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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.symbology;
import gov.nasa.worldwind.geom.*;
import gov.nasa.worldwind.globes.Globe;
import gov.nasa.worldwind.render.DrawContext;
import gov.nasa.worldwind.util.Logging;
import java.util.*;
/**
* Utility methods for working with tactical graphics.
*
* @author pabercrombie
* @version $Id: TacticalGraphicUtil.java 1171 2013-02-11 21:45:02Z dcollins $
*/
public class TacticalGraphicUtil
{
/**
* Convert a list of cartesian points to Positions.
*
* @param globe Globe used to convert points to positions.
* @param points Points to convert.
*
* @return List of positions computed from cartesian points.
*/
public static List asPositionList(Globe globe, Vec4... points)
{
List positions = new ArrayList(points.length);
for (Vec4 point : points)
{
positions.add(globe.computePositionFromPoint(point));
}
return positions;
}
/**
* Get the date range from a graphic's modifiers. This method looks at the value of the AVKey.DATE_TIME
* modifier, and returns the results as a two element array. If the value of the modifier is an
* Iterable, then this method returns the first two values of the iteration. If the value of the
* modifier is a single object, this method returns an array containing that object and null.
*
* @param graphic Graphic from which to retrieve dates.
*
* @return A two element array containing the altitude modifiers. One or both elements may be null.
*/
public static Object[] getDateRange(TacticalGraphic graphic)
{
Object date1 = null;
Object date2 = null;
Object o = graphic.getModifier(SymbologyConstants.DATE_TIME_GROUP);
if (o instanceof Iterable)
{
Iterator iterator = ((Iterable) o).iterator();
if (iterator.hasNext())
{
date1 = iterator.next();
}
if (iterator.hasNext())
{
date2 = iterator.next();
}
}
else
{
date1 = o;
}
return new Object[] {date1, date2};
}
/**
* Get the altitude range from the graphic's modifiers. This method looks at the value of the
* AVKey.ALTITUDE modifier, and returns the results as a two element array. If the value of the
* modifier is an Iterable, then this method returns the first two values of the iteration. If the
* value of the modifier is a single object, this method returns an array containing that object and
* null.
*
* @param graphic Graphic from which to retrieve dates.
*
* @return A two element array containing the altitude modifiers. One or both elements may be null.
*/
public static Object[] getAltitudeRange(TacticalGraphic graphic)
{
Object alt1 = null;
Object alt2 = null;
Object o = graphic.getModifier(SymbologyConstants.ALTITUDE_DEPTH);
if (o instanceof Iterable)
{
Iterator iterator = ((Iterable) o).iterator();
if (iterator.hasNext())
{
alt1 = iterator.next();
}
if (iterator.hasNext())
{
alt2 = iterator.next();
}
}
else
{
alt1 = o;
}
return new Object[] {alt1, alt2};
}
/**
* Position one or two labels some distance along the path. Top and bottom labels are often positioned above and
* below the same point, so this method supports positioning a pair of labels at the same point. The label offsets
* determine how the labels draw in relation to the line.
*
* @param dc Current draw context.
* @param positions Positions that describe the path.
* @param label1 First label to position.
* @param label2 Second label to position. (May be null.)
* @param distance Distance along the path at which to position the labels.
*/
public static void placeLabelsOnPath(DrawContext dc, Iterable positions,
TacticalGraphicLabel label1,
TacticalGraphicLabel label2, double distance)
{
Iterator iterator = positions.iterator();
Globe globe = dc.getGlobe();
Position pos1 = null;
Position pos2;
Vec4 pt1, pt2;
double length = 0;
double thisDistance = 0;
pos2 = iterator.next();
pt2 = globe.computePointFromLocation(pos2);
while (iterator.hasNext() && length < distance)
{
pos1 = pos2;
pt1 = pt2;
pos2 = iterator.next();
pt2 = globe.computePointFromLocation(pos2);
thisDistance = pt2.distanceTo2(pt1);
length += thisDistance;
}
if (pos1 != null && pos2 != null && thisDistance > 0)
{
double delta = length - distance;
LatLon ll = LatLon.interpolateGreatCircle(delta / thisDistance, pos1, pos2);
pos1 = new Position(ll, 0);
label1.setPosition(pos1);
label1.setOrientationPosition(pos2);
if (label2 != null)
{
label2.setPosition(pos1);
label2.setOrientationPosition(pos2);
}
}
}
/**
* Compute a point along a Bezier curve defined by a list of control points. The first and last points should mark
* the start and end of the curve.
*
* This function implements the Bezier curve equation from "Mathematics for 3D Game Programming and Computer
* Graphics, Second Edition" by Eric Lengyel (equation 15.16, pg. 458).
*
* A typical usage looks like this:
*
* Vec4[] controlPoints = ... // Determine control points appropriate for your curve
*
* List curvePositions = new ArrayList();
* int[] coefficients = new int[controlPoints.length];
*
* int intervals = 32;
* double delta = 1.0 / intervals;
* for (int i = 0; i < intervals; i++)
* {
* double t = i * delta;
* Vec4 pt = TacticalGraphicUtil.bezierCurve(controlPoints, t, coefficients);
* Position pos = globe.computePositionFromPoint(p);
* curvePositions.add(pos);
* }
*
*
* @param controlPoints Control points for the curve.
* @param t Interpolation parameter in the range [0..1].
* @param coefficients Array to store binomial coefficients between invocations of this function. On the first
* invocation, pass an int[] with length equal to the controlPoints array. bezierCurve will
* populate the array on the first invocation, and reuse the computed values on subsequent
* invocations.
*
* @return A point along the curve.
*/
public static Vec4 bezierCurve(Vec4[] controlPoints, double t, int[] coefficients)
{
if (coefficients == null || controlPoints == null)
{
String message = Logging.getMessage("nullValue.ArrayIsNull");
Logging.logger().severe(message);
throw new IllegalArgumentException(message);
}
if (coefficients.length != controlPoints.length)
{
String message = Logging.getMessage("generic.ArrayInvalidLength", coefficients.length);
Logging.logger().severe(message);
throw new IllegalArgumentException(message);
}
if (coefficients[0] != 1)
{
binomial(coefficients.length - 1, coefficients);
}
int n = controlPoints.length - 1;
Vec4 r = Vec4.ZERO;
for (int k = 0; k <= n; k++)
{
double c = coefficients[k] * Math.pow(t, k) * Math.pow(1 - t, n - k);
r = r.add3(controlPoints[k].multiply3(c));
}
return r;
}
/**
* Compute binomial coefficients for a polynomial of order n. Stated another way, computes the nth row of Pascal's
* triangle.
*
* @param n Order of polynomial for which to calculate coefficients.
* @param coefficients Array to receive coefficients. The length of this array must be n + 1.
*/
protected static void binomial(int n, int[] coefficients)
{
if (coefficients == null)
{
String message = Logging.getMessage("nullValue.ArrayIsNull");
Logging.logger().severe(message);
throw new IllegalArgumentException(message);
}
if (coefficients.length != n + 1)
{
String message = Logging.getMessage("generic.ArrayInvalidLength", coefficients.length);
Logging.logger().severe(message);
throw new IllegalArgumentException(message);
}
// Algorithm from "Data Structures and Algorithms with Object-Oriented Design Patterns in Java" by Bruno R.
// Preiss (http://www.brpreiss.com/books/opus5/html/page460.html)
for (int i = 0; i <= n; i++)
{
coefficients[i] = 1;
for (int j = i - 1; j > 0; j--)
{
coefficients[j] += coefficients[j - 1];
}
}
}
}