Package org.geotools.coverage.processing.operation

Class Crop

  • All Implemented Interfaces:
    Serializable, Operation
    public class Crop
extends Operation2D
    The crop operation is responsible for selecting geographic subarea of the source coverage. The CoverageCrop operation does not merely wrap the JAI Crop operation but it goes beyond that as far as capabilities.

    The key point is that the CoverageCrop operation aims to perform a spatial crop, i.e. cropping the underlying raster by providing a spatial Bounds (if the envelope is not 2D only the 2D part of it will be used). This means that, depending on the grid-to-world transformation existing for the raster we want to crop, the crop area in the raster space might not be a rectangle, hence JAI's crop may not suffice in order to shrink the raster area we would obtain. For this purpose this operation make use of either the JAI's Crop or Mosaic operations depending on the conditions in which we are working.

    Meaning of the ROI_OPTIMISATION_TOLERANCE parameter
    In general if the grid-to-world transform is a simple scale and translate using JAI's crop should suffice, but when the g2w transform contains rotations or skew then we need something more elaborate since a rectangle in model space may not map to a rectangle in raster space. We would still be able to crop using JAI's crop on this polygon bounds but, depending on how this rectangle is built, we would be highly inefficient. In order to overcome this problems we use a combination of JAI's crop and mosaic since the mosaic can be used to crop a raster using a general ROI instead of a simple rectangle. There is a negative effect though. Crop would not create a new raster but simply forwards requests back to the original one (it basically create a viewport on the source raster) while the mosaic operation creates a new raster. We try to address this trade-off by providing the parameter ROI_OPTIMISATION_TOLERANCE, which basically tells this operation "Use the mosaic operation only if the area that we would load with the Mosaic is strictly smaller then (ROI_OPTIMISATION_TOLERANCE)* A' where A' is the area of the polygon resulting from converting the crop area from the model space to the raster space.

    ROI
    By providing a ROI parameter, the coverage can be cropped by any set of polygons, even disjuncted ones. When the ROI is provided, the JAI's Mosaic operation will be used.
    At least one between Envelope and ROI must be provided. If both of them are provided, the resulting area will be the intersection of them.
    ROI geometries must be in the same CRS as the source coverage.
    ROI must be any among a Polygon, a MultiPolygon, or a GeometryCollection of the two.

    NOTE that in case we will use the Mosaic operation with a ROI, such a ROI will be added as a synthetic property to the resulting coverage. The key for this property will be GC_ROI and the type of the object Polygon.

    Since:
    2.3
    Author:
    Simone Giannecchini (GeoSolutions), Emanuele Tajariol (GeoSolutions)
    See Also:
    CropDescriptor, Serialized Form