org.geotools.renderer.geom
Class CompressionLevel

java.lang.Object
  javax.media.jai.EnumeratedParameter
      org.geotools.renderer.geom.CompressionLevel

All Implemented Interfaces:

java.io.Serializable

public final class CompressionLevel

extends javax.media.jai.EnumeratedParameter

The compression level for coordinate points in a Geometry object. Compressions are trigged by the Geometry.compress(...) method and consist in a change of the storage type for (x,y) coordinates. Note that the compression may be destructive, i.e. it may sacrifice data and/or precision. For example, JTS 1.3 stores points as Coordinate objects with (x,y,z) double values, which consume a lot of memory. The compression level DIRECT_AS_FLOATS recopies the (x,y) ordinates in a float[] array, loosing the z value and some precision due to the conversion of double to float values. The compression level RELATIVE_AS_BYTES goes further with a two steps process:

• First, it invokes setResolution(dx + 0.5*std) where dx is the geometry mean resolution and std is the resolution's standard deviation. This call ensure that distance between each consecutive points is approximatively constant and long enough for 2/3 of line segments (i.e. this resampling may add new points for less than 1/3 of line segments, assuming a normal (gaussian) distribution). If a different resampling is wanted, just invoke setResolution(...) explicitely before compress(...).

• Second, it replaces absolute positions (left handed image) by relative positions (right handed image), i.e. distances relative to the previous point. Since all distances are of similar magnitude, distances can be coded in byte primitive type instead of float.

Version:

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

Author:

Martin Desruisseaux

See Also:

Geometry.compress(org.geotools.renderer.geom.CompressionLevel), Serialized Form

Field Summary

static CompressionLevel	DIRECT_AS_FLOATS Transform coordinate points into direct positions stored as float values.
static CompressionLevel	RELATIVE_AS_BYTES Transform coordinate points into relative positions stored as byte values.

Methods inherited from class javax.media.jai.EnumeratedParameter

equals, getName, getValue, hashCode, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

DIRECT_AS_FLOATS

public static final CompressionLevel DIRECT_AS_FLOATS

Transform coordinate points into direct positions stored as float values. This compression level has no effect if data are already stored as float, or if a more agressive compression is already in use (e.g. RELATIVE_AS_BYTES).

RELATIVE_AS_BYTES

public static final CompressionLevel RELATIVE_AS_BYTES

Transform coordinate points into relative positions stored as byte values. Before the compression, the coordinates are resampled (if needed) in order to obtain line segments of equal length. This compression level has no effect if the data are already compressed as relative positions.