GEOSwift with Google Maps iOS SDK (Draw a polygon)

I am using GEOSwift library (https://github.com/GEOSwift/GEOSwift)

I need help in:

1 - How can I draw polygon geometry data on Google Maps, Here is the code:

let geometry = try! Geometry(wkt: "POLYGON((35 10, 45 45.5, 15 40, 10 20, 35 10))")

2 - How can I get Coordinates (lat, long) from the Geometry (geometry) back in form of string or CLLocationCoordiantes

Thanks ...

Solution

I'll assume you're using Google Maps SDK for iOS version 3.3.0 and GEOSwift version 5.1.0.

You have a polygon (without holes) represented as WKT and you want to show it on a Google Map. Specifically, you probably want to end up with a GMSPolygon

If you know that your WKT will always be a polygon, you can actually write

let polygon = try! Polygon(wkt: "POLYGON((35 10, 45 45.5, 15 40, 10 20, 35 10))")

If you can't guarantee that, you can do what you wrote initially

let geometry = try! Geometry(wkt: "POLYGON((35 10, 45 45.5, 15 40, 10 20, 35 10))")

and then extract the polygon using if case let/guard case let/switch case let:

switch geometry {
case let .polygon(polygon):
    // Do something with polygon
default:
    // handle other types of Geometry or fail here
}

Check the definition of Geometry that shows the other cases you might care to handle.

Once you have polygon: Polygon, you can get the points that represent its exterior:

let points = polygon.exterior.points

Polygon.exterior gives you a Polygon.LinearRing and Polygon.LinearRing.points gives you an array of Point.

Now that you have points, you can map them into an array of CLLocationCoordinate2D

let coords = points.map { p in CLLocationCoordinate2D(latitude: p.y, longitude: p.x) }

Note that y goes with latitude and x goes with longitude.

Now that you have coords, you can create a GMSPath using its mutable subclass, GMSMutablePath:

let path = GMSMutablePath()
for c in coords {
    path.addCoordinate(c)
}

You can use that path to create a GMSPolygon:

let polygon = GMSPolygon(path: path)

Then you just need to add it to you map:

polygon.map = yourMap