Find distance of location to route in Google Maps SDK

Question

I´m developing an iPhone app, and I need some help with this case:

I need to check, if user leave google maps route (GMSPolyline) and if distance from user location to nearest point of route is more than 40 meters -- I need to rebuild route.

I can't find the right algorithm to detect if distance from user to route is more than 40 meters.

I've tried to use this method to find projection of user location (converted to CGPoint by CGPointMake) on route :

+ (CGPoint)projectionOfPoint:(CGPoint)origPoint toSegmentP1:(CGPoint)p1 p2:(CGPoint)p2 {
// for case line is parallel to x axis
if (p2.y == p1.y) {
    return CGPointMake(origPoint.x, p1.y);

// for case line is parallel to y axis
} else if (p2.x == p1.x) {
    return CGPointMake(p1.x, origPoint.y);
}

// line from segment
CGFloat kKoefLine1 = (p2.x - p1.x)/(p2.y - p1.y);
CGFloat bKoefLine1 = p1.y - kKoefLine1*p1.x;

// perpendicular line
CGFloat kKoefLine2 = -1/kKoefLine1;
CGFloat bKoefLine2 = origPoint.y - kKoefLine2*origPoint.x;

// cross point
CGFloat krossX     = (bKoefLine2 - bKoefLine1)/(kKoefLine1 - kKoefLine2);
CGFloat krossY     = kKoefLine2*krossX + bKoefLine2;

return CGPointMake(krossX, krossY);}

Then I calculate distance from returned projection (converted to CLLocation) and user location, but it doesn't works.

P.S.: I will be thankful if solution would be written on swift.

Answer 1

There is a GMSGeometryIsLocationOnPath function in the GMSGeometryUtils module in the Google Maps SDK.

You should be able to use that to calculate what you need.

Pseudocode (not tested):

let currentLocation: CLLocationCoordinate2D = ...
let routePath: GMSPath = routePolyline.path
let geodesic = true
let tolerance: CLLocationDistance = 40

let within40Meters = GMSGeometryIsLocationOnPath(currentLocation, routePath, geodesic, tolerance)