Mosaic Plugin

This format make use of a shapefile to act as a kind of index, the features in this shapefile list the filename of the “images” to display and the location in which they should be displayed.

Maven:

<dependency>
  <groupId>org.geotools</groupId>
  <artifactId>gt-imagemosaic</artifactId>
  <version>${geotools.version}</version>
</dependency>

To create the shapefile you simply provide the location of a folder with “images” to the constructor of ImageMosaicReader. Those image files must conatin it’s own world-file to be a part of the image mosaic.

To display the mosaic within a map, you will use a GridReaderLayer.

            ImageMosaicReader reader = new ImageMosaicReader(new File(pathMosaic));
            layer = new GridReaderLayer(reader, style);

The simplest style to provide would be like this:

        Style style = styleFactory.createStyle();

        FeatureTypeStyle type = styleFactory.createFeatureTypeStyle();
        style.featureTypeStyles().add(type);

        Rule rule = styleFactory.createRule();
        rule.symbolizers().add(styleFactory.createRasterSymbolizer());

        type.rules().add(rule);

To use mulitthreading you must provide a threading pool to the mosaic reader, and also tell the grid reader layer to allow multithreading.

            ExecutorService executor = Executors.newFixedThreadPool(numThreads);

            ImageMosaicReader reader =
                    new ImageMosaicReader(new File(pathMosaic), new Hints(Hints.EXECUTOR_SERVICE, executor));

            ParameterValue<Boolean> multithreadParam = ImageMosaicFormat.ALLOW_MULTITHREADING.createValue();
            multithreadParam.setValue(true);

            layer = new GridReaderLayer(reader, style, new GeneralParameterValue[] {multithreadParam});

Example Image Mosaic files

An example data set looks something like:

bluemarble.shp
bluemarble.prj
bluemarble.properties
sample_image.dat
... a bunch of raster files ...

  • Shapefile file

    The schema of your shapefile is important:

    You MUST have a attribute called “location”, this will be used to look up the raster files

  • PRJ file

    The usual projection file associated with a shapefile, using the WKT format for a CoordinateReferenceSystem.

  • Sample image file

    The sample_image.dat (legacy sample_image) is a sample image used to determine color model upfront without requiring a full scan.

    By default the sample image file is limited to built-in image formats and color models. The old sample image file format that used the javax.media.jai.remote.SerializableRenderedImage class is also blocked by default. This restriction may be relaxed using the system property org.geotools.gce.imagemosaic.sampleimage.allowlist:

    org.geotools.gce.imagemosaic.sampleimage.allowlist=^java\\.(net\\.InetAddress|util\\.Hashtable)$

  • Properties File

    The property file is REQUIRED and use to provide a bunch of settings:

    Example bluemarble.properties:

    #
#Thu Jan 11 14:53:30 CET 2007
Name=modis
ExpandToRGB=true
Levels=10000.0,10000.0
LevelsNum=1
GeneralBounds=-3637013.0,-1158091.0 1019969.0,4092819.0
NumFiles=3

    Where the following are required:

    • Name

    • ExpandToRGB: true if we need to expand the color model from indexed to rgba

      • If all your images use the same indexed palette you can set this to false and get a large performance gain

    • Levels: list of resolutions

      • Format: level_0_x_resolution, level_0_y_resolution, level_1_x_resolution, level_1_y_resolution

      • This measure of resolution describes how big each pixel is in real world units

      • Sample calculation: envelope.getLength(0) / image.getWidth()

      • You can define several levels in order to capture overview files if you have them

    • LevelsNum: the number of levels mentioned above

    • GeneralBounds: bounds in the CRS specified in the .prj file

    • Format: minX,minY maxX,maxY

    • NumFiles: should be the same as the number of features in your shapefile

Reference