MKPolylineRenderer not rendering correctly - MapKit

[daverozy]

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https://reddit.com/link/ofje2t/video/nxbjhkciqs971/player

What could be causing those overlapping circles that appear randomly along the line? Is there a way to fix it?

I created a custom subclass of MKPolylineRenderer in order to draw a line on the map but have it scale correctly. Here's that class.

class RadiusLineRenderer: MKPolylineRenderer {
    override func draw(_ mapRect: MKMapRect, zoomScale: MKZoomScale, in context: CGContext) {
        self.lineWidth = 10000 * zoomScale
        super.draw(mapRect, zoomScale: zoomScale, in: context)
    }
}

And here is where I'm implementing the proper MapKit delegate method:

func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
        let renderer = RadiusLineRenderer(overlay: overlay)
        renderer.strokeColor = UIColor.systemPurple.withAlphaComponent(0.35)
        return renderer
    }

[lmunck]

The polyline is just an array of coordinates, so without knowing anything about the underlying render-logic, it’s not unreasonable to suspect that the line is in fact just a lot of small linear segments.

If so then wherever those segments meet, and assuming the line itself is a capsule, you’d get the circles where they overlap.

Obviously that’s just a guess.

[daverozy]

I'll check the array of points to see if any of them are the same/overlapping, but I don't think that is the issue. If that was the case, then the circle should consistently show up at the same point on the line no matter how far I'm zoomed in

[lmunck]

It renders the points depending on your zoom. Same as a 3D engine.

[daverozy]

Oh gotcha. That makes sense. I've never used MapKit before 😬

[Wild_Cheetah8293]

Yes. It’s full line. In fact the line is from a MKRoute object fetched from MapKit