[sampling] implement point sampler on cylinders

frackit/sampling/CMakeLists.txt

 install(FILES
 boxpointsampler.hh
+cylinderpointsampler.hh
 disksampler.hh
 geometrysampler.hh
 geometrypointsampler.hh

frackit/sampling/cylinderpointsampler.hh

+// -*- mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+// vi: set et ts=4 sw=4 sts=4:
+/*****************************************************************************
+ *   See the file COPYING for full copying permissions.                      *
+ *                                                                           *
+ *   This program is free software: you can redistribute it and/or modify    *
+ *   it under the terms of the GNU General Public License as published by    *
+ *   the Free Software Foundation, either version 2 of the License, or       *
+ *   (at your option) any later version.                                     *
+ *                                                                           *
+ *   This program 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 General Public License for more details.                            *
+ *                                                                           *
+ *   You should have received a copy of the GNU General Public License       *
+ *   along with this program.  If not, see <http://www.gnu.org/licenses/>.   *
+ *****************************************************************************/
+/*!
+ * \file
+ * \brief Class to randomly generate points on cylinders.
+ */
+#ifndef FRACKIT_CYLINDER_POINT_SAMPLER_HH
+#define FRACKIT_CYLINDER_POINT_SAMPLER_HH
+
+#include <cmath>
+#include <random>
+
+#include <frackit/geometry/cylinder.hh>
+#include <frackit/geometry/vector.hh>
+
+#include "pointsampler.hh"
+
+namespace Frackit {
+
+/*!
+ * \brief Class to randomly generate points within cylinders
+ *        following the provided distributions. The type of
+ *        distribution to be used can be specified via traits,
+ *        which are required to exporrt the distributions to be
+ *        used for the squared radius, the angle and the height,
+ *        using the naming convention for three-dimensional geometries,
+ *        i.e. they must export:
+ *        using DistributionBase1 = ...; // Distribution for squared radius
+ *        using DistributionBase2 = ...; // Distribution for the angle
+ *        using DistributionBase3 = ...; // Distribution for the height
+ *
+ * \tparam ctype The type used for coordinates
+ * \tparam T The traits class containing the distributions
+ */
+template<class ctype, class T>
+class CylinderPointSampler
+: public PointSampler< typename Cylinder<ctype>::Point >
+{
+    using DistroRadiusSquared = typename T::DistributionBase1;
+    using DistroAngle = typename T::DistributionBase2;
+    using DistroHeight = typename T::DistributionBase3;
+
+public:
+    //! export resulting point type
+    using Point = typename Cylinder<ctype>::Point;
+
+    //! export traits class
+    using Traits = T;
+
+    /*!
+     * \brief Constructor from a cylinder and distributions.
+     */
+    CylinderPointSampler(const Cylinder<ctype>& cylinder,
+                         const DistroRadiusSquared& pr,
+                         const DistroAngle& pPhi,
+                         const DistroHeight& ph)
+    : bottom_(cylinder.bottomFace())
+    , generator_(std::random_device{}())
+    , p_radiusSquared_(pr)
+    , p_angle_(pPhi)
+    , p_height_(ph)
+    {}
+
+    /*!
+     * \brief Sample a point from the distributions.
+     * \note The distribution for the radius is expected
+     *       to actually be a distribution for the squared
+     *       radius, i.e. it is in the interval [0, r^2].
+     *       After sampling, the square root is taken.
+     */
+    Point operator() () override
+    {
+        const auto phi = p_angle_(generator_);
+        const auto h = p_height_(generator_);
+        auto r = p_radiusSquared_(generator_);
+
+        using std::sqrt;
+        r = sqrt(r);
+
+        using Vector = Frackit::Vector<ctype, 3>;
+        auto a = Vector(bottom_.majorAxis());
+        auto b = Vector(bottom_.minorAxis());
+        auto n = Vector(bottom_.normal());
+
+        using std::sin;
+        using std::cos;
+        a *= r*cos(phi);
+        b *= r*sin(phi);
+        n *= h;
+
+        Point result = bottom_.center();
+        result += a;
+        result += b;
+        result += n;
+
+        return result;
+    }
+
+ private:
+     typename Cylinder<ctype>::Disk bottom_;
+
+     std::default_random_engine generator_;
+     DistroRadiusSquared p_radiusSquared_;
+     DistroAngle  p_angle_;
+     DistroHeight p_height_;
+};
+
+} // end namespace Frackit
+
+#endif // FRACKIT_CYLINDER_POINT_SAMPLER_HH