Pregenerating tiled images for a thin client
The
IlvManagerTiler class is a utility class that renders a map, saved to a specified location on the disk at different scale levels, as tiled images. These images can be used to fill the cache of a thin-client server application. Offline tile generation speeds up the initial response time of the server, as it does not need to create and cache the images when clients request them. It increases the server scalability for the same reason.
The first step to generate tiled images for a map is to ensure that the Thin Client Parameters have been set in the map, see
Setting Thin Client Parameters in
JViews Maps Using the Map Builder. What the map builder does is that is to add two
IlvNamedProperty instances to the map. The names of these properties are defined in the IlvMapTileGen
IlvMapTileGeneratorConstants class as constants:
TILE_SIZE_PROPERTY is the name of the property that holds the size of the tiles that will be generated. The size is measure in pixels. An example value is 256 pixels.
SCALE_LEVELS_PROPERTY PROPERTY is the name of the property that holds an array of
double values representing the different scales at which the map should be rendered using tiles.
If these parameters are not set in the map, you must specify them explicitly in the
createTiles() method call. Then, you must create an
IlvManagerTiler instance and call the
createTiles method with the appropriate parameters using the following code:
IlvManagerTiler tiler = new IlvManagerTiler();
long maximumDiskSpace = 10000000; // 10 Mbytes
String mapFilename = "MyMap.ivl";
File outputFolder = new File("output");
tiler.createTiles(mapFilename,null, outputFolder, maximumDiskSpace);
// Null is passed as the region so as not to limit the tiling process.
Remember that generating tiles for a map covering a large region, with several scale levels, and without specifying an area of interest, can easily lead to millions of tiles being created. This may require several Gigabytes of memory and in some cases may take a long time to complete.
To avoid this:
Specify a reasonable disk space limit. The process stops as soon as the limit is reached.
and/or
Target regions that are likely to be requested by thin clients and only generate images for these regions.
A graphical tool to interactively generate tiles is provided as a code sample in:
<installdir> /jviews-maps/samples/tilegeneration/src/TileGenerator.java.
NOTE Only map layers with the thin client background property set to true in their style will be rendered as tiled images. Dynamic layers such as labeling layers should not be marked as background layers, as they are dynamically generated by the servlet.
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