Describes map layers and map styles.

The class diagram for layers and styles is shown in Layer and Style UML Diagram.

The source code for the Map Builder demonstration, which contains all of the code described in this section, can be found at <installdir> /jviews-maps/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:

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).

About 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 on of:

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

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:

Common styling properties

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

The class diagram for map layers for graphic objects is shown in Layers for Graphic Objects UML Diagram.

Most map layers are used to manage graphic objects created from map features imported from various map data files. The styling options differ according to the content of each file and the map features imported by the different readers. For example, you do not style a polygon the same way you do an altitude raster image.

The IlvGeneralPathStyle class

The IlvGeneralPathStyle class is used for IlvMapGeneralPath stylable graphic objects. Generally, most vectorial map renderers provide a setUsingGeneralPath method to allow a choice between using general paths, which give a better aspect and capabilities, or regular polygons, which provide better performance.

The IlvPolylineStyle class

The IlvPolylineStyle class is used for IlvMapPolyline stylable objects (polygons or polylines without fill).

The IlvGraphicPathStyle class

The IlvGraphicPathStyle class is a subclass of IlvPolylineStyle and so provides all the attributes in The IlvPolylineStyle class. It provides the style for IlvMapGraphicPath objects (filled polygon areas), by adding:

The IlvPointStyle class

The IlvPointStyle class controls the style of map point ( IlvMapPoint) objects. It provides the following attributes:

The IlvMapTextStyle class

The IlvMapTextStyle class controls the style of map stylable label objects ( IlvMapText). It provides the following attributes:

The IlvRasterStyle class

The IlvRasterStyle class is used with IlvRasterIcon graphic objects, and provides attributes to control the appearance of the image:

The IlvMapCompositeStyle class

The IlvMapCompositeStyle class does not define any additional attributes. Its attribute list grows with its child list.

When adding a child style in a composite style, all the attributes of that child are added (if they did not exist) into the parent style. Those values can then be inherited for each child style – allowing the attributes for all children to be changed in one single place.

You can change the inheritance setting of each attribute by calling the setInherited method.

Label layers are created automatically on demand by the IlvMapLabeler property installed on the manager when the LABEL_ATTRIBUTE style attribute is changed on a registered layer.

The IlvMapLabelStyle class

The IlvMapLabelStyle class is used by the IlvMapAreaLabel, IlvMapLineLabel and IlvMapPointLabel classes, and controls the labeling parameters:

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

The IlvAbstractBaseGrid class

The IlvAbstractBaseGrid base class has subclasses IlvMGRSGrid and IlvLatLonGrid. It is a manager layer that, instead of drawing graphic objects ( IlvGraphic instances) added to it, displays a grid adapted to the current zoom level of the map.

This base grid also implements the IlvManagerViewDecoration interface, which allows you to display the grid on the screen, but prevents it from being displayed on printed material.

The IlvMGRSGrid class

The IlvMGRSGrid class displays a set of auto-adaptive MGRS standard grids and labels on top of a geographic view. This grid displays a list of Grid zones (either UPS or UTM zones), and their sub grids (100000m, 10000m, 1000m). Each grid or sub-grid is labeled using the standardized MGRS name for the current area.

You can create and add an MGRS grid on any geo-referenced manager view (that is, any view that supports the IlvCoordinateSystemProperty). For example, to add an MGRS grid containing all MGRS zones as a decoration of the view:

The IlvLatLonGrid class

The IlvLatLonGrid class displays a set of auto-adaptive grids and labels along latitude or longitude lines on top of a geographic view. If the grid is auto-adaptive, the step between each successive lat/lon line is dependant on the scale of the current view.

You can create and add an MGRS grid on any geo-referenced manager view (that is, any view that supports the IlvCoordinateSystemProperty). For example, to create a lat/lon grid layer:

By default, the IlvLatLonGrid creates only the points at the corners of each grid square. If you are using a coordinate system that transforms the map in a non-linear way (such as Orthographic projection, UTM projection, and so on), you can increase the number of intermediate points on each grid square in order to show a smoother version of the grid:

Writing specific grids

The easiest way to implement your own grid system is to start with an empty MGRS grid and then add your own zones to it. For examples of this, see the Map Builder GridManager class.

Integrating grids into map layers

As the grids are implemented as manager layers, you only need to connect these to an IlvMapLayer.

This map layer must be created, styled and integrated in the map layer tree model:

Then you can integrate the grid manager layer into it:

You can also use an IlvDelayedDecoration manager layer to encapsulate the grid. Whenever the user moves or zooms the grid rapidly, a simplified version of the grid is used, which displays more quickly. When the user stops moving or zooming the grid, the full grid is displayed:

The IlvGridStyle class

The IlvGridStyle class is used when displaying grids. It defines the following attributes:

As a result of the use of the IlvMapStyleControllerProperty property of the manager (and its underlying IlvMapStyleController), layer styles are dependant on the current scale of the map. Every style attribute of a map layer can be different at different scales.

One of the most widely used attribute changes is the VISIBLE_IN_VIEW attribute, which is used to show and hide different map layers at particular scales. Using the same mechanism, your users can also change colors, line thickness, decorations and so on. Whenever the scale changes, the scale controller can change the current map layer styles, if required. This change of style usually triggers a view repaint, because the attributes of the objects have changed.

Some objects also listen to these style changes in order to re-render themselves. For example, if the color model of a raster style changes, all the images that depend on the style need to be re-created.

You can add dynamic styles with API calls such as:

When you add dynamic styles, be careful to ensure that you still manage style inheritance. When adding a new map layer into a parent layer, you can do this as follows:

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

A IlvMapAttributeFilter object is used to compute the value of a styling attribute from a value found in an IlvGraphic instance. Typically, this value is retrieved from the IlvFeatureAttributeProperty named property attached to a IlvGraphic object. To install such a filter, you set it to an IlvMapStyle object.

The following example shows a custom filter class that defines the foreground of map graphic objects according to their “VALUE” feature attribute.

The following code example shows how to install a custom filter class in a map layer style.

Once the filter is installed, each request to retrieve an attribute value is passed to the get method of the filter.