Manifold.h

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/* ----------------------------------------------------------------------------

 * GTSAM Copyright 2010, Georgia Tech Research Corporation,
 * Atlanta, Georgia 30332-0415
 * All Rights Reserved
 * Authors: Frank Dellaert, et al. (see THANKS for the full author list)

 * See LICENSE for the license information

 * -------------------------------------------------------------------------- */

#pragma once

#include <gtsam/base/Matrix.h>
#include <gtsam/base/Testable.h>
#include <gtsam/base/OptionalJacobian.h>
#include <gtsam/base/concepts.h>

namespace gtsam {

struct manifold_tag {};

template <typename T> struct traits;

namespace internal {

template<class Class>
struct HasManifoldPrereqs {

  enum { dim = Class::dimension };

  Class p, q;
  Eigen::Matrix<double, dim, 1> v;
  OptionalJacobian<dim, dim> Hp, Hq, Hv;

  BOOST_CONCEPT_USAGE(HasManifoldPrereqs) {
    v = p.localCoordinates(q);
    q = p.retract(v);
  }
};

template<class Class, int N>
struct GetDimensionImpl {
  // Compile-time dimensionality
  static int GetDimension(const Class&) {
    return N;
  }
};

template<class Class>
struct GetDimensionImpl<Class, Eigen::Dynamic> {
  // Run-time dimensionality
  static int GetDimension(const Class& m) {
    return m.dim();
  }
};

template<class Class>
struct ManifoldTraits: GetDimensionImpl<Class, Class::dimension> {

  // Check that Class has the necessary machinery
  GTSAM_CONCEPT_ASSERT(HasManifoldPrereqs<Class>);

  // Dimension of the manifold
  enum { dimension = Class::dimension };

  // Typedefs required by all manifold types.
  typedef Class ManifoldType;
  typedef manifold_tag structure_category;
  typedef Eigen::Matrix<double, dimension, 1> TangentVector;

  // Local coordinates
  static TangentVector Local(const Class& origin, const Class& other) {
    return origin.localCoordinates(other);
  }

  // Retraction back to manifold
  static Class Retract(const Class& origin, const TangentVector& v) {
    return origin.retract(v);
  }
};

template<class Class> struct Manifold: ManifoldTraits<Class>, Testable<Class> {};

} // \ namespace internal

template<typename T>
GTSAM_CONCEPT_REQUIRES(IsTestable<T>, bool) //
check_manifold_invariants(const T& a, const T& b, double tol=1e-9) {
  typename traits<T>::TangentVector v0 = traits<T>::Local(a,a);
  typename traits<T>::TangentVector v = traits<T>::Local(a,b);
  T c = traits<T>::Retract(a,v);
  return v0.norm() < tol && traits<T>::Equals(b,c,tol);
}

template<typename T>
class IsManifold {

public:

  typedef typename traits<T>::structure_category structure_category_tag;
  static const int dim = traits<T>::dimension;
  typedef typename traits<T>::ManifoldType ManifoldType;
  typedef typename traits<T>::TangentVector TangentVector;

  BOOST_CONCEPT_USAGE(IsManifold) {
    static_assert(
        (std::is_base_of<manifold_tag, structure_category_tag>::value),
        "This type's structure_category trait does not assert it as a manifold (or derived)");
    static_assert(TangentVector::SizeAtCompileTime == dim);

    // make sure Chart methods are defined
    v = traits<T>::Local(p, q);
    q = traits<T>::Retract(p, v);
  }

private:

  TangentVector v;
  ManifoldType p, q;
};

template<typename T>
struct FixedDimension {
  typedef const int value_type;
  static const int value = traits<T>::dimension;
  static_assert(value != Eigen::Dynamic,
      "FixedDimension instantiated for dymanically-sized type.");
};
} // \ namespace gtsam

// * Macros for using the ManifoldConcept
// *  - An instantiation for use inside unit tests
// *  - A typedef for use inside generic algorithms
// *
// * NOTE: intentionally not in the gtsam namespace to allow for classes not in
// * the gtsam namespace to be more easily enforced as testable
// */
#define GTSAM_CONCEPT_MANIFOLD_INST(T) template class gtsam::IsManifold<T>;
#define GTSAM_CONCEPT_MANIFOLD_TYPE(T) using _gtsam_IsManifold_##T = gtsam::IsManifold<T>;