DGtal  0.9.3beta
geometry/tools/exampleAlphaShape.cpp

Computation of the alpha shape of the border of a digital shape.

See also
Convex hull and alpha-shape in the plane
#include <iostream>
#include "DGtal/base/Common.h"
#include "DGtal/base/IteratorCirculatorTraits.h"
#include "DGtal/helpers/StdDefs.h"
#include "DGtal/geometry/tools/Hull2DHelpers.h"
#include "DGtal/geometry/tools/PolarPointComparatorBy2x2DetComputer.h"
#include "DGtal/geometry/tools/determinant/AvnaimEtAl2x2DetSignComputer.h"
#include "DGtal/geometry/tools/determinant/InHalfPlaneBySimple3x3Matrix.h"
#include "DGtal/geometry/tools/determinant/InGeneralizedDiskOfGivenRadius.h"
#include "DGtal/shapes/ShapeFactory.h"
#include "DGtal/shapes/Shapes.h"
#include "DGtal/topology/DigitalSetBoundary.h"
#include "DGtal/topology/DigitalSurface.h"
#include "DGtal/graph/DepthFirstVisitor.h"
#include "DGtal/io/boards/Board2D.h"
using namespace std;
using namespace DGtal;
/*
* @brief Procedure that draws on a board a polygon given by a range of vertices.
* @param itb begin iterator
* @param ite end iterator
* @param aBoard any board
* @param isClosed bool equal to 'true' for closed polygon, 'false' otherwise.
* @tparam ForwardIterator at least a readable and forward iterator
* @tparam Board equivalent to Board2D
*/
template <typename ForwardIterator, typename Board>
void drawPolygon(const ForwardIterator& itb, const ForwardIterator& ite,
Board& aBoard, bool isClosed = true)
{
ForwardIterator it = itb;
if (it != ite)
{//for the first point
Point p1 = *it;
Point p = p1;
//display
aBoard << SetMode( p.className(), "Grid" )
<< CustomStyle( p.className()+"/Grid", new CustomPenColor( Color::Red ) )
<< p
<< CustomStyle( p.className()+"/Grid", new CustomPenColor( Color::Black ) );
Point prev = p;
for (++it; it != ite; ++it, prev = p)
{//for all other points
//conversion
p = *it;
//display
aBoard << p;
if (prev != p)
aBoard.drawArrow(prev[0], prev[1], p[0], p[1]);
}
//display the last edge too
if (isClosed)
{
if (prev != p1)
aBoard.drawArrow(prev[0], prev[1], p1[0], p1[1]);
}
}
}
void alphaShape()
{
//Digitization of a disk of radius 8
Z2i::Domain domain(ball.getLowerBound(), ball.getUpperBound());
Z2i::DigitalSet digitalSet(domain);
//Contour of the digital set
Z2i::KSpace kspace;
kspace.init(domain.lowerBound()-Z2i::Point(1,1), domain.upperBound()+Z2i::Point(1,1), true);
typedef DigitalSetBoundary<Z2i::KSpace, Z2i::DigitalSet> DigitalSurfaceContainer;
typedef DigitalSurface<DigitalSurfaceContainer> CustomDigitalSurface;
DigitalSurfaceContainer digitalSurfaceContainer( kspace, digitalSet );
CustomDigitalSurface digitalSurface( digitalSurfaceContainer );
//Grid curve
Z2i::Curve gridCurve;
CustomVisitor visitor( digitalSurface, *digitalSurface.begin() );
while ( ! visitor.finished() )
{
gridCurve.pushBack( visitor.current().first );
visitor.expand();
}
//Point set defined as the set of (not duplicated) inner points
typedef Z2i::Curve::InnerPointsRange PointRange;
PointRange pointsRange = gridCurve.getInnerPointsRange();
vector<Z2i::Point> border;
unique_copy( pointsRange.begin(), pointsRange.end(), back_inserter( border ) );
//namespace for hull functions
using namespace functions::Hull2D;
{ //alpha = 0
trace.info() << " alpha == 0 " << endl;
vector<Z2i::Point> res;
Functor functor(true, 1, 0); //alpha = 0; 1/alpha -> +inf
Predicate predicate( functor );
closedGrahamScanFromAnyPoint( border.begin(), border.end(), back_inserter( res ), predicate );
//display
Board2D board;
drawPolygon( res.begin(), res.end(), board );
board.saveSVG( "AlphaShape0.svg" );
#ifdef WITH_CAIRO
board.saveCairo("AlphaShape0.png", Board2D::CairoPNG);
#endif
}
{ //alpha = 0
trace.info() << " alpha == 0 " << endl;
vector<Z2i::Point> res;
//comparator and functor
Functor functor;
Predicate predicate( functor );
closedGrahamScanFromAnyPoint( border.begin(), border.end(), back_inserter( res ), predicate );
//display
Board2D board;
drawPolygon( res.begin(), res.end(), board );
board.saveSVG( "AlphaShape0bis.svg" );
#ifdef WITH_CAIRO
board.saveCairo("AlphaShape0bis.png", Board2D::CairoPNG);
#endif
}
//negative alpha shape
{ //alpha = -1
trace.info() << " alpha == -1 " << endl;
vector<Z2i::Point> res;
Functor functor(false, 1, 1); //1/alpha = -sqrt(1/1) = -1
Predicate predicate( functor );
closedGrahamScanFromAnyPoint( border.begin(), border.end(), back_inserter( res ), predicate );
//display
Board2D board;
drawPolygon( res.begin(), res.end(), board );
board.saveSVG( "AlphaShapeM1.svg" );
#ifdef WITH_CAIRO
board.saveCairo("AlphaShapeM1.png", Board2D::CairoPNG);
#endif
}
{ //alpha = -sqrt(5)
trace.info() << " alpha == -sqrt(5) " << endl;
vector<Z2i::Point> res;
Functor functor(false, 5, 1); //1/alpha = -sqrt(5)
Predicate predicate( functor );
closedGrahamScanFromAnyPoint( border.begin(), border.end(), back_inserter( res ), predicate );
//display
Board2D board;
drawPolygon( res.begin(), res.end(), board );
board.saveSVG( "AlphaShapeMSqrt5.svg" );
#ifdef WITH_CAIRO
board.saveCairo("AlphaShapeMSqrt5.png", Board2D::CairoPNG);
#endif
}
{ //alpha = -5
trace.info() << " alpha == -5 " << endl;
vector<Z2i::Point> res;
Functor functor(false, 25, 1); //1/alpha = -sqrt(25/1) = -5
Predicate predicate( functor );
closedGrahamScanFromAnyPoint( border.begin(), border.end(), back_inserter( res ), predicate );
//display
Board2D board;
drawPolygon( res.begin(), res.end(), board );
board.saveSVG( "AlphaShapeM5.svg" );
#ifdef WITH_CAIRO
board.saveCairo("AlphaShapeM5.png", Board2D::CairoPNG);
#endif
}
//positive alpha shape
{
trace.info() << " alpha == 8 " << endl;
vector<Z2i::Point> res;
Functor functor(true, 64, 1); //1/alpha = sqrt(64/1) = 8
Predicate predicate( functor );
closedGrahamScanFromAnyPoint( border.begin(), border.end(), back_inserter( res ), predicate );
//display
Board2D board;
drawPolygon( res.begin(), res.end(), board );
board.saveSVG( "AlphaShapeP8.svg" );
#ifdef WITH_CAIRO
board.saveCairo("AlphaShapeP8.png", Board2D::CairoPNG);
#endif
}
//positive alpha shape
{
trace.info() << " alpha == 9 " << endl;
vector<Z2i::Point> res;
Functor functor(true, 81, 1); //1/alpha = sqrt(81/1) = 9
Predicate predicate( functor );
closedGrahamScanFromAnyPoint( border.begin(), border.end(), back_inserter( res ), predicate );
//display
Board2D board;
drawPolygon( res.begin(), res.end(), board );
board.saveSVG( "AlphaShapeP9.svg" );
#ifdef WITH_CAIRO
board.saveCairo("AlphaShapeP9.png", Board2D::CairoPNG);
#endif
}
}
int main( int argc, char** argv )
{
trace.beginBlock ( "Example exampleAlphaShape" );
trace.info() << "Args:";
for ( int i = 0; i < argc; ++i )
trace.info() << " " << argv[ i ];
trace.info() << endl;
alphaShape();
return 0;
}
// //