Converting string with polygon coordinates to lat / lng format

Question

I have a string with a list of polygon coordinates in the following format:

var myString = "(38.35870116756209, 38.27089903372614),(38.3339292947434, 38.2743322612652),(38.33944984782068, 38.3017980815777),(38.35829734627614, 38.297678208530826)";

I want to convert that string to an array with lat / lng coordinates, like this:

const polygonCoords = [
    { lat: 38.35870116756209, lng: 38.27089903372614 },
    { lat: 38.3339292947434, lng: 38.2743322612652 },
    { lat: 38.33944984782068, lng: 38.3017980815777 },
    { lat: 38.35829734627614, lng: 38.297678208530826 },
    { lat: 38.35870116756209, lng: 38.27089903372614 } // first coordinate again
];

How can I do this?

Answer 1

IMO the most elegant way to approach this problem, is to...

1. use String.prototype.replaceAll() to convert your string format into a JSON-compatible 2-dimensional array string
2. use JSON.parse() to convert your array string to an actual array
3. use Array.prototype.map() to convert your array to the desired format
4. use Array.prototype.push() to duplicate a reference to the first coordinate and append

Working demo

var myString = "(38.35870116756209, 38.27089903372614),(38.3339292947434, 38.2743322612652),(38.33944984782068, 38.3017980815777),(38.35829734627614, 38.297678208530826)";

// 1. Convert string format to 2-dimensional array
myString = '[' + myString.replaceAll('(', '[').replaceAll(')', ']') + ']';

// 2. Parse array
const myArray = JSON.parse(myString);

// 3. Convert array format to polygonCoords
const polygonCoords = myArray.map(v => ({lat: v[0], lng: v[1]}));

// 4. Duplicate reference to first coordinate and append
polygonCoords.push(polygonCoords[0]);

console.log("OUTPUT :");
console.log(polygonCoords);
console.log("NUMBER OF COORDINATES :");
console.log(polygonCoords.length);

Or, if you prefer minimal code over readability, you can combine the first 3 statements, like this :

var myString = "(38.35870116756209, 38.27089903372614),(38.3339292947434, 38.2743322612652),(38.33944984782068, 38.3017980815777),(38.35829734627614, 38.297678208530826)";

// Convert string to polygonCoords
const polygonCoords = JSON.parse('[' + myString.replaceAll('(', '[').replaceAll(')', ']') + ']')
                          .map(v => ({lat: v[0], lng: v[1]}));
// Duplicate reference to first coordinate and append
polygonCoords.push(polygonCoords[0]);

console.log("OUTPUT :");
console.log(polygonCoords);
console.log("NUMBER OF COORDINATES :");
console.log(polygonCoords.length);

Note

polygonCoords.push(polygonCoords[0]) does not actually duplicate the first coordinate object itself. Instead it copies a reference to the same object. So, if you change the values of coordinate polygonCoords[0], you also change the values of coordinate polygonCoords[length-1] and vice versa. Considering these should always be identical in polygons, I favor this approach.

If you nonetheless want to duplicate the object itself rather than a reference to the object, you will need to clone it first. To do this, use polygonCoords.push(Object.assign({}, polygonCoords[0])); instead of polygonCoords.push(polygonCoords[0]).