org.geotools.geometry.jts

Class Decimator

Object

Decimator

public final class Decimator
extends Object

Accepts geometries and collapses all the vertices that will be rendered to the same pixel. This class works only if the Geometries are based on LiteCoordinateSequence instances.

Since:

2.1.x

Author:

jeichar

Constructor Summary

Constructors

Constructor and Description
Decimator(double spanx, double spany)
Decimator(MathTransform screenToWorld) Deprecated. use the other constructor (with rectange) see javadox. This works fine, but it the results are often poor if you're also doing CRS xforms.
Decimator(MathTransform screenToWorld, Rectangle paintArea) djb - noticed that the old way of finding out the decimation is based on the (0,0) location of the image.
Decimator(MathTransform screenToWorld, Rectangle paintArea, double pixelDistance) Builds a decimator that will generalize geometries so that two subsequent points will be at least pixelDistance away from each other when painted on the screen.

Method Summary

Modifier and Type	Method and Description
static double[]	computeGeneralizationDistances(MathTransform screenToWorld, Rectangle paintArea, double pixelDistance) Given a full transformation from screen to world and the paint area computes a best guess of the maxium generalization distance that won't make the transformations induced by the generalization visible on screen.
void	decimate(Geometry geom) decimates JTS geometries.
Geometry	decimateTransformGeneralize(Geometry geometry, MathTransform transform)
double	getSpanX() The generalization step in the x direction
double	getSpanY() The generalization step in the y direction

Methods inherited from class Object

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

Constructor Detail

Decimator

public Decimator(MathTransform screenToWorld,
                 Rectangle paintArea,
                 double pixelDistance)

Builds a decimator that will generalize geometries so that two subsequent points will be at least pixelDistance away from each other when painted on the screen. Set pixelDistance to 0 if you don't want any generalization (but just a transformation)

Parameters:

screenToWorld -

paintArea -

pixelDistance -

Decimator

public Decimator(MathTransform screenToWorld,
                 Rectangle paintArea)

djb - noticed that the old way of finding out the decimation is based on the (0,0) location of the image. This is often wildly unrepresentitive of the scale of the entire map.

A better thing to do is to decimate this on a per-shape basis (and use the shape's center). Another option would be to sample the image at different locations (say 9) and choose the smallest spanx/spany you find.

Also, if the xform is an affine Xform, you can be a bit more aggressive in the decimation. If its not an affine xform (ie. its actually doing a CRS xform), you may find this is a bit too aggressive due to any number of mathematical issues.

This is just a simple method that uses the centre of the given rectangle instead of (0,0).

NOTE: this could need more work based on CRS, but the rectangle is in pixels so it should be fairly immune to all but crazy projections.

Parameters:

screenToWorld -

paintArea -

Decimator

public Decimator(MathTransform screenToWorld)

Deprecated. use the other constructor (with rectange) see javadox. This works fine, but it the results are often poor if you're also doing CRS xforms.

Throws:

TransformException

Decimator

public Decimator(double spanx,
                 double spany)

Method Detail

getSpanX

public double getSpanX()

The generalization step in the x direction

getSpanY

public double getSpanY()

The generalization step in the y direction

computeGeneralizationDistances

public static double[] computeGeneralizationDistances(MathTransform screenToWorld,
                                                      Rectangle paintArea,
                                                      double pixelDistance)
                                               throws TransformException

Given a full transformation from screen to world and the paint area computes a best guess of the maxium generalization distance that won't make the transformations induced by the generalization visible on screen.

In other words, it computes how long a pixel is in the native spatial reference system of the data

Parameters:

screenToWorld -

paintArea -

Returns:

Throws:

TransformException

decimateTransformGeneralize

public final Geometry decimateTransformGeneralize(Geometry geometry,
                                                  MathTransform transform)
                                           throws TransformException

Throws:

TransformException

decimate

public final void decimate(Geometry geom)

decimates JTS geometries.