java - 如何正确绘制路径？

Question

我目前正在重写路径绘制算法。我正在使用 apache-commons-math 的样条插值器来获得通过 2D 空间中所有给定点的平滑路径...

目前我有:

/**
 * Draws a route on a map.
 */
public class MapRouteDrawer {

  private static final SplineInterpolator splineInterpolator = new SplineInterpolator();

  /**
   * Draws the route to the screen, does nothing if null.
   */
  public static void drawRoute(final Graphics2D graphics, final RouteDescription routeDescription, final MapPanel view, final MapData mapData, final String movementLeftForCurrentUnits) {
    if (routeDescription == null) {
      return;
    }
    final Route route = routeDescription.getRoute();
    if (route == null) {
      return;
    }

    final Point[] points = getRoutePoints(routeDescription, mapData);
    final int xOffset = view.getXOffset();
    final int yOffset = view.getYOffset();
    final int jointsize = 10;
    final int numTerritories = route.getAllTerritories().size();
    //set thickness and color of the future drawings
    graphics.setStroke(new BasicStroke(3.5f, BasicStroke.CAP_ROUND, BasicStroke.JOIN_ROUND));
    graphics.setPaint(Color.red);
    graphics.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

    if(Arrays.asList(points).contains(null)){//If the Array is null at some point
      return;
    }

    if(numTerritories <= 1 || points.length <= 2){
      drawLineWithTranslate(graphics, new Line2D.Float(routeDescription.getStart(), routeDescription.getEnd()), xOffset, yOffset);
      graphics.fillOval((routeDescription.getEnd().x - xOffset) - jointsize / 2, (routeDescription.getEnd().y - yOffset) - jointsize / 2, jointsize, jointsize);
    }
    else{
      drawCurvedPath(graphics, points, view);
    }
  }

  }

  private static double[] getIndex(Point[] points) {
    final double[] index = new double[points.length];
    for(int i = 0; i < points.length; i++){
      index[i] = i;
    }
    return index;
  }

  private static void drawLineWithTranslate(Graphics2D graphics, Line2D line2D, double translateX, double translateY) {
      final Line2D line = (Line2D) line2D;
      final Point2D point1 = new Point2D.Double(line.getP1().getX() - translateX, line.getP1().getY() - translateY);
      final Point2D point2 = new Point2D.Double(line.getP2().getX() - translateX, line.getP2().getY() - translateY);
      graphics.draw(new Line2D.Double(point1, point2));
  }

  private static Point[] getRoutePoints(RouteDescription routeDescription, MapData mapData){
    final List<Territory> territories = routeDescription.getRoute().getAllTerritories();
    final int numTerritories = territories.size();
    final Point[] points = new Point[numTerritories];
    for (int i = 0; i < numTerritories; i++) {
      points[i] = mapData.getCenter(territories.get(i));
    }
    if (routeDescription.getStart() != null) {
      points[0] = routeDescription.getStart();
    }
    if (routeDescription.getEnd() != null && numTerritories > 1) {
      points[numTerritories - 1] = new Point(routeDescription.getEnd());
    }
    return points;
  }

  private static double[] pointsXToDoubleArray(Point[] points){
    double[] result = new double[points.length];
    for(int i = 0; i < points.length; i++){
      result[i] = points[i].getX();
    }
    return result;
  }
  private static double[] pointsYToDoubleArray(Point[] points){
    double[] result = new double[points.length];
    for(int i = 0; i < points.length; i++){
      result[i] = points[i].getY();
    }
    return result;
  }

  private static double[] getCoords(PolynomialSplineFunction curve, float stepSize){
    final double[] coords = new double[(int) (curve.getN() / stepSize)];
    for(int i = 0; i < curve.getN() / stepSize; i++){
      coords[i] = curve.value(i * stepSize);
    }
    return coords;
  }

  private static void drawCurvedPath(Graphics2D graphics, Point[] points, MapPanel view){
    final double[] index = getIndex(points);
    final float stepSize = 0.01f;//TODO calculating a step size that makes sense
    final PolynomialSplineFunction xcurve = splineInterpolator.interpolate(index, pointsXToDoubleArray(points));
    final PolynomialSplineFunction ycurve = splineInterpolator.interpolate(index, pointsYToDoubleArray(points));
    final double[] xcoords = getCoords(xcurve, stepSize);
    final double[] ycoords = getCoords(ycurve, stepSize);

    for(int i = 1; i < xcoords.length; i++){
      //TODO maybe a line is not the best way to draw this...
      drawLineWithTranslate(graphics, new Line2D.Double(xcoords[i-1], ycoords[i-1], xcoords[i], ycoords[i]), view.getXOffset(), view.getYOffset());
    }
  }
}

这背后的想法是，由于 SplineInterpolator 只接受函数(例如 f(x) = y)并且 x 必须递增，因此我们将点数组分成 2 个 double 组并插值两次...< br/>首先是 X 值，然后是 Y 值...
作为 X 值，采用称为“索引”的“虚拟数组”，第一个值为 0，第二个值为 1，第三个值为 2，依此类推...
为了绘制这条路径，我从点 0 到 1、1 到 2、2 到 3 等等绘制一条线...

有两件事需要考虑......

1. 在索引中选择 1 作为步长有意义吗？这可能会导致不准确，因为 java double 只有 64 位，而我们使用静态 1 步长来拉伸(stretch)和压缩值。如果是这样，我可以改变什么来优化这个......
2. 第二，如何更好地绘制这两个 double 组？我尝试绘制多条线看起来不太好 - 这是因为我正在以太大的步长读取插值吗？

非常感谢任何帮助

编辑:

Answer 1

选择 1 作为“索引”数组的步长就是所谓的均匀参数化，除非您的数据点也分布相对均匀，否则通常不会产生良好的结果。我建议使用弦长参数化或向心参数化，如下所示:

t0 = 0.0
t1 = d1/L
t2 = t1 + d2/L  
t3 = t2 + d3/L
............
t(n-1)= 1.0.

哪里

d1=|P1-P0|^e, d2=|P2-P1|^e, d3=|P3-P2|^e and L = d1+d2+d3+.....d(n-1). 

对于弦长参数化，在上式中使用 e=1.0。对于向心参数化，使用 e=0.5。请注意，使用 e=0.0 只会导致统一参数化。如果您的数据点分布非常不均匀(即，点之间的距离有些很大，有些很小)，向心参数化通常会比弦长参数化产生更好的结果。