 'W'
        elif deg >= 281.25 and deg < 303.75: return 'WNW'
        elif deg >= 303.75 and deg < 326.25: return 'NW'
        elif deg >= 326.25 and deg < 348.75: return 'NNW'
        else: return 'N'

def wind_deg_to_str2(deg):
        arr = ['NNE', 'NE', 'ENE', 'E', 'ESE', 'SE', 'SSE', 'S', 'SSW', 'SW', 'WSW', 'W', 'WNW', 'NW', 'NNW', 'N']
        return arr[int(abs((deg - 11.25) % 360)/ 22.5)]

i = 0
while i < 360:
        s1 = wind_deg_to_str1(i)
        s2 = wind_deg_to_str2(i)
        print '%5.1f deg -> func1(%-3s), func2(%-3s), same:%s' % (i, s1, s2, ('ok' if s1 == s2 else 'different'))
        i += 0.5

Answer 9

If you arrived here and are only interested in breaking your degrees into one of 8 directions.

function degToCompass(num){
    const val =  Math.floor((num / 45) + 0.5);
    const arr = ["N","NE","E", "SE","S","SW","W","NW"];
    return arr[(val % 8)]

Answer 10

I would probably just do simple division of degrees to get a position in an array or an enum value or something that would give you the text you need. Just round down on all your division. 360/16 = 22.5, so you would want to divide by 22.5 to get the position.

String[] a = [N,NNW,NW,WNW,...,NNE]

Answer 11

Javascript function 100% working

function degToCompass(num) { 
    while( num < 0 ) num += 360 ;
    while( num >= 360 ) num -= 360 ; 
    val= Math.round( (num -11.25 ) / 22.5 ) ;
    arr=["N","NNE","NE","ENE","E","ESE", "SE", 
          "SSE","S","SSW","SW","WSW","W","WNW","NW","NNW"] ;
    return arr[ Math.abs(val) ] ;
}

steps

1. Given a 360 degree angle
2. Since north is between -11.25 to 11.25 we subtract 11.25 for accuracy
3. Divide the angle by 22.5 because 360deg/16 directions = 22.5deg/direction change
4. Math.abs for as negative is still north
5. Select the segment from arr from answer

Hope it helps

Answer 12

Here's a one-line python function:

def deg_to_text(deg):
    return ["N","NNE","NE","ENE","E","ESE", "SE", "SSE","S","SSW","SW","WSW","W","WNW","NW","NNW"][round(deg/22.5)%16]

Obviously it can be split into multiple lines for readability/pep8

Answer 13

Used this in Excel: VLOOKUP(MROUND(N12,22.5),N14:O29,2,FALSE)

Cell N12 is direction toward in degrees for which an answer is needed. The range N14:O29 is looking up the sector(A to R):

WIND SECTOR 0 A 22.5 B 45 C 67.5 D 90 E 112.5 F 135 G 157.5 H 180 J 202.5 K 225 L 247.5 M 270 N 292.5 P 315 Q 337.5 R

Answer 14

I use R heavily and needed a solution for this. This is what I came up with and works well for all possible combinations I have fed it:

degToCardinal <- function(degrees) {
  val <- as.integer((degrees / 22.5) + 0.5)
  arr <- c("N","NNE","NE","ENE","E","ESE", "SE", "SSE","S","SSW","SW","WSW","W","WNW","NW","NNW")
  return(arr[((val+1) %% 16)])
}

Answer 15

Wanted to use @eudoxos but needed to pull all the parts together:

def deg_to_compass(d):
  return ["N", "NNE", "NE", "ENE", "E", "ESE", "SE", "SSE",
        "S", "SSW", "SW", "WSW", "W", "WNW", "NW", "NNW"] [math.floor(((d+(360/16)/2)%360)/(360/16))]

Borrrowed @Hristo markow to check the results:

for i in range(0,360):
  print (i,deg_to_compass(i) == wind_deg_to_str2(i))