org.geotools.referencing.operation.transform
Class LocalizationGrid

java.lang.Object
  org.geotools.referencing.operation.transform.LocalizationGrid

public class LocalizationGrid

extends java.lang.Object

A factory for MathTransform2D backed by a grid of localization. A grid of localization is a two-dimensional array of coordinate points. The grid size is × . Input coordinates are (i,j) index in the grid, where i must be in the range and j in the range inclusive. Output coordinates are the values stored in the grid of localization at the specified index.

The class is usefull when the "grid to coordinate system" transform for a coverage is not some kind of global mathematical relationship like an affine transform. Instead, the "real world" coordinates are explicitly specified for each pixels. If the real world coordinates are know only for some pixels at a fixed interval, then a transformation can be constructed by the concatenation of an affine transform with a grid of localization.

After a object has been fully constructed (i.e. real world coordinates have been specified for all grid cells), a transformation from grid coordinates to "real world" coordinates can be obtained with the getMathTransform() method. If this transformation is close enough to an affine transform, then an instance of AffineTransform is returned. Otherwise, a transform backed by the localization grid is returned.

The example below goes through the steps of constructing a coordinate reference system for a grid coverage from its grid of localization. This example assumes that the "real world" coordinates are longitudes and latitudes on the WGS84 ellipsoid.

 //
 // Constructs a localization grid of size 10×10.
 //
 LocalizationGrid grid = new LocalizationGrid(10,10);
 for (int j=0; j<10; j++) {
     for (int i=0; i<10; i++) {
         double x = ...; // Set longitude here
         double y = ...; // Set latitude here
         grid.setLocalizationPoint(i,j,x,y);
     }
 }
 //
 // Constructs the grid coordinate reference system. degree is the polynomial
 // degree (e.g. 2) for a math transform that approximately map the grid of localization.
 // For a more accurate (but not always better) math transform backed by the whole grid,
 // invokes getMathTransform() instead, or use the special value of 0 for the degree
 // argument.
 //
 MathTransform2D        realToGrid = grid.getPolynomialTransform(degree).inverse();
 CoordinateReferenceSystem realCRS = DefaultGeographicCRS.WGS84;
 CoordinateReferenceSystem gridCRS = new DefaultDerivedCRS("The grid CRS",
         new DefaultOperationMethod(realToGrid),
         realCRS,     // The target ("real world") CRS
         realToGrid,  // How the grid CRS relates to the "real world" CRS
         DefaultCartesianCS.GRID);

 //
 // Constructs the grid coverage using the grid coordinate system (not the "real world"
 // one). It is usefull to display the coverage in its native CRS before we resample it.
 // Note that if the grid of localization does not define the geographic location for
 // all pixels, then we need to specify some affine transform in place of the call to
 // IdentityTransform. For example if the grid of localization defines the location of
 // 1 pixel, then skip 3, then defines the location of 1 pixel, etc., then the affine
 // transform should be AffineTransform.getScaleInstance(0.25, 0.25).
 //
 WritableRaster raster = RasterFactory.createBandedRaster(DataBuffer.TYPE_FLOAT,
                                                          width, height, 1, null);
 for (int y=0; ysome_value);
     }
 }
 GridCoverageFactory factory = FactoryFinder.getGridCoverageFactory(null);
 GridCoverage coverage = factory.create("My grayscale coverage", raster, gridCRS,
                          IdentityTransform.create(2), null, null, null, null, null);
 coverage.show();
 //
 // Projects the coverage from its current 'gridCS' to the 'realCS'. If the grid of
 // localization was built from the orbit of some satellite, then the projected
 // coverage will tpypically have a curved aspect.
 //
 coverage = (Coverage2D) Operations.DEFAULT.resample(coverage, realCRS);
 coverage.show();
 

Since:

2.0

Version:

$Id: LocalizationGrid.java 17672 2006-01-19 00:25:55Z desruisseaux $

Author:

Remi Eve, Martin Desruisseaux, Alessio Fabiani

See Also:

DerivedCRS

Constructor Summary

LocalizationGrid(int width, int height)
Constructs an initially empty localization grid.

Method Summary

java.awt.geom.AffineTransform	getAffineTransform() Returns an affine transform for the whole grid.
java.awt.geom.Point2D	getLocalizationPoint(java.awt.Point source) Returns the "real world" coordinates for the specified grid coordinates.
org.opengis.referencing.operation.MathTransform2D	getMathTransform() Returns a math transform from grid to "real world" coordinates.
org.opengis.referencing.operation.MathTransform2D	getPolynomialTransform(int degree) Returns a math transform from grid to "real world" coordinates using a polynomial fitting of the specified degree.
java.awt.Dimension	getSize() Returns the grid size.
boolean	isMonotonic(boolean strict) Returns if all coordinates in this grid are increasing or decreasing.
boolean	isNaN() Returns if this localization grid contains at least one value.
void	removeSingularities() Makes sure that the grid doesn't contains identical consecutive ordinates.
void	setLocalizationPoint(int sourceX, int sourceY, double targetX, double targetY) Set a point in this localization grid.
void	setLocalizationPoint(java.awt.Point source, java.awt.geom.Point2D target) Set a point in this localization grid.
void	transform(java.awt.geom.AffineTransform transform, java.awt.Rectangle region) Apply a transformation to every "real world" coordinate points in a sub-region of this grid.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

LocalizationGrid

public LocalizationGrid(int width,
                        int height)

Constructs an initially empty localization grid. All "real worlds" coordinates are initially set to .

Parameters:

width - Number of grid's columns.

height - Number of grid's rows.

Method Detail

getSize

public java.awt.Dimension getSize()

Returns the grid size. Grid coordinates are always in the range xinput = [0..width-1] and yinput = [0..height-1] inclusive.

getLocalizationPoint

public java.awt.geom.Point2D getLocalizationPoint(java.awt.Point source)

Returns the "real world" coordinates for the specified grid coordinates. Grid coordinates must be integers inside this grid's range. For general transformations involving non-integer grid coordinates and/or coordinates outside this grid's range, use getMathTransform() instead.

Parameters:

source - The point in grid coordinates.

Returns:

target The corresponding point in "real world" coordinates.

Throws:

java.lang.IndexOutOfBoundsException - If the source point is not in this grid's range.

setLocalizationPoint

public void setLocalizationPoint(java.awt.Point source,
                                 java.awt.geom.Point2D target)

Set a point in this localization grid.

Parameters:

source - The point in grid coordinates.

target - The corresponding point in "real world" coordinates.

Throws:

java.lang.IndexOutOfBoundsException - If the source point is not in this grid's range.

setLocalizationPoint

public void setLocalizationPoint(int sourceX,
                                 int sourceY,
                                 double targetX,
                                 double targetY)

Set a point in this localization grid.

Parameters:

sourceX - x coordinates in grid coordinates, in the range inclusive.

sourceY - y coordinates in grid coordinates. in the range inclusive.

targetX - x coordinates in "real world" coordinates.

targetY - y coordinates in "real world" coordinates.

Throws:

java.lang.IndexOutOfBoundsException - If the source coordinates is not in this grid's range.

transform

public void transform(java.awt.geom.AffineTransform transform,
                      java.awt.Rectangle region)

Apply a transformation to every "real world" coordinate points in a sub-region of this grid.

Parameters:

transform - The transform to apply.

region - The bounding rectangle (in grid coordinate) for region where to apply the transform, or to transform the whole grid.

isNaN

public boolean isNaN()

Returns if this localization grid contains at least one value.

isMonotonic

public boolean isMonotonic(boolean strict)

Returns if all coordinates in this grid are increasing or decreasing. More specifically, returns if the following conditions are meets:

• Coordinates in a row must be increasing or decreasing. If is , then coordinates must be strictly increasing or decreasing (i.e. equals value are not accepted). values are always ignored.
• Coordinates in all rows must be increasing, or coordinates in all rows must be decreasing.
• Idem for columns (Coordinates in a columns must be increasing or decreasing, etc.).

x and y coordinates are tested independently.

Parameters:

strict - to require strictly increasing or decreasing order, or to accept values that are equals.

Returns:

if coordinates are increasing or decreasing in the same direction for all rows and columns.

removeSingularities

public void removeSingularities()

Makes sure that the grid doesn't contains identical consecutive ordinates. If many consecutives ordinates are found to be identical in a row or in a column, then the first one is left inchanged and the other ones are linearly interpolated.

getAffineTransform

public java.awt.geom.AffineTransform getAffineTransform()

Returns an affine transform for the whole grid. This transform is only an approximation for this localization grid. It is fitted (like "curve fitting") to grid data using the "least squares" method.

Returns:

A global affine transform as an approximation for the whole localization grid.

getPolynomialTransform

public org.opengis.referencing.operation.MathTransform2D getPolynomialTransform(int degree)

Returns a math transform from grid to "real world" coordinates using a polynomial fitting of the specified degree. By convention, a of 0 will returns the math transform backed by the whole grid. Greater values will use a fitted polynomial (affine transform for degree 1, quadratic transform for degree 2, cubic transform for degree 3, etc.).

Parameters:

degree - The polynomial degree for the fitting, or 0 for a transform backed by the whole grid.

getMathTransform

public final org.opengis.referencing.operation.MathTransform2D getMathTransform()

Returns a math transform from grid to "real world" coordinates. The math transform is backed by the full grid of localization. In terms of JAI's image warp operations, this math transform is backed by a WarpGrid while the previous methods return math transforms backed by WarpPolynomial.