DivertedSingularityAiming.java
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* CS licenses this file to You under the Apache License, Version 2.0
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package org.orekit.models.earth.tessellation;
import java.util.Collections;
import java.util.List;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.geometry.spherical.twod.S2Point;
import org.hipparchus.geometry.spherical.twod.SphericalPolygonsSet;
import org.hipparchus.util.FastMath;
import org.orekit.bodies.GeodeticPoint;
/** Class used to orient tiles such that there are no singularities within the zone of interest.
* <p>
* This class is mainly useful for {@link EllipsoidTessellator#sample(org.hipparchus.geometry.spherical.twod.SphericalPolygonsSet,
* double, double) sampling} a zone on ground when the grid directions is not really important
* and when the zone contains the pole, which is a singular point for both
* {@link ConstantAzimuthAiming} and {@link AlongTrackAiming}.
* </p>
* @see AlongTrackAiming
* @see ConstantAzimuthAiming
* @author Luc Maisonobe
*/
public class DivertedSingularityAiming implements TileAiming {
/** Singularity location. */
private final Vector3D singularity;
/** Singularity location. */
private final GeodeticPoint singularityGP;
/** Dipole moment. */
private final Vector3D moment;
/** Simple constructor.
* @param forbiddenZone zone out of which singularity should be diverted
*/
public DivertedSingularityAiming(final SphericalPolygonsSet forbiddenZone) {
final S2Point outside = forbiddenZone.getEnclosingCap().getCenter().negate();
this.singularity = outside.getVector();
this.singularityGP = new GeodeticPoint(0.5 * FastMath.PI - outside.getPhi(), outside.getTheta(), 0.0);
this.moment = singularity.orthogonal();
}
/** {@inheritDoc} */
@Override
public List<GeodeticPoint> getSingularPoints() {
return Collections.singletonList(singularityGP);
}
/** {@inheritDoc} */
@Override
public Vector3D alongTileDirection(final Vector3D point, final GeodeticPoint gp) {
// compute the dipole field at point
final Vector3D p = new S2Point(gp.getLongitude(), 0.5 * FastMath.PI - gp.getLatitude()).getVector();
final Vector3D r = p.subtract(singularity).normalize();
final Vector3D field = new Vector3D(3.0 * Vector3D.dotProduct(moment, r), r, -1.0, moment);
// the aiming direction is the horizontal component of the field
final Vector3D horizontal = new Vector3D(1, field, -Vector3D.dotProduct(field, p), p);
return horizontal.normalize();
}
}