projection.h

/*****************************************************************************
 * VCLib                                                                     *
 * Visual Computing Library                                                  *
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 * Copyright(C) 2021-2025                                                    *
 * Visual Computing Lab                                                      *
 * ISTI - Italian National Research Council                                  *
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#ifndef VCL_ALGORITHMS_CORE_POLYGON_PROJECTION_H
#define VCL_ALGORITHMS_CORE_POLYGON_PROJECTION_H
 
#include <vclib/concepts/space/point.h>
#include <vclib/space/core/polygon.h>
 
namespace vcl {
 
template<Point3IteratorConcept Iterator>
auto project(Iterator begin, Iterator end)
{
    using PointType  = Iterator::value_type;
    using ScalarType = PointType::ScalarType;
 
    Polygon2<ScalarType> projectedPolygon;
 
    // Calculate the normal vector of the polygon and an orthonormal basis
    // for the plane containing the polygon.
    PointType normal = Polygon3<ScalarType>::normal(begin, end);
    PointType u, v;
    normal.orthoBase(u, v);
 
    projectedPolygon.reserve(std::distance(begin, end));
 
    // Project each vertex onto the plane defined by the orthonormal basis.
    for (auto it = begin; it != end; ++it) {
        ScalarType x = (*it).dot(u);
        ScalarType y = (*it).dot(v);
        projectedPolygon.pushBack(Point2<ScalarType>(x, y));
    }
 
    return projectedPolygon;
}
 
template<Range R>
auto project(R&& polygon) requires Point3Concept<std::ranges::range_value_t<R>>
{
    return project(polygon.begin(), polygon.end());
}
 
} // namespace vcl
 
#endif // VCL_ALGORITHMS_CORE_POLYGON_PROJECTION_H