The map loader

Loading a predefined map format

To load a predefined map format, use the load method. This method first tries to determine the file format according to the naming rules set forth in the specifications of the different formats, and initializes the appropriate reader. The method then loads the map into the manager associated with the map loader.

The following example shows how to import a .shp file (Shapefile format) into a JViews Maps manager using the map loader:

IlvMapLoader loader = new IlvMapLoader(manager);
try {
  loader.load("myShapeFile.shp");
} catch (IlvMapFormatException e) {
  // Occurs if there is a format error in the file.
  e.printStackTrace();
} catch (IOException e) {
  // Occurs if there is another IO error.
  e.printStackTrace();
}

A complete example of how to import a file using the map loader and save it in the .ilv format can be found in the following file:

<installdir> /jviews-maps810/codefragments/use_map_loader/src/UseMapLoader.java

Loading nongeoreferenced files

When you load a map into a JViews Maps manager using the map loader, this map is automatically displayed in the coordinate system associated with the manager provided that the format of the source data is georeferenced. The IlvMapFeatureIterator interface has an isGeoreferenced method that you can use to know whether a file is georeferenced. Most of the cartographic files are georeferenced. This is the case for files of the DTED format. Some other cartographic formats, such as Shapefile, are not georeferenced.

When loading data from a file that is not georeferenced, and in the absence of any other indications, the map loader is unable to reproject the source data within the target coordinate system (the one associated with the manager).

Note

If you load several source files of the Shapefile format whose projection is unknown in the same manager, objects are positioned correctly. However, if you try to import data of another format in the manager, the relative position of objects from different source formats are inaccurate.

If you read a file whose format is not georeferenced, but you know the coordinate system in which the data is expressed, you can provide this information to the IlvMapLoader using the setDefaultCoordinateSystem method.

The following example shows how to import a Shapefile whose projection is known to be geographic into a manager that is in a Mercator projected coordinate system:

// Initialize the manager for the mercator projection.
IlvProjection p = new IlvMercatorProjection();
IlvProjectedCoordinateSystem pcs = 
       new IlvProjectedCoordinateSystem("mercator", p);
IlvCoordinateSystemProperty csProperty = 
      new IlvCoordinateSystemProperty(pcs);
manager.setNamedProperty(csProperty);

// Create a map loader.
IlvMapLoader mapLoader = new IlvMapLoader(manager);

// Load other data.
....

// Load a Shapefile expressed in geographic coordinate system. mapLoader.setDefaultCoordinateSystem(IlvGeographicCoordinateSystem.WGS84);
mapLoader.load("myShapeFile.shp");

Specifying a renderer

If you want an IlvMapLoader object to use a specific renderer, specify it as the second argument of its load method, as shown below:

IlvFeatureRenderer renderer = new IlvDefaultCurveRenderer();
mapLoader.load(myIterator, renderer);
IlvMapLoader mapLoader = new IlvMapLoader(manager);

The file <installdir> /jviews-maps810/codefragments/renderer/src/Viewer.java shows how to use specific renderers with a map loader reading data that has the Shapefile format. For specific renderers, see the examples provided in Creating a colored line renderer and Extending an existing renderer.

Executing this file loads the following two files into the viewer:

The <installdir>/doc/usermansrc/maps/renderer/HYLINE.SHP file defines contour lines for the region of Manila (Philippines). The HYLNVAL attribute holds the elevation associated with each contour line. Colors are applied to contour lines using the default elevation color model supplied with JViews Maps. See IlvIntervalColorModel.MakeElevationColorModel .
The <installdir>/doc/usermansrc/maps/renderer/PPPOINT.SHP file defines points representing populated areas in the region of Manila (Philippines). The PPPTNAME attribute holds the name of the town, if it is known. In this case, this name appears next to the IlvMarker object that represents the town.

Attaching attributes to graphic objects

The map loader can automatically attach attributes to the graphic objects that it creates when it loads a map. For this, use the setAttachingAttributes method, as shown in the following example:

IlvMapLoader loader = new IlvMapLoader(manager);
loader.setAttachingAttributes(true);
try {
  loader.load("myShapeFile.shp");
} catch (IlvMapFormatException e) {
  // Occurs if there is a format error in the file.
  e.printStackTrace();
} catch (IOException e) {
  // Occurs if there is an other IO error.
  e.printStackTrace();
}

Extending the IlvMapLoader class

This section shows how to subtype the IlvMapLoader class so that it can recognize a file format other than the JViews Maps predefined formats.

The method makeFeatureIterator of this class creates the reader that recognizes the format of the file specified as its parameter. In the following example, the IlvMapLoader class is derived and the method overridden so that it can recognize the format of the polyline file presented in the section Developing a new reader and initialize the appropriate reader. It is assumed that the file has the .pol extension.

public class MyMapLoader extends IlvMapLoader
{
  /**
   * Constructor.
   */
  public MyMapLoader(IlvManager manager) {
    super(manager);
  }
  /**
   * Overrides the makeFeatureIterator method from super class.
   */
  public IlvMapFeatureIterator makeFeatureIterator(String fileName)
    throws IOException
   {
    // Does superclass know the format of provided file?
    IlvMapFeatureIterator result = super.makeFeatureIterator(fileName);
    // If not, try with the polygon reader.
    if (result == null) {
      // Test extension.
      int length = fileName.length();
      // .pol are polylines files.
      if (length > 4) {
        String suffix = fileName.substring(length - 4);
        if (suffix.toLowerCase().equals(".pol")) {
          try {
            return new OptimizedPolylineReader(fileName);
          } catch (IlvMapFormatException e) {
            return null;
          }
        }
      }
    }
    return result;
  }

The makeFeatureIterator method first attempts to get an IlvMapFeatureIterator from its superclass. If the file is not recognized, it tries to determine whether the file extension provided (in this example, .pol ) corresponds to that of the file to be read. If the result of the test is true , it creates the appropriate reader, which in this case is the optimized reader created in Optimizing the reader.

If the file does not contain a header, an IlvMapFormatException is thrown and the method returns the null pointer to indicate that it was not able to identify the file format.

The complete source code for this customized map loader can be found in the following file:

<installdir> /jviews-maps810/codefragments/readers/src/MyMapLoader.java