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World Wind is a collection of components that interactively display 3D geographic information within Java applications or applets.
/*
* Copyright (C) 2012 United States Government as represented by the Administrator of the
* National Aeronautics and Space Administration.
* All Rights Reserved.
*/
package gov.nasa.worldwind.util;
import gov.nasa.worldwind.geom.*;
import gov.nasa.worldwind.globes.Globe;
/**
* Contains methods to resolve ray intersections with the terrain.
* @author Patrick Murris
* @version $Id: RayCastingSupport.java 1171 2013-02-11 21:45:02Z dcollins $
*/
public class RayCastingSupport
{
private static double defaultSampleLength = 100; // meters
private static double defaultPrecision = 10; // meters
/**
* Compute the intersection Position of the globe terrain with the ray starting
* at origin in the given direction. Uses default sample length and result precision.
* @param globe the globe to intersect with.
* @param origin origin of the ray.
* @param direction direction of the ray.
* @return the Position found or null.
*/
public static Position intersectRayWithTerrain(Globe globe, Vec4 origin, Vec4 direction)
{
return intersectRayWithTerrain(globe, origin, direction, defaultSampleLength, defaultPrecision);
}
/**
* Compute the intersection Position of the globe terrain with the ray starting
* at origin in the given direction. Uses the given sample length and result precision.
* @param globe the globe to intersect with.
* @param origin origin of the ray.
* @param direction direction of the ray.
* @param sampleLength the sampling step length in meters.
* @param precision the maximum sampling error in meters.
* @return the Position found or null.
*/
public static Position intersectRayWithTerrain(Globe globe, Vec4 origin, Vec4 direction,
double sampleLength, double precision)
{
if (globe == null)
{
String msg = Logging.getMessage("nullValue.GlobeIsNull");
Logging.logger().severe(msg);
throw new IllegalArgumentException(msg);
}
if (origin == null || direction == null)
{
String msg = Logging.getMessage("nullValue.Vec4IsNull");
Logging.logger().severe(msg);
throw new IllegalArgumentException(msg);
}
if (sampleLength < 0)
{
String msg = Logging.getMessage("generic.ArgumentOutOfRange", sampleLength);
Logging.logger().severe(msg);
throw new IllegalArgumentException(msg);
}
if (precision < 0)
{
String msg = Logging.getMessage("generic.ArgumentOutOfRange", precision);
Logging.logger().severe(msg);
throw new IllegalArgumentException(msg);
}
Position pos = null;
direction = direction.normalize3();
// Check whether we intersect the globe at it's highest elevation
Intersection inters[] = globe.intersect(new Line(origin, direction), globe.getMaxElevation());
if (inters != null)
{
// Sort out intersection points and direction
Vec4 p1 = inters[0].getIntersectionPoint();
Vec4 p2 = null;
if (p1.subtract3(origin).dot3(direction) < 0)
p1 = null; // wrong direction
if (inters.length == 2)
{
p2 = inters[1].getIntersectionPoint();
if (p2.subtract3(origin).dot3(direction) < 0)
p2 = null; // wrong direction
}
if (p1 == null && p2 == null) // both points in wrong direction
return null;
if (p1 != null && p2 != null)
{
// Outside sphere move to closest point
if (origin.distanceTo3(p1) > origin.distanceTo3(p2))
{
// switch p1 and p2
Vec4 temp = p2;
p2 = p1;
p1 = temp;
}
}
else
{
// single point in right direction: inside sphere
p2 = p2 == null ? p1 : p2;
p1 = origin;
}
// Sample between p1 and p2
Vec4 point = intersectSegmentWithTerrain(globe, p1, p2, sampleLength, precision);
if (point != null)
pos = globe.computePositionFromPoint(point);
}
return pos;
}
/**
* Compute the intersection Vec4 point of the globe terrain with a line segment
* defined between two points. Uses the default sample length and result precision.
* @param globe the globe to intersect with.
* @param p1 segment start point.
* @param p2 segment end point.
* @return the Vec4 point found or null.
*/
public static Vec4 intersectSegmentWithTerrain(Globe globe, Vec4 p1, Vec4 p2)
{
return intersectSegmentWithTerrain(globe, p1, p2, defaultSampleLength, defaultPrecision);
}
/**
* Compute the intersection Vec4 point of the globe terrain with the a segment
* defined between two points. Uses the given sample length and result precision.
* @param globe the globe to intersect with.
* @param p1 segment start point.
* @param p2 segment end point.
* @param sampleLength the sampling step length in meters.
* @param precision the maximum sampling error in meters.
* @return the Vec4 point found or null.
*/
public static Vec4 intersectSegmentWithTerrain(Globe globe, Vec4 p1, Vec4 p2,
double sampleLength, double precision)
{
if (globe == null)
{
String msg = Logging.getMessage("nullValue.GlobeIsNull");
Logging.logger().severe(msg);
throw new IllegalArgumentException(msg);
}
if (p1 == null || p2 == null)
{
String msg = Logging.getMessage("nullValue.Vec4IsNull");
Logging.logger().severe(msg);
throw new IllegalArgumentException(msg);
}
if (sampleLength < 0)
{
String msg = Logging.getMessage("generic.ArgumentOutOfRange", sampleLength);
Logging.logger().severe(msg);
throw new IllegalArgumentException(msg);
}
if (precision < 0)
{
String msg = Logging.getMessage("generic.ArgumentOutOfRange", precision);
Logging.logger().severe(msg);
throw new IllegalArgumentException(msg);
}
Vec4 point = null;
// Sample between p1 and p2
Line ray = new Line(p1, p2.subtract3(p1).normalize3());
double rayLength = p1.distanceTo3(p2);
double sampledDistance = 0;
Vec4 sample = p1;
Vec4 lastSample = null;
while (sampledDistance <= rayLength)
{
Position samplePos = globe.computePositionFromPoint(sample);
if (samplePos.getElevation() <= globe.getElevation(samplePos.getLatitude(), samplePos.getLongitude()))
{
// Below ground, intersection found
point = sample;
break;
}
if (sampledDistance >= rayLength)
break; // break after last sample
// Keep sampling
lastSample = sample;
sampledDistance = Math.min(sampledDistance + sampleLength, rayLength);
sample = ray.getPointAt(sampledDistance);
}
// Recurse for more precision if needed
if (point != null && sampleLength > precision && lastSample != null)
point = intersectSegmentWithTerrain(globe, lastSample, point, sampleLength / 10, precision);
return point;
}
}