Advanced Example3

Java API for KML - Advanced Example3

[ The concept ] [ Mobile Phone Subscriptions 2008. ] [ The Code ]

The concept

This series of more sophisticated JAK examples is trying to show the capabilities what is possible with KML in Java. They show the usage of JAK for generating some nice-looking KML files, which can be viewed with Google Earth.

Important!
JAK only works if all dependencies are resolved! That are mainly JAK and JAXB! For further instructions check out the FAQ.

Mobile Phone Subscriptions 2008.

The third example integrates statistic data to the polygons. It reads data of mobile phone subscriptions in 2008 from a CSV and set the height of the polygons to the value of the data for each country. The data can be found on this site: data.un.org and is saved as CSV file. The 3D Polygons for the border of each country are created the same way as described in Advanced Example2.

Figure 1: Mobile Phone Subscriptions 2008 in Google Earth.

The Code

In this example the CSV date file is parsed and the values are stored in a HashMap<String, Double> The country name is the key, while the value is the mobile phone subscriptions value. The program traverse through the countries of the world (saved as placemark objects) and obtained from the World Borders Dataset and checks if mobile subscription data exist for the current country. The height and the color of the country are now set according to the mobile subscription value.

Listing 1: Mobile Phone Subscriptions 2008 in Google Earth

HashMap<String, Double> data = Utils.readCSVDoubleData("src/main/resources/exampledata/mobile_phone_2008.csv", 0, 3);
double max = data.get("maximum");
int minPolyHeight = 308000;
int maxPolyHeight = 2692000; // real max = 3000000 - 308000 = 2692000

Kml unmarshal = Kml.unmarshal(new File("src/main/resources/exampledata/worldBorders.kml"));
Document document = (Document) unmarshal.getFeature();
document.setName("JAK Example3");
Folder folder = (Folder) document.getFeature().get(0);
folder.setName("Mobile Phone Subscriptions 2008");

int folderSize = folder.getFeature().size();
// loop over all countries / Placemarks
for (int i = 0; i < folderSize; i++) {
  Placemark placemark = (Placemark) folder.getFeature().get(i);
  MultiGeometry multigeometry = (MultiGeometry) placemark.getGeometry();
  double height = -1;
  // only set height if data found in the HashMap (CSV)
  if (data.containsKey(placemark.getId())) {
    height = data.get(placemark.getId());
    placemark.withDescription("" + (int) height);
    // set a color gradient from yellow to red, calculating by the height, no transparency and no stroke/line
    Utils.setDataValueColor(placemark, max, height, "FF", 1, null, ColorMode.NORMAL);
    folder.addToFeature(placemark);
    // normalize height and add minimal polygon height to prevent the "polygon hole problem"
    height = ((height / max) * maxPolyHeight) + minPolyHeight;
  } else {
    // if no data found for the current country / Placemark, use no 3D polygon and set color to gray
    Utils.setPolyStyleAndLineStyle(placemark, "FFCCCCCC", ColorMode.NORMAL, 1, null, ColorMode.NORMAL);
    folder.addToFeature(placemark);
    placemark.withDescription("no data");
  }

  for (int j = 0; j < multigeometry.getGeometry().size(); j++) {
    Polygon polygon = (Polygon) multigeometry.getGeometry().get(j);
    if (height < 0) {
      // color overlay
      polygon.setAltitudeMode(AltitudeMode.CLAMP_TO_GROUND);
      polygon.setTessellate(Boolean.TRUE); // follow the terrain
    } else {
      // 3D polygon
      polygon.setAltitudeMode(AltitudeMode.RELATIVE_TO_GROUND); // altitude can only be set in this mode
      polygon.setExtrude(Boolean.TRUE); // connect to ground
    }

    // only for 3D polygons
    if (height > 0) {
      Boundary outerBoundaryIs = polygon.getOuterBoundaryIs();
      LinearRing linearRing = outerBoundaryIs.getLinearRing();
      List<Coordinate> coordinates = linearRing.getCoordinates();
      // set the altitude of all vertices (height of the polygon)
      for (Coordinate c : coordinates) {
        c.setAltitude(height);
      }
      // check enclaves or polygons like it
      if (!polygon.getInnerBoundaryIs().isEmpty()) {
        for (int k = 0; k < polygon.getInnerBoundaryIs().size(); k++) {
          Boundary innerBoundaryIs = polygon.getInnerBoundaryIs().get(k);
          LinearRing linearRingInner = innerBoundaryIs.getLinearRing();
          List<Coordinate> coordinatesInner = linearRingInner.getCoordinates();
          // set the altitude of all vertices (height of the polygon)
          for (Coordinate c : coordinatesInner) {
            c.setAltitude(height);
          }
        }
      }
    }
  }
}
unmarshal.marshal(new File("advancedexample3.kml"));

The full example is contained in JAK's sources (/JavaAPIforKML/src/test/java/de/micromata/jak/examples/Example3.java).

Navigate space

Java API for KML | @Google