Class Sky


  • public class Sky
    extends java.lang.Object
    Functions useful for working with shapes on a sphere. All angles are expressed in degrees.
    Since:
    13 Feb 2019
    Author:
    Mark Taylor
    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method Description
      static boolean inSkyPolygon​(double lon0, double lat0, double... lonLats)
      Tests whether a given sky position is inside the polygon defined by a given set of vertices.
      static double midLat​(double lat1, double lat2)
      Determines the latitude midway between two given latitudes.
      static double midLon​(double lon1, double lon2)
      Determines the longitude mid-way between two given longitudes.
      static double skyDistance​(double lon1, double lat1, double lon2, double lat2)
      Calculates the separation (distance around a great circle) of two points on the sky in degrees.
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Method Detail

      • skyDistance

        public static double skyDistance​(double lon1,
                                         double lat1,
                                         double lon2,
                                         double lat2)
        Calculates the separation (distance around a great circle) of two points on the sky in degrees.

        This function is identical to skyDistanceDegrees in class CoordsDegrees.

        Parameters:
        lon1 - point 1 longitude in degrees
        lat1 - point 1 latitude in degrees
        lon2 - point 2 longitude in degrees
        lat2 - point 2 latitude in degrees
        Returns:
        angular distance between point 1 and point 2 in degrees
      • midLon

        public static double midLon​(double lon1,
                                    double lon2)
        Determines the longitude mid-way between two given longitudes. In most cases this is just the mean of the two values, but this function copes correctly with the case where the given values straddle the lon=0 line.
        Parameters:
        lon1 - first longitude in degrees
        lon2 - second longitude in degrees
        Returns:
        longitude midway between the given values
        Examples:
        midLon(204.0, 203.5) = 203.75, midLon(2, 359) = 0.5
      • midLat

        public static double midLat​(double lat1,
                                    double lat2)
        Determines the latitude midway between two given latitudes. This simply returns the mean of the two values, but is supplied for convenience to use alongside the midLon function.
        Parameters:
        lat1 - first latitude in degrees
        lat2 - second latitude in degrees
        Returns:
        latitude midway between the given values
        Examples:
        midLat(23.5, 24.0) = 23.75
      • inSkyPolygon

        public static boolean inSkyPolygon​(double lon0,
                                           double lat0,
                                           double... lonLats)
        Tests whether a given sky position is inside the polygon defined by a given set of vertices. The bounding lines of the polygon are the minor arcs of great circles between adjacent vertices, with an extra line assumed between the first and last supplied vertex. The interior of the polygon is defined to be the smaller of the two regions separated by the boundary. The vertices are specified as a sequence of loni, lati pairs.

        The implementation of this point-in-polygon function is mostly correct, but may not be bulletproof. It ought to work for relatively small regions anywhere on the sky, but for instance it may get the sense wrong for regions that extend to cover both poles.

        Parameters:
        lon0 - test point latitude in degrees
        lat0 - test point longitude in degrees
        lonLats - 2N arguments (lon1, lat1, lon2, lat2, ..., lonN, latN) giving (longitude, latitude) vertices of an N-sided polygon in degrees
        Returns:
        true iff test point is inside, or on the border of, the polygon