first commit

public/js/vendor/gktowgs.js

@@ -0,0 +1,66 @@
+const proj4 = require('proj4')
+const epsg = require('epsg')
+const isObject = require('lodash.isobject')
+const isNumber = require('lodash.isnumber')
+
+const epsgFromZone = (zone) => 'EPSG:'+(31464+zone) // zone 2 = 31466, zone 5 = 31469
+
+const toWGS = (coordinates) => {
+    if(!isObject(coordinates) || !isNumber(coordinates.x) || !isNumber(coordinates.y)){
+        throw new Error('missing or invalid parameter `coordinates`')
+    }
+    if(coordinates.x < 0 || coordinates.x >= Math.pow(10, 7)){
+        throw new Error('`coordinates.x` out of bounds')
+    }
+    if(coordinates.y < 0 || coordinates.y >= Math.pow(10, 7)){
+        throw new Error('`coordinates.y` out of bounds')
+    }
+
+    const zone = +(coordinates.x+'')[0]
+
+    const projected = proj4.default(epsg[epsgFromZone(zone)], 'WGS84', Object.assign({}, coordinates))
+    return ({
+        longitude: projected.x,
+        latitude: projected.y
+    })
+}
+
+const toGK = (coordinates, zone) => {
+    if(!isObject(coordinates) || !isNumber(coordinates.longitude) || !isNumber(coordinates.latitude)){
+        throw new Error('missing or invalid parameter `coordinates`')
+    }
+    if(coordinates.longitude < -180 || coordinates.longitude > 180){
+        throw new Error('`coordinates.longitude` out of bounds')
+    }
+    if(coordinates.latitude < -360 || coordinates.latitude > 360){
+        throw new Error('`coordinates.latitude` out of bounds')
+    }
+
+    if(zone){
+        if(!isNumber(zone)){
+            throw new Error('`zone` parameter must be a number')
+        }
+        if(![2,3,4,5].includes(zone)){
+            throw new Error('if set, `zone` parameter must be one of 2, 3, 4, 5')
+        }
+    }
+    else{
+        zone = Math.floor((+coordinates.longitude + 1.5) / 3)
+        if(![2,3,4,5].includes(zone)){
+            throw new Error('could not detect valid zone (2, 3, 4, 5) from input coordinates')
+        }
+    }
+
+    const proj4coordinates = {
+        x: coordinates.longitude,
+        y: coordinates.latitude
+    }
+
+    const projected = proj4('WGS84', epsg[epsgFromZone(zone)], proj4coordinates)
+    return ({
+        x: projected.x,
+        y: projected.y
+    })
+}
+
+module.exports = {toWGS, toGK}