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XS.c  view on Meta::CPAN

 *
 *      To go the other way, as this program does, undo the final translation,
 *      rotation, and scaling.  The z-value Pz of the point on the x-y-z sphere
 *      satisfies the quadratic Azz+Bz+c=0, where
 *              A = (ExWz-EzWx)^2 + (EyWzx-EzWy)^2 + (ExWy-EyWx)^2;
 *              B = -2[(Ex cos(arc to W) - Wx cos(arc to E))(ExWz-EzWx) -
 *                      (Ey cos(arc to W) -Wy cos(arc to E))(EyWz-EzWy)];
 *              C = (Ex cos(arc to W) - Wx cos(arc to E))^2 +
 *                      (Ey cos(arc to W) - Wy cos(arc to E))^2 -
 *                      (ExWy - EyWx)^2.
 *      Solve with the quadratic formula.  The latitude is simply the
 *      arc sine of Pz.  Px and Py satisfy
 *              ExPx + EyPy + EzPz = cos(arc to E);
 *              WxPx + WyPy + WzPz = cos(arc to W).
 *      Substitute Pz's value, and solve linearly to get Px and Py.
 *      The longitude is the arc tangent of Px/Py.
 *      Finally, this latitude and longitude are spherical; use the
 *      inverse polynomial approximation on the latitude to get the
 *      ellipsoidal earth latitude, and add 52 degrees to the longitude.
 */

XS.xs  view on Meta::CPAN

 *
 *      To go the other way, as this program does, undo the final translation,
 *      rotation, and scaling.  The z-value Pz of the point on the x-y-z sphere
 *      satisfies the quadratic Azz+Bz+c=0, where
 *              A = (ExWz-EzWx)^2 + (EyWzx-EzWy)^2 + (ExWy-EyWx)^2;
 *              B = -2[(Ex cos(arc to W) - Wx cos(arc to E))(ExWz-EzWx) -
 *                      (Ey cos(arc to W) -Wy cos(arc to E))(EyWz-EzWy)];
 *              C = (Ex cos(arc to W) - Wx cos(arc to E))^2 +
 *                      (Ey cos(arc to W) - Wy cos(arc to E))^2 -
 *                      (ExWy - EyWx)^2.
 *      Solve with the quadratic formula.  The latitude is simply the
 *      arc sine of Pz.  Px and Py satisfy
 *              ExPx + EyPy + EzPz = cos(arc to E);
 *              WxPx + WyPy + WzPz = cos(arc to W).
 *      Substitute Pz's value, and solve linearly to get Px and Py.
 *      The longitude is the arc tangent of Px/Py.
 *      Finally, this latitude and longitude are spherical; use the
 *      inverse polynomial approximation on the latitude to get the
 *      ellipsoidal earth latitude, and add 52 degrees to the longitude.
 */