mirror of https://github.com/CGAL/cgal
92 lines
2.6 KiB
C++
92 lines
2.6 KiB
C++
// Copyright (c) 2022 INRIA Sophia-Antipolis (France).
|
|
// All rights reserved.
|
|
//
|
|
// This file is part of CGAL (www.cgal.org).
|
|
//
|
|
// $URL$
|
|
// $Id$
|
|
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-Commercial
|
|
//
|
|
// Author(s) : Julian Stahl
|
|
|
|
#ifndef CGAL_FINITE_DIFFERENCE_GRADIENT_H
|
|
#define CGAL_FINITE_DIFFERENCE_GRADIENT_H
|
|
|
|
#include <CGAL/license/Isosurfacing_3.h>
|
|
|
|
namespace CGAL {
|
|
namespace Isosurfacing {
|
|
|
|
/**
|
|
* \ingroup PkgIsosurfacing3Ref
|
|
*
|
|
* \brief Class template for a gradient that is calculated using finite differences.
|
|
*
|
|
* \details This gradient function evaluates an implicit value function at six points
|
|
* that are a given distance `delta` away from the queried point.
|
|
*
|
|
* \tparam GeomTraits the traits for this gradient.
|
|
*
|
|
* \tparam PointFunction the type of the implicit function. It must implement `GeomTraits::FT operator()(const
|
|
* GeomTraits::Point& point) const`.
|
|
*/
|
|
template <typename GeomTraits,
|
|
typename PointFunction>
|
|
class Finite_difference_gradient
|
|
{
|
|
public:
|
|
using Geom_traits = GeomTraits;
|
|
using FT = typename Geom_traits::FT;
|
|
using Point = typename Geom_traits::Point_3;
|
|
using Vector = typename Geom_traits::Vector_3;
|
|
|
|
public:
|
|
/**
|
|
* \ingroup PkgIsosurfacing3Ref
|
|
*
|
|
* \brief Create a new instance of this gradient.
|
|
*
|
|
* \param point_function the function with a point as argument
|
|
* \param delta the distance for calculating the finite differences
|
|
*/
|
|
Finite_difference_gradient(const PointFunction& point_function,
|
|
const FT delta = 0.001)
|
|
: func(point_function),
|
|
delta(delta)
|
|
{ }
|
|
|
|
/**
|
|
* \ingroup PkgIsosurfacing3Ref
|
|
*
|
|
* \brief Evaluate the gradient at a point in space.
|
|
*
|
|
* \param point the point at which the gradient is computed
|
|
*/
|
|
Vector operator()(const Point& point) const
|
|
{
|
|
// compute the gradient by sampling the function with finite differences
|
|
// at six points with distance delta around the query point
|
|
const Point p0 = point + Vector(delta, 0, 0);
|
|
const Point p1 = point - Vector(delta, 0, 0);
|
|
const Point p2 = point + Vector(0, delta, 0);
|
|
const Point p3 = point - Vector(0, delta, 0);
|
|
const Point p4 = point + Vector(0, 0, delta);
|
|
const Point p5 = point - Vector(0, 0, delta);
|
|
|
|
const FT gx = (func(p0) - func(p1)) / (2 * delta);
|
|
const FT gy = (func(p2) - func(p3)) / (2 * delta);
|
|
const FT gz = (func(p4) - func(p5)) / (2 * delta);
|
|
|
|
return Vector(gx, gy, gz);
|
|
}
|
|
|
|
private:
|
|
const PointFunction func;
|
|
FT delta;
|
|
};
|
|
|
|
} // namespace Isosurfacing
|
|
} // namespace CGAL
|
|
|
|
#endif // CGAL_FINITE_DIFFERENCE_GRADIENT_H
|