Merge pull request #10 from jleh/latlng-to-locator

Convert coordinates to locator string.

Author: jleh

README.md

@@ -5,12 +5,12 @@ Operations with [Maidenhead locator system](https://en.wikipedia.org/wiki/Maiden
 ## Usage
 
 ```javascript
-const { locatorToLatLng, distance } = require('qth-locator');
+const { locatorToLatLng, distance, bearingDistance, latLngToLocator } = require('qth-locator');
 
 locatorToLatLng('IO91wm'); // [51.521, -0.125]
 distance('IO91wm', 'KP20le'); // 1821.5 km
 bearingDistance('FN20qr', 'KP21ol') // 6586.72 km, 49.16 degrees
-
+latLngToLocator(60.179, 24.945) // KP21le
 ```
 
 ## License

package.json

@@ -1,6 +1,6 @@
 {
   "name": "qth-locator",
-  "version": "2.0.0",
+  "version": "2.1.0",
   "description": "Maidenhead locator calculator",
   "repository": {
     "type": "git",

src/index.js

@@ -6,6 +6,7 @@ const CHAR_CODE_OFFSET = 65;
 const isValidLocatorString = locatorString => locatorString.match(/^[A-Ra-r][A-Ra-r]\d\d[A-Xa-x][A-Xa-x]/) !== null;
 
 const charToNumber = char => char.toUpperCase().charCodeAt(0) - CHAR_CODE_OFFSET;
+const numberToChar = number => String.fromCharCode(number + CHAR_CODE_OFFSET);
 
 const locatorToLatLng = (locatorString) => {
   locatorString += 'll'; // append subsquare in case is 4 chars long...  If not, is ignored.
@@ -56,9 +57,34 @@ const bearingDistance = (from, to) => {
 
 const distance = (from, to) => bearingDistance(from, to).km;
 
+const isValidPoint = (lat, lng) => (lat >= -90 && lat <= 90) && (lng >= -180 && lng <= 180);
+
+const latLngToLocator = (lat, lng) => {
+  if (!isValidPoint(lat, lng)) {
+    throw new Error('Input is not a valid coordinate');
+  }
+
+  const longitude = lng + 180;
+  const latitude = lat + 90;
+
+  const squareLng = numberToChar(Math.floor(longitude / 20));
+  const squareLat = numberToChar(Math.floor(latitude / 10));
+
+  const fieldLng = Math.floor(longitude % 20 / 2);
+  const fieldLat = Math.floor(latitude % 10);
+
+  const subsquareLng = numberToChar(Math.floor((longitude % 20 % 2) * 12)).toLowerCase();
+  const subsquareLat = numberToChar((latitude % 10 - fieldLat) * 24).toLowerCase();
+
+  return squareLng + squareLat
+    + fieldLng + fieldLat
+    + subsquareLng + subsquareLat;
+};
+
 module.exports = {
-  isValidLocatorString: isValidLocatorString,
-  locatorToLatLng: locatorToLatLng,
-  distance: distance,
-  bearingDistance: bearingDistance
+  isValidLocatorString,
+  locatorToLatLng,
+  distance,
+  bearingDistance,
+  latLngToLocator
 };

test/index.spec.js

@@ -21,16 +21,9 @@ describe('QTH locator', () => {
     expect(BDPair.deg).toBeCloseTo(deg);
   };
 
-  const expectInvalifGridErr = (fn, a, b) => {
-    expect.assertions(2);
-
-    try {
-      fn(a, b);
-    } catch (error) {
-      expect(error).toHaveProperty('message', 'Input is not valid locator string');
-      expect(error).toBeInstanceOf(Error);
-    }
-  };
+  const expectInvalidGridErr = fn => expect(fn).toThrow('Input is not valid locator string');
+
+  const expectInvalidLatLngErr = fn => expect(fn).toThrow('Input is not a valid coordinate');
 
   it('Converts locator string to coordinates', () => {
     expectCoordinates(qthLocator.locatorToLatLng('KP20le'), 60.188, 24.958);
@@ -55,18 +48,33 @@ describe('QTH locator', () => {
   });
 
   it('Detect invalid grid', () => {
-    expectInvalifGridErr(qthLocator.locatorToLatLng, 'RZ73');
+    expectInvalidGridErr(() => qthLocator.locatorToLatLng('RZ73'));
   });
 
   it('Locate debatable grid - It is in spec!', () => {
     expectCoordinates(qthLocator.locatorToLatLng('RR73'), 83.479, 174.96);
   });
 
   it('Detect short grid', () => {
-    expectInvalifGridErr(qthLocator.locatorToLatLng, 'R73');
+    expectInvalidGridErr(() => qthLocator.locatorToLatLng('R73'));
   });
 
   it('detect invalid grid in bearingDistance 1', () => {
-    expectInvalifGridErr(qthLocator.bearingDistance, 'FN20qr', 'F030ll');
+    expectInvalidGridErr(() => qthLocator.bearingDistance('FN20qr', 'F030ll'));
+  });
+
+  it('Converts latLng to grid', () => {
+    expect(qthLocator.latLngToLocator(14.3125, -32.125)).toBe('HK34wh');
+    expect(qthLocator.latLngToLocator(60.179, 24.945)).toBe('KP20le');
+    expect(qthLocator.latLngToLocator(-33.886048, 151.193546)).toBe('QF56oc');
+    expect(qthLocator.latLngToLocator(-22.904788, -43.184915)).toBe('GG87jc');
+  });
+
+  it('Throws error for invalid coordinates', () => {
+    expectInvalidLatLngErr(() => qthLocator.latLngToLocator(91, 120));
+    expectInvalidLatLngErr(() => qthLocator.latLngToLocator(-91, 120));
+    expectInvalidLatLngErr(() => qthLocator.latLngToLocator(55, 181));
+    expectInvalidLatLngErr(() => qthLocator.latLngToLocator(55, -181));
+    expectInvalidLatLngErr(() => qthLocator.latLngToLocator(-91, -181));
   });
 });