Introduction to Layers and Styles

Programming with JViews Maps > Introducing the Main Classes > Map Layers and Map Styles > Introduction to Layers and Styles

Introduction to Layers and Styles

INDEX

PREVIOUS NEXT

The class relationship for layers and styles is shown in Figure 1.11.

Figure 1.11 Layer and Style UML Diagram

In this section you will find information on the following topics:

The source code for the Map Builder demonstration, which contains all of the code described in this section, can be found at <installdir>/jviews-maps81/samples/mapbuilder/index.html

About Map Layers

The IlvMapLayer class represents a map layer, that is, a cartographic theme. It associates a style (IlvMapStyle or one of its subclasses) with an IlvManagerLayer containing graphic objects.

Map Layers are arranged in a tree structure, and stored in the manager using the IlvMapLayerTreeProperty, see Map Layer Tree.

Each map layer is attached to an IlvMapLayerTreeNode, which contains the necessary information on parent and child layers. You can use this node to step through layer hierarchy as follows:

IlvMapLayerTreeNode node = mapLayer.getNode();
for (int i = 0; i < node.getChildCount(); i++) {
  IlvMapLayerTreeNode child=(IlvMapLayerTreeNode) node.getChildAt(i);
  IlvMapLayer childLayer = (IlvMapLayer) node.getUserObject(); 
  ... do something with child layer
}

Most map layers are attached to a data source, which is responsible for populating the manager layer with the correct graphic objects when the map data is loaded (possibly on-demand-loading) and reprojection times. The exception to this rule is the composite layer. Composite layers are only used to group a set of sub-layers and manage their styles using attribute inheritance (See below).

Using Map Styles

Every style in JViews Maps is a subclass of the base IlvMapStyle class.

This class provides access to a set of attributes, usually also accessible by a setter/getter pair, depending on each style subclass.

For example, you can change the view visibility setting using:

style.setAttribute(IlvMapStyle.VISIBLE_IN_VIEW,Boolean.TRUE);

or,

style.setVisibleInView(true);

You can catch any change in the map style by writing and registering a listener on it. For example:

StyleListener listener = new StyleListener() {
   public void styleChanged(StyleEvent event) {
      if(IlvMapStyle.ALPHA.equals(event.getAttribute())) {
         //  ... do something when transparency changes
      }
   }
};
...
myStyle.addStyleListener(listener);

Style Hierarchy

Styles form a hierarchy and attribute values can be inherited through this hierarchy. If a style attribute is inherited from a parent style, that parent attribute value is used when displaying objects using that style.

Although not enforced in the API, it is recommended that you make the style hierarchy the same as the map layer hierarchy. This can be done when the map layer is inserted in the layer tree model:

IlvMapLayerTreeModel ltm = IlvMapLayerTreeProperty.GetMapLayerTreeModel(manager);
ltm.addChild(parentLayer, layer);
IlvMapStyle parentStyle = layer.getParent().getStyle();
IlvMapStyle childStyle = layer.getStyle();
childStyle.setParent(parentStyle);

Common Styling Properties

Whatever the type of layer, its style always has the following base properties:

Table 1.2 Common Styling Properties

Property name	Contents
VISIBLE_IN_VIEW	Indicates whether the `IlvManagerLayer` is displayed on the map view.
VISIBLE_IN_OVERVIEW	Indicates whether the `IlvManagerLayer` is displayed on the map overview.
ATTRIBUTE_INFO	Contains the `IlvAttributeInfoProperty` used to describe all object properties. This is used to provide the list of possible property names displayed in the label attribute check box. This attribute cannot be changed by the user in the map layer tree panel.
LABEL_ATTRIBUTE	Contains either a null value, or the name of the property used when labeling this map layer (chosen usually in the list provided by the ATTRIBUTE_INFO attribute).
ALWAYS_ON_TOP	Indicates whether the attached map layer is placed on a normal or superimposing plane. This should be used only for overlay layers such as grids, labels, measures, and so on.
LEGEND_GROUP	A logical name, used and displayed to group map layers in the legend.
CATEGORY	An identifying name to group more than one layer on the same legend line.
ALPHA	The level of transparency of the manager layer.

PREVIOUS NEXT