Calculate destination point given distance and bearing from start point

Jcontreras01 — Wed, 15 Feb 2023 13:14:21 GMT

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?

Re: Calculate destination point given distance and bearing from start point

williambohrmann3 — Thu, 16 Feb 2023 19:14:24 GMT

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.

Re: Calculate destination point given distance and bearing from start point

Jcontreras01 — Mon, 20 Feb 2023 06:21:03 GMT

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

topic Re: Calculate destination point given distance and bearing from start point in .NET Maps SDK Questions

Calculate destination point given distance and bearing from start point

Re: Calculate destination point given distance and bearing from start point

Re: Calculate destination point given distance and bearing from start point