com.vividsolutions.jts.geom.PrecisionModel Maven / Gradle / Ivy
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/*
* The JTS Topology Suite is a collection of Java classes that
* implement the fundamental operations required to validate a given
* geo-spatial data set to a known topological specification.
*
* Copyright (C) 2001 Vivid Solutions
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*
* For more information, contact:
*
* Vivid Solutions
* Suite #1A
* 2328 Government Street
* Victoria BC V8T 5G5
* Canada
*
* (250)385-6040
* www.vividsolutions.com
*/
package com.vividsolutions.jts.geom;
import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;
/**
* Specifies the precision model of the {@link Coordinate}s in a {@link Geometry}.
* In other words, specifies the grid of allowable
* points for all Geometrys.
*
* The {@link #makePrecise(Coordinate)} method allows rounding a coordinate to
* a "precise" value; that is, one whose
* precision is known exactly.
*
* Coordinates are assumed to be precise in geometries.
* That is, the coordinates are assumed to be rounded to the
* precision model given for the geometry.
* JTS input routines automatically round coordinates to the precision model
* before creating Geometries.
* All internal operations
* assume that coordinates are rounded to the precision model.
* Constructive methods (such as boolean operations) always round computed
* coordinates to the appropriate precision model.
*
* Currently three types of precision model are supported:
*
* - FLOATING - represents full double precision floating point.
* This is the default precision model used in JTS
*
- FLOATING_SINGLE - represents single precision floating point.
*
- FIXED - represents a model with a fixed number of decimal places.
* A Fixed Precision Model is specified by a scale factor.
* The scale factor specifies the size of the grid which numbers are rounded to.
* Input coordinates are mapped to fixed coordinates according to the following
* equations:
*
* - jtsPt.x = round( (inputPt.x * scale ) / scale
*
- jtsPt.y = round( (inputPt.y * scale ) / scale
*
*
* For example, to specify 3 decimal places of precision, use a scale factor
* of 1000. To specify -3 decimal places of precision (i.e. rounding to
* the nearest 1000), use a scale factor of 0.001.
*
* Coordinates are represented internally as Java double-precision values.
* Since Java uses the IEEE-394 floating point standard, this
* provides 53 bits of precision. (Thus the maximum precisely representable
* integer is 9,007,199,254,740,992 - or almost 16 decimal digits of precision).
*
* JTS binary methods currently do not handle inputs which have different precision models.
* The precision model of any constructed geometric value is undefined.
*
*@version 1.7
*/
public class PrecisionModel implements Serializable, Comparable
{
/**
* Determines which of two {@link PrecisionModel}s is the most precise
* (allows the greatest number of significant digits).
*
* @param pm1 a PrecisionModel
* @param pm2 a PrecisionModel
* @return the PrecisionModel which is most precise
*/
public static PrecisionModel mostPrecise(PrecisionModel pm1, PrecisionModel pm2)
{
if (pm1.compareTo(pm2) >= 0)
return pm1;
return pm2;
}
private static final long serialVersionUID = 7777263578777803835L;
/**
* The types of Precision Model which JTS supports.
*/
public static class Type
implements Serializable
{
private static final long serialVersionUID = -5528602631731589822L;
private static Map nameToTypeMap = new HashMap();
public Type(String name) {
this.name = name;
nameToTypeMap.put(name, this);
}
private String name;
public String toString() { return name; }
/*
* Ssee http://www.javaworld.com/javaworld/javatips/jw-javatip122.html
*/
private Object readResolve() {
return nameToTypeMap.get(name);
}
}
/**
* Fixed Precision indicates that coordinates have a fixed number of decimal places.
* The number of decimal places is determined by the log10 of the scale factor.
*/
public static final Type FIXED = new Type("FIXED");
/**
* Floating precision corresponds to the standard Java
* double-precision floating-point representation, which is
* based on the IEEE-754 standard
*/
public static final Type FLOATING = new Type("FLOATING");
/**
* Floating single precision corresponds to the standard Java
* single-precision floating-point representation, which is
* based on the IEEE-754 standard
*/
public static final Type FLOATING_SINGLE = new Type("FLOATING SINGLE");
/**
* The maximum precise value representable in a double. Since IEE754
* double-precision numbers allow 53 bits of mantissa, the value is equal to
* 2^53 - 1. This provides almost 16 decimal digits of precision.
*/
public final static double maximumPreciseValue = 9007199254740992.0;
/**
* The type of PrecisionModel this represents.
*/
private Type modelType;
/**
* The scale factor which determines the number of decimal places in fixed precision.
*/
private double scale;
/**
* Creates a PrecisionModel with a default precision
* of FLOATING.
*/
public PrecisionModel() {
// default is floating precision
modelType = FLOATING;
}
/**
* Creates a PrecisionModel that specifies
* an explicit precision model type.
* If the model type is FIXED the scale factor will default to 1.
*
* @param modelType the type of the precision model
*/
public PrecisionModel(Type modelType)
{
this.modelType = modelType;
if (modelType == FIXED)
{
setScale(1.0);
}
}
/**
* Creates a PrecisionModel that specifies Fixed precision.
* Fixed-precision coordinates are represented as precise internal coordinates,
* which are rounded to the grid defined by the scale factor.
*
*@param scale amount by which to multiply a coordinate after subtracting
* the offset, to obtain a precise coordinate
*@param offsetX not used.
*@param offsetY not used.
*
* @deprecated offsets are no longer supported, since internal representation is rounded floating point
*/
public PrecisionModel(double scale, double offsetX, double offsetY) {
modelType = FIXED;
setScale(scale);
}
/**
* Creates a PrecisionModel that specifies Fixed precision.
* Fixed-precision coordinates are represented as precise internal coordinates,
* which are rounded to the grid defined by the scale factor.
*
*@param scale amount by which to multiply a coordinate after subtracting
* the offset, to obtain a precise coordinate
*/
public PrecisionModel(double scale) {
modelType = FIXED;
setScale(scale);
}
/**
* Copy constructor to create a new PrecisionModel
* from an existing one.
*/
public PrecisionModel(PrecisionModel pm) {
modelType = pm.modelType;
scale = pm.scale;
}
/**
* Tests whether the precision model supports floating point
* @return true if the precision model supports floating point
*/
public boolean isFloating()
{
return modelType == FLOATING || modelType == FLOATING_SINGLE;
}
/**
* Returns the maximum number of significant digits provided by this
* precision model.
* Intended for use by routines which need to print out
* decimal representations of precise values (such as {@link WKTWriter}).
*
* This method would be more correctly called
* getMinimumDecimalPlaces,
* since it actually computes the number of decimal places
* that is required to correctly display the full
* precision of an ordinate value.
*
* Since it is difficult to compute the required number of
* decimal places for scale factors which are not powers of 10,
* the algorithm uses a very rough approximation in this case.
* This has the side effect that for scale factors which are
* powers of 10 the value returned is 1 greater than the true value.
*
*
* @return the maximum number of decimal places provided by this precision model
*/
public int getMaximumSignificantDigits() {
int maxSigDigits = 16;
if (modelType == FLOATING) {
maxSigDigits = 16;
} else if (modelType == FLOATING_SINGLE) {
maxSigDigits = 6;
} else if (modelType == FIXED) {
maxSigDigits = 1 + (int) Math.ceil(Math.log(getScale()) / Math.log(10));
}
return maxSigDigits;
}
/**
* Returns the scale factor used to specify a fixed precision model.
* The number of decimal places of precision is
* equal to the base-10 logarithm of the scale factor.
* Non-integral and negative scale factors are supported.
* Negative scale factors indicate that the places
* of precision is to the left of the decimal point.
*
*@return the scale factor for the fixed precision model
*/
public double getScale() {
return scale;
}
/**
* Gets the type of this precision model
* @return the type of this precision model
* @see Type
*/
public Type getType()
{
return modelType;
}
/**
* Sets the multiplying factor used to obtain a precise coordinate.
* This method is private because PrecisionModel is an immutable (value) type.
*/
private void setScale(double scale)
{
this.scale = Math.abs(scale);
}
/**
* Returns the x-offset used to obtain a precise coordinate.
*
* @return the amount by which to subtract the x-coordinate before
* multiplying by the scale
* @deprecated Offsets are no longer used
*/
public double getOffsetX() {
//We actually don't use offsetX and offsetY anymore ... [Jon Aquino]
return 0;
}
/**
* Returns the y-offset used to obtain a precise coordinate.
*
* @return the amount by which to subtract the y-coordinate before
* multiplying by the scale
* @deprecated Offsets are no longer used
*/
public double getOffsetY() {
return 0;
}
/**
* Sets internal to the precise representation of external.
*
* @param external the original coordinate
* @param internal the coordinate whose values will be changed to the
* precise representation of external
* @deprecated use makePrecise instead
*/
public void toInternal (Coordinate external, Coordinate internal) {
if (isFloating()) {
internal.x = external.x;
internal.y = external.y;
}
else {
internal.x = makePrecise(external.x);
internal.y = makePrecise(external.y);
}
internal.z = external.z;
}
/**
* Returns the precise representation of external.
*
*@param external the original coordinate
*@return the coordinate whose values will be changed to the precise
* representation of external
* @deprecated use makePrecise instead
*/
public Coordinate toInternal(Coordinate external) {
Coordinate internal = new Coordinate(external);
makePrecise(internal);
return internal;
}
/**
* Returns the external representation of internal.
*
*@param internal the original coordinate
*@return the coordinate whose values will be changed to the
* external representation of internal
* @deprecated no longer needed, since internal representation is same as external representation
*/
public Coordinate toExternal(Coordinate internal) {
Coordinate external = new Coordinate(internal);
return external;
}
/**
* Sets external to the external representation of internal.
*
*@param internal the original coordinate
*@param external the coordinate whose values will be changed to the
* external representation of internal
* @deprecated no longer needed, since internal representation is same as external representation
*/
public void toExternal(Coordinate internal, Coordinate external) {
external.x = internal.x;
external.y = internal.y;
}
/**
* Rounds a numeric value to the PrecisionModel grid.
* Asymmetric Arithmetic Rounding is used, to provide
* uniform rounding behaviour no matter where the number is
* on the number line.
*
* This method has no effect on NaN values.
*
* Note: Java's Math#rint uses the "Banker's Rounding" algorithm,
* which is not suitable for precision operations elsewhere in JTS.
*/
public double makePrecise(double val)
{
// don't change NaN values
if (Double.isNaN(val)) return val;
if (modelType == FLOATING_SINGLE) {
float floatSingleVal = (float) val;
return (double) floatSingleVal;
}
if (modelType == FIXED) {
return Math.round(val * scale) / scale;
// return Math.rint(val * scale) / scale;
}
// modelType == FLOATING - no rounding necessary
return val;
}
/**
* Rounds a Coordinate to the PrecisionModel grid.
*/
public void makePrecise(Coordinate coord)
{
// optimization for full precision
if (modelType == FLOATING) return;
coord.x = makePrecise(coord.x);
coord.y = makePrecise(coord.y);
//MD says it's OK that we're not makePrecise'ing the z [Jon Aquino]
}
public String toString() {
String description = "UNKNOWN";
if (modelType == FLOATING) {
description = "Floating";
} else if (modelType == FLOATING_SINGLE) {
description = "Floating-Single";
} else if (modelType == FIXED) {
description = "Fixed (Scale=" + getScale() + ")";
}
return description;
}
public boolean equals(Object other) {
if (! (other instanceof PrecisionModel)) {
return false;
}
PrecisionModel otherPrecisionModel = (PrecisionModel) other;
return modelType == otherPrecisionModel.modelType
&& scale == otherPrecisionModel.scale;
}
/**
* Compares this {@link PrecisionModel} object with the specified object for order.
* A PrecisionModel is greater than another if it provides greater precision.
* The comparison is based on the value returned by the
* {@link #getMaximumSignificantDigits} method.
* This comparison is not strictly accurate when comparing floating precision models
* to fixed models; however, it is correct when both models are either floating or fixed.
*
*@param o the PrecisionModel with which this PrecisionModel
* is being compared
*@return a negative integer, zero, or a positive integer as this PrecisionModel
* is less than, equal to, or greater than the specified PrecisionModel
*/
public int compareTo(Object o) {
PrecisionModel other = (PrecisionModel) o;
int sigDigits = getMaximumSignificantDigits();
int otherSigDigits = other.getMaximumSignificantDigits();
return (new Integer(sigDigits)).compareTo(new Integer(otherSigDigits));
// if (sigDigits > otherSigDigits)
// return 1;
// else if
// if (modelType == FLOATING && other.modelType == FLOATING) return 0;
// if (modelType == FLOATING && other.modelType != FLOATING) return 1;
// if (modelType != FLOATING && other.modelType == FLOATING) return -1;
// if (modelType == FIXED && other.modelType == FIXED) {
// if (scale > other.scale)
// return 1;
// else if (scale < other.scale)
// return -1;
// else
// return 0;
// }
// Assert.shouldNeverReachHere("Unknown Precision Model type encountered");
// return 0;
}
}