113 lines
3.2 KiB
C
113 lines
3.2 KiB
C
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/**********************************************************************
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*
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* GEOS - Geometry Engine Open Source
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* http://geos.osgeo.org
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*
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* Copyright (C) 2020 Paul Ramsey <pramsey@cleverelephant.ca>
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*
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* This is free software; you can redistribute and/or modify it under
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* the terms of the GNU Lesser General Public Licence as published
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* by the Free Software Foundation.
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* See the COPYING file for more information.
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*
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**********************************************************************/
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#pragma once
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#include <geos/export.h>
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#include <geos/geom/Envelope.h>
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#include <geos/geom/CoordinateSequence.h>
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// Forward declarations
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namespace geos {
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namespace geom {
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class Coordinate;
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class CoordinateSequence;
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}
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}
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using namespace geos::geom;
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namespace geos { // geos.
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namespace operation { // geos.operation
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namespace overlayng { // geos.operation.overlayng
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/**
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* Clips rings of points to a rectangle.
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* Uses a variant of Cohen-Sutherland clipping.
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*
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* In general the output is not topologically valid.
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* In particular, the output may contain coincident non-noded line segments
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* along the clip rectangle sides.
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* However, the output is sufficiently well-structured
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* that it can be used as input to the {@link OverlayNG} algorithm
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* (which is able to process coincident linework due
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* to the need to handle topology collapse under precision reduction).
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*
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* Because of the likelihood of creating
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* extraneous line segments along the clipping rectangle sides,
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* this class is not suitable for clipping linestrings.
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*
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* The clipping envelope should be generated using {@link RobustClipEnvelopeComputer},
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* to ensure that intersecting line segments are not perturbed
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* by clipping.
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* This is required to ensure that the overlay of the
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* clipped geometry is robust and correct (i.e. the same as
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* if clipping was not used).
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*
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* @see LineLimiter
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*
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* @author Martin Davis
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*
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*/
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class GEOS_DLL RingClipper {
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private:
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// Constants
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static constexpr int BOX_LEFT = 3;
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static constexpr int BOX_TOP = 2;
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static constexpr int BOX_RIGHT = 1;
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static constexpr int BOX_BOTTOM = 0;
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// Members
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const Envelope clipEnv;
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// Methods
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/**
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* Clips line to the axis-parallel line defined by a single box edge.
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*/
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std::unique_ptr<CoordinateSequence> clipToBoxEdge(const CoordinateSequence* pts, int edgeIndex, bool closeRing) const;
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/**
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* Computes the intersection point of a segment
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* with an edge of the clip box.
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* The segment must be known to intersect the edge.
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*/
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void intersection(const Coordinate& a, const Coordinate& b, int edgeIndex, Coordinate& rsltPt) const;
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double intersectionLineY(const Coordinate& a, const Coordinate& b, double y) const;
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double intersectionLineX(const Coordinate& a, const Coordinate& b, double x) const;
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bool isInsideEdge(const Coordinate& p, int edgeIndex) const;
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public:
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RingClipper(const Envelope* env)
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: clipEnv(*env)
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{};
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/**
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* Clips a list of points to the clipping rectangle box.
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*/
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std::unique_ptr<CoordinateSequence> clip(const CoordinateSequence* cs) const;
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};
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} // namespace geos.operation.overlayng
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} // namespace geos.operation
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} // namespace geos
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