The algorithm

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The algorithm uses simulated annealing. This is a general, randomized optimization technique that simulates a thermodynamic particle system. Each label is moved to a new random position within the limits given by its label descriptor. The quality of the new position is calculated and compared to the quality of the old position. If the quality has not improved, the label is moved back to the old position. The amount of movement is controlled by a conceptual temperature: when the system is hot, the labels can move long distances, producing potentially large global quality improvements. When the system cools down, the move distances become smaller and hence focus on local fine-tuning of the position.

Each label has its own label descriptor. The label descriptor describes the path on which the label can move. If a label must be placed at a city in a geographic map, then its label descriptor makes sure that the label is always placed close to the graphics that represent the city. If a label must be placed at a specific point, the IlvAnnealingPointLabelDescriptor can be used and describes an approximately elliptical path around the point. If a label must be placed at a polyline, the IlvAnnealingPolylineLabelDescriptor can be used and describes a boundary path at both sides of the polyline.

Annealing Label Layout algorithm Example

In CSS

The sample below shows how to use CSS syntax to declare labels at nodes of type IlvGeneralNode. The specification can be loaded as a style file into an application that uses the IlvDiagrammer class (see Graph layout in Rogue Wave JViews Diagrammer).

SDM {
    LabelLayout: "true";
}

LabelLayout {
    enabled: "true";
    labelOffset: “5”;
    obstacleOffset: “10”;
}

node {
    class: "ilog.views.sdm.graphic.IlvGeneralNode";
    label: "@name";
    labelPosition: "Left";
    labelSpacing: "2.0";
}

node:labelLayout {
    maxDistFromPath: "5";
}

In Java™

The following code sample uses the IlvAnnealingLabelLayout class. This code sample shows how to perform an Annealing Label Layout on a manager directly.:

 ...
import ilog.views.*;
import ilog.views.graphlayout.labellayout.*;
import ilog.views.graphlayout.labellayout.annealing.*;
 ...
IlvManager manager = new IlvManager();
IlvManagerView view = new IlvManagerView(manager);
 
 ... /* Fill in here code that fills the manager with labels and obstacles */
 
IlvAnnealingLabelLayout layout = new IlvAnnealingLabelLayout();
layout.attach(manager);

/* Assume: label1 should be placed at the right side of rectangular node1 */
layout.setLabelDescriptor(
          label1,
          new IlvAnnealingPointLabelDescriptor(
                label1, node1, IlvAnnealingPointLabelDescriptor.RECTANGULAR,
                IlvDirection.Right));
 
... /* Fill in here code that sets descriptors for all other labels */
 
IlvLabelLayoutReport layoutReport = layout.performLayout();
if (layoutReport.getCode() == IlvLabelLayoutReport.LAYOUT_DONE)
     System.out.println("Layout done.");
else
     System.out.println("Layout not done, code = " + 
                                   layoutReport.getCode());

Current section

Annealing label layout