How can I draw a line from a point on a SceneView using a Bearing and Distance?

[alionthego]

I want to draw out a Great Circle radial from a point  on the Earth's Surface using the initial point and a Bearing Distance.  The line will be greater than 500 KM.

Currently I am using the following:

func drawRadialFromPoint(_ point: Point, heading: Double, distance: Double) {

     let overlay = GraphicsOverlay()

     let endPoint = calculateEndPoint(from: point, heading: heading, distance: distance)

     let polyline = Polyline(

        points: [

            point,

            endPoint

        ]

    )

    let polylineSymbol = SimpleLineSymbol(style: .solid, color: .blue, width: 3.0)

    let polylineGraphic = Graphic(geometry: polyline, symbol: polylineSymbol)

    overlay.addGraphic(polylineGraphic)

}

func calculateEndPoint(from startPoint: Point, heading: Double, distance: Double) -> Point {

    let angleInRadians = heading * .pi / 180

    let x = startPoint.x + distance * sin(angleInRadians)

    let y = startPoint.y + distance * cos(angleInRadians)

    return Point(x: x, y: y, spatialReference: startPoint.spatialReference)

}

It seems to work but there are two problems.  I don't believe this method is accurate for long distances on the Earth and I was hoping the API would offer a more accurate method to achieve this.

Secondly, when the user pans the earth and the start point is no longer visible, the line disappears which is a problem.

Is there a better way to achieve this?  

[Ting · Accepted solution]

> I don't believe this method is accurate for long distances on the Earth and I was hoping the API would offer a more accurate method to achieve this.

Please check out the geodeticMove(_:distance:distanceUnit:azimuth:azimuthUnit:curveType:) in the API. It allows you to move a point in a geodesic manner for a distance and a bearing (azimuth), and also allows you to specify one of the geodesic curve types.

Here is a small demo I wrote for a different purpose using the old SDK, but it shows how to draw a line given the starting point and the distance and azimuth. Please let me know if you need more info.

> when the user pans the earth and the start point is no longer visible, the line disappears which is a problem.

The point and line graphics should only disappear when they are outside the field of view of a scene view. Please see the attached video. Is it what you are seeing?

[alionthego]

Thanks.  This is really great and draws the line nicely.  I will read up on difference between the curveTypes geodesic and greatElliptical