ilog.views.graphlayout.labellayout.annealing

Class IlvAnnealingLabelDescriptor

java.lang.Object

ilog.views.graphlayout.labellayout.annealing.IlvAnnealingLabelDescriptor

Direct Known Subclasses:

IlvAnnealingPointLabelDescriptor, IlvAnnealingPolylineLabelDescriptor

public abstract class IlvAnnealingLabelDescriptor
extends java.lang.Object

The class IlvAnnealingLabelDescriptor is the abstract base class of all label descriptors. A label descriptor is used to describe how a label can move during the Simulated Annealing label layout. One subclass is for instance the IlvAnnealingPointLabelDescriptor that is used to describe that a label must be placed close to a fixed point, as for instance needed to label the cities of a map. Another subclass is the IlvAnnealingPolylineLabelDescriptor that is used to describe that a label must be placed near a polyline link of a graph.

Simulated Annealing moves the label basically on a path. It allows the label to leave the path in a very close area, so the actual position can be described by a point on the path plus the distance of the label from this path. For instance, for the IlvAnnealingPointLabelDescriptor, the path may be approximately a circle (in fact, it is an elliptically rounded rectangle), that is, the label can move along this path around the reference point of the label. To simplify the implementation of different paths, the Simulated Annealing does not use Cartesian coordinates, it only specifies the abstract path location (the distance you have to go along the path from the start point of the path to the current path point), and the distance from this path point. The translation of this abstract location into the effective Cartesian coordinates of the label is done by the implementation of the method #setPosition(double, double). This allows you to use the algorithm with different paths, by subclassing the IlvAnnealingLabelDescriptor and implementing your version of #setPosition(double, double).

For instance, assume that the label should move on a circle between radius 10 and 15 around the origin. The following code implements a corresponding label descriptor:

  public class MyCircleLabelDescriptor
    extends IlvAnnealingLabelDescriptor
  {
    public MyCircleLabelDescriptor(Object label)
    {
      super(label); 
    }
    public void initialize(IlvLabelingModel labelingModel)
    {
      // set the maximum location:
      // circumference of circle with radius 10
      maxPathLocation = 2 * Math.PI * 10;
      // path is at radius 10, hence max distance from path is (15 - 10) = 5
      maxDistFromPath = 5;
    } 
    public void setPosition(double pathLocation, double distFromPath)
    {
      // path radius is 10. Radius for position is 10 + distFromPath,
      // because distFromPath is between 0 and 5
      updatePosition(
            (double)((10 + distFromPath) * Math.cos(pathLocation / 10));
            (double)((10 + distFromPath) * Math.sin(pathLocation / 10)) );
      actPathLocation = pathLocation;
      actDistFromPath = distFromPath;
    }
    // assume that the preferred position is the path location 0 and distance
    // 0 from the path.
    public void setTowardsPreferredPosition(
      double pathLocation, double distFromPath, int i, int maxI)
    {
      if (pathLocation <= maxPathLocation/2) {
        // clockwise towards the preferred position
        setPosition(pathLocation - pathLocation * (i+1) / maxI,
                    distFromPath - distFromPath * (i+1) / maxI);
      }
      else {
        // counter-clockwise towards the preferred position
        setPosition(pathLocation + pathLocation * (i+1) / maxI,
                    distFromPath + distFromPath * (i+1) / maxI);
      } 
    }
  }
  

CSS example:

This class cannot be instantiated because it is an abstract class.

Method Summary

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait