Crs.PointAlongRay2d Method
The result of going a given distance from a start point in a given direction.
PointAlongRay2d(Point start, System.Double azimuth, System.Double distance, LineType rayType)
The result of going a given distance from a start point in a given direction.Syntax
public Point PointAlongRay2d (
Point start,
System.Double azimuth,
System.Double distance,
LineType rayType
)Parameters
The starting point, expressed in Crs coordinates.
The starting azimuth, degrees clockwise from true north.
The distance to go, in meters.
Return Value
The point where you end up.
Remarks
If you begin at the start point with the given azimuth, and you go the specified distance in meters - along either a great circle or a rhumb line - you will end up at the returned point. The distance is horizontal and computed at sea level, but the z-value of the returned point will be the same as for the from point.
If the ray follows a great circle, this is known as the first or principal (or forward) geodetic problem.
Line type and accuracy
The possible line types are GreatCircle, GreatCircleApprox and RhumbLine. However, if the projection is non-georeferenced, then the line segment is regarded as a straight line in the plane with north up, giving unknown accuracy on Earth. Otherwise, the from point is unprojected to LongLat, then the end point is computed on the ellipsoid surface, and it is finally projected and returned. The error bounds below do not include errors that may be caused by UnprojectToLongLat and ProjectFromLongLat.
RhumbLine
The ray is a curve of constant azimuth, known as a rhumb line or loxodrome. The Earth is modelled as an ellipsoid, and the method has submillimeter accuracy, except near the poles (latitude above 89.98°), where rhumb lines are useless anyway.
Every rhumb line, when extended, will eventually spiral into a pole (except for rhumb lines that are meridians or parallel circles). The curve length to the pole is finite, but since the spiral makes infinitely many revolutions, it lacks a well-defined direction at the pole, and cannot be continued across it. So, if this method gets a distance longer than the rhumb line can be extended, the corresponding pole is returned.
GreatCircle
The ray is a great-circle segment, also known as a shortest route or geodesic route. The Earth is modelled as an ellipsoid, and the method has submillimeter accuracy.
GreatCircleApprox
The ray is a great-circle segment. But the Earth is modelled as a sphere, with a local compensation used for the flattening of the earth, which means that the accuracy is best over short distances. The following error bounds hold:
distance up to | max error |
|---|---|
100 km | 0.003 % (3 m) |
300 km | 0.008 % (24 m) |
1 000 km | 0.03 % (300 m) |
3 000 km | 0.08 % (3 km) |
10 000 km | 0.22 % (22 km) |
unlimited | 0.26 % (50 km) |
(The percent values are the displacement of the returned point, as a percentage of the given distance.)
Speed
If the projection is already LongLat, then the computation time for GreatCircle will normally be about 1.7 times longer than for GreatCircleApprox.
Platforms
Windows, Linux, Android