bufferop.h

在Linux下做的QuadTree的程序

/**********************************************************************
 * $Id: BufferOp.h 1969 2007-02-06 01:57:23Z strk $
 *
 * GEOS - Geometry Engine Open Source
 * http://geos.refractions.net
 *
 * Copyright (C) 2006 Refractions Research Inc.
 *
 * This is free software; you can redistribute and/or modify it under
 * the terms of the GNU Lesser General Public Licence as published
 * by the Free Software Foundation. 
 * See the COPYING file for more information.
 *
 **********************************************************************/

#ifndef GEOS_OP_BUFFER_BUFFEROP_H
#define GEOS_OP_BUFFER_BUFFEROP_H

#include <geos/operation/buffer/OffsetCurveBuilder.h> // for enum values 
#include <geos/util/TopologyException.h> // for composition

// Forward declarations
namespace geos {
	namespace geom {
		class PrecisionModel;
		class Geometry;
	}
}

namespace geos {
namespace operation { // geos.operation
namespace buffer { // geos.operation.buffer

/**
 * \class BufferOp opBuffer.h geos/opBuffer.h
 *
 * \brief
 * Computes the buffer of a geometry, for both positive and negative
 * buffer distances.
 *
 * In GIS, the buffer of a geometry is defined as
 * the Minkowski sum or difference of the geometry
 * with a circle with radius equal to the absolute value of the buffer
 * distance.
 * In the CAD/CAM world buffers are known as </i>offset curves</i>.
 * In morphological analysis they are known as <i>erosion</i> and <i>dilation</i>.
 *
 * The buffer operation always returns a polygonal result.
 * The negative or zero-distance buffer of lines and points is always an empty Polygon.
 * 
 * Since true buffer curves may contain circular arcs,
 * computed buffer polygons can only be approximations to the true geometry.
 * The user can control the accuracy of the curve approximation by specifying
 * the number of linear segments with which to approximate a curve.
 * 
 * The end cap style of a linear buffer may be specified.
 * The following end cap styles are supported:
 * - CAP_ROUND - the usual round end caps
 * - CAP_BUTT - end caps are truncated flat at the line ends
 * - CAP_SQUARE - end caps are squared off at the buffer distance
 *   beyond the line ends
 * 
 * Last port: operation/buffer/BufferOp.java rev. 1.31 (JTS-1.7)
 *
 */
class BufferOp {


private:

	/**
	 *  A number of digits of precision which leaves some computational "headroom"
	 *  for floating point operations.
	 * 
	 *  This value should be less than the decimal precision of double-precision values (16).
	 */
	static const int MAX_PRECISION_DIGITS = 12;

	/**
	 * Compute a reasonable scale factor to limit the precision of
	 * a given combination of Geometry and buffer distance.
	 * The scale factor is based on a heuristic.
	 *
	 * @param g the Geometry being buffered
	 *
	 * @param distance the buffer distance
	 *
	 * @param maxPrecisionDigits the mzx # of digits that should be
	 *        allowed by the precision determined by the
	 *        computed scale factor
	 *
	 * @return a scale factor that allows a reasonable amount of
	 *         precision for the buffer computation
	 */
	static double precisionScaleFactor(const geom::Geometry *g,
			double distance, int maxPrecisionDigits);

	const geom::Geometry *argGeom;

	util::TopologyException saveException;

	double distance;

	int quadrantSegments;

	int endCapStyle;

	geom::Geometry* resultGeometry;

	void computeGeometry();

	void bufferOriginalPrecision();

	void bufferReducedPrecision(int precisionDigits);

	void bufferReducedPrecision();

	void bufferFixedPrecision(const geom::PrecisionModel& fixedPM);

public:

	enum {
		/// Specifies a round line buffer end cap style.
		CAP_ROUND,
		/// Specifies a butt (or flat) line buffer end cap style.
		CAP_BUTT,
		/// Specifies a square line buffer end cap style.
		CAP_SQUARE
	};

	/**
	 * Computes the buffer for a geometry for a given buffer distance
	 * and accuracy of approximation.
	 *
	 * @param g the geometry to buffer
	 * @param distance the buffer distance
	 * @param quadrantSegments the number of segments used to
	 *        approximate a quarter circle
	 * @return the buffer of the input geometry
	 *
	 */
	static geom::Geometry* bufferOp(const geom::Geometry *g,
		double distance,
		int quadrantSegments=
			OffsetCurveBuilder::DEFAULT_QUADRANT_SEGMENTS,
		int endCapStyle=BufferOp::CAP_ROUND);

	/**
	 * Initializes a buffer computation for the given geometry
	 *
	 * @param g the geometry to buffer
	 */
	BufferOp(const geom::Geometry *g)
		:
		argGeom(g),
		quadrantSegments(OffsetCurveBuilder::DEFAULT_QUADRANT_SEGMENTS),
		endCapStyle(BufferOp::CAP_ROUND),
		resultGeometry(NULL)
	{}

	/**
	 * Specifies the end cap style of the generated buffer.
	 * The styles supported are CAP_ROUND, CAP_BUTT, and CAP_SQUARE.
	 * The default is CAP_ROUND.
	 *
	 * @param endCapStyle the end cap style to specify
	 */
	inline void setEndCapStyle(int nEndCapStyle);

	/**
	 * Specifies the end cap style of the generated buffer.
	 * The styles supported are CAP_ROUND, CAP_BUTT, and CAP_SQUARE.
	 * The default is CAP_ROUND.
	 *
	 * @param endCapStyle the end cap style to specify
	 */
	inline void setQuadrantSegments(int nQuadrantSegments);

	/**
	 * Returns the buffer computed for a geometry for a given buffer
	 * distance.
	 *
	 * @param g the geometry to buffer
	 * @param distance the buffer distance
	 * @return the buffer of the input geometry
	 */
	geom::Geometry* getResultGeometry(double nDistance);

	/**
	 * Comutes the buffer for a geometry for a given buffer distance
	 * and accuracy of approximation.
	 *
	 * @param g the geometry to buffer
	 * @param distance the buffer distance
	 * @param quadrantSegments the number of segments used to
	 * approximate a quarter circle
	 * @return the buffer of the input geometry
	 *
	 * @deprecated use setQuadrantSegments instead
	 */
	geom::Geometry* getResultGeometry(double nDistance, int nQuadrantSegments);
};

// BufferOp inlines
void BufferOp::setQuadrantSegments(int q) { quadrantSegments=q; }
void BufferOp::setEndCapStyle(int s) { endCapStyle=s; }


} // namespace geos::operation::buffer
} // namespace geos::operation
} // namespace geos

#endif // ndef GEOS_OP_BUFFER_BUFFEROP_H

/**********************************************************************
 * $Log$
 * Revision 1.1  2006/03/14 00:19:40  strk
 * opBuffer.h split, streamlined headers in some (not all) files in operation/buffer/
 *
 **********************************************************************/