Calculate destination point given distance and bearing from start point

[Jcontreras01]

I'm using .Net Maps SDK for a WPF application.
I need to calculate a destination point given a distance and bearing from another start point.

Now I'm using the following method to calculate the destination point.

public void demo()
        {
            MapPoint startPoint = new MapPoint(-7.123456789, 33.123456789);
            double bearingDegreesFromNorth = 33;
            double distanceMeters = 54321;
            // Firts calculate endPoint using startPoint, distance, and bearing.
            MapPoint endPoint = CalculateCoordinatesWithOffset(startPoint, distanceMeters, 0, bearingDegreesFromNorth);
            // Now with endPoint I calculate again startPoint using the same distance but reverse bearing.
            MapPoint startPointAgain = CalculateCoordinatesWithOffset(endPoint, distanceMeters, 0, bearingDegreesFromNorth + 180);

            // Result endPoint:{MapPoint[X=-6.80405266951967, Y=33.5330337977028]}
            // Result startPointAgain: {MapPoint[X=-7.12195591588525, Y=33.1226432181444]}

        }
public static MapPoint CalculateCoordinatesWithOffset(MapPoint mapPoint, double xOffset, double yOffset, double bearing = 0)
        {
            double distance = Math.Sqrt(Math.Pow(xOffset, 2) + Math.Pow(yOffset, 2));
            // Convert to radians
            double latRad = mapPoint.Y * Math.PI / 180.0;
            double lonRad = mapPoint.X * Math.PI / 180.0;
            double bearingRad = Math.Atan2(yOffset, xOffset) + Conversion.DegToRadians(bearing);
            double s = distance * Math.PI / (180.0 * 60 * 1852);
            // Find the new latitude
            double endLat = Math.Asin(Math.Sin(latRad) * Math.Cos(s) + Math.Cos(latRad) * Math.Sin(s) * Math.Cos(bearingRad));
            // Then the new longitude
            double w = Math.Atan2(Math.Sin(bearingRad) * Math.Sin(s) * Math.Cos(latRad), Math.Cos(s) - Math.Sin(latRad) * Math.Sin(endLat));
            double endLon = lonRad + w;
            endLat = endLat * 180.0 / Math.PI;
            endLon = endLon * 180.0 / Math.PI;
            var result = new MapPoint(endLon, endLat);
            return result;
        }

But when I try to calculate the start point using the same distance and the reverse bearing from the destination point, the start point does not coincide.

In the beginning, startPoint value is (-7.123456789, 33.123456789), but when I recalculated the value is [X=-7.12195591588525, Y=33.1226432181444]
Both points are similar, but the last decimals do not coincide.

What is the best way to do that? Is there any way to calculate a point given distance and bearing from the start point and then use the destination point, with the distance and the reverse bearing (bearing +-180º), to calculate the initial point?

[williambohrmann3 · Accepted solution]

Hello there. I would recommend utilizing the MoveGeodetic method.

public static MapPoint CalculateCoord(MapPoint mapPoint, double distance, GeodeticCurveType curveType, double bearing = 0)
        {
            return GeometryEngine.MoveGeodetic(new List<MapPoint>() { mapPoint }, distance, LinearUnits.Meters, bearing, AngularUnits.Degrees, curveType)[0];
        }

 The mapPoint parameter would need a spatial reference. 

In terms of precision - your bearing changes over long distance. So it isn't as simple as bearing + 180 to go from end point to start point.

[Jcontreras01]

Thanks @williambohrmann3, that work to me using  GeodeticCurveType.Loxodrome.