Cardinal direction algorithm in Java

Question

This weekend I spend a few minutes thrashing together an algorithm that would take in a heading (in degrees) and return a String for the cardinal direction (I\'m using it in an

Answer 1

The previous examples are not accurate, here is a more accurate solution in JavaScript.

function getCardinalDirection(input) {
    var directions = ["N", "NE", "E", "SE", "S", "SW", "W", "NW", "N"];
    var index = Math.floor( ((input-22.5)%360) / 45 );
    return directions[index+1];
}

Answer 2

That's fine in most cases, though to make it optimized and (IMO) cleaner, what you could do is find a function to relate the input heading to one used in the map.

For example: (I'm pretty sure this is right, but you'll want to check it)

45* (int)Math.round((  ((double)x % 360) / 45))

What this does is first x % 360 makes sure the heading is within a valid range. then

45 * round(.../45)

finds the closest multiple of 45.

Now change your map to be

  HashMap<Integer, String> map = new HashMap<Integer, String>()
  map.put(0, "North")
  map.put(45, "Northeast")
  etc...

So, now your algorithm becomes a fast mathemtical calculation rather than iterating through the map. Furthermore, you don't need as Hashtable here since it provides constructs for concurrency (if I remember correctly) and in your case it would actually cause a performance decrease.

Once again, the performance hit may be completely negligible for your needs.

Edit for Thilo's and shinjin's suggestions:

Instead of multiplying by 45, just keep the rest of the equation, which gives you values for 0-7, and make an array of your strings.

String directions[] = {"N", "NE", "E", "SE", "S", "SW", "W", "NW"}
return directions[ (int)Math.round((  ((double)x % 360) / 45)) % 8 ]

and you've got your problem solved in two lines.

One note: Modulus won't work correctly for negative numbers. If our input heading is negative, you'll need to make it positive first.

Answer 3

Most of the answers here are off by 22.5 degrees for their 45 degree intervals, and map e.g. 0-45 as N, rather than [337.5-360],[0-22.5] to N. You need to offset before doing the math to correct for this.

Here's a solution that uses 22.5 degree intervals, such as you might see for wind directions:

  private String formatBearing(double bearing) {
    if (bearing < 0 && bearing > -180) {
      // Normalize to [0,360]
      bearing = 360.0 + bearing;
    }
    if (bearing > 360 || bearing < -180) {
      return "Unknown";
    }

    String directions[] = {
      "N", "NNE", "NE", "ENE", "E", "ESE", "SE", "SSE",
      "S", "SSW", "SW", "WSW", "W", "WNW", "NW", "NNW",
      "N"};
    String cardinal = directions[(int) Math.floor(((bearing + 11.25) % 360) / 22.5)];
    return cardinal + " (" + formatBearing.format(bearing) + " deg)";
  }

Answer 4

You could maybe add 15 degrees up front to avoid North_1 and North_2.

Answer 5

in java:

String _directions[] = {"N", "NE", "E", "SE", "S", "SW", "W", "NW"};

public String getHeading(int hea) {
  return _directions[(int)Math.floor((hea % 360) / 45)];
}

In "java" case u must need to create a Class.

in javascript:

var _directions = ["N", "NE", "E", "SE", "S", "SW", "W", "NW"];

function getDirection (hea) {
  return _directions[Math.floor((hea % 360) / 45)];
};