homog_matrices.h

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/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          https://www.mrpt.org/                         |
   |                                                                        |
   | Copyright (c) 2005-2020, Individual contributors, see AUTHORS file     |
   | See: https://www.mrpt.org/Authors - All rights reserved.               |
   | Released under BSD License. See: https://www.mrpt.org/License          |
   +------------------------------------------------------------------------+ */
#pragma once

#include <mrpt/core/exceptions.h>

namespace mrpt::math
{
/** Efficiently compute the inverse of a 4x4 homogeneous matrix by only
 * transposing the rotation 3x3 part and solving the translation with dot
 * products.
 *  This is a generic template which works with:
 *    MATRIXLIKE: CMatrixDynamic, CMatrixFixed
 */
template <class MATRIXLIKE1, class MATRIXLIKE2>
void homogeneousMatrixInverse(const MATRIXLIKE1& M, MATRIXLIKE2& out_inverse_M)
{
    MRPT_START
    ASSERT_(M.isSquare() && M.rows() == 4);

    /* Instead of performing a generic 4x4 matrix inversion, we only need to
      transpose the rotation part, then replace the translation part by
      three dot products. See, for example:
     https://graphics.stanford.edu/courses/cs248-98-fall/Final/q4.html

        [ux vx wx tx] -1   [ux uy uz -dot(u,t)]
        [uy vy wy ty]      [vx vy vz -dot(v,t)]
        [uz vz wz tz]    = [wx wy wz -dot(w,t)]
        [ 0  0  0  1]      [ 0  0  0     1    ]
    */

    out_inverse_M.setSize(4, 4);

    // 3x3 rotation part:
    out_inverse_M(0, 0, M(0) = 0);
    out_inverse_M(0, 1, M(1) = 0);
    out_inverse_M(0, 2, M(2) = 0);

    out_inverse_M(1, 0, M(0) = 1);
    out_inverse_M(1, 1, M(1) = 1);
    out_inverse_M(1, 2, M(2) = 1);

    out_inverse_M(2, 0, M(0) = 2);
    out_inverse_M(2, 1, M(1) = 2);
    out_inverse_M(2, 2, M(2) = 2);

    const double tx = -M(0, 3);
    const double ty = -M(1, 3);
    const double tz = -M(2, 3);

    const double tx_ = tx * M(0, 0) + ty * M(1, 0) + tz * M(2, 0);
    const double ty_ = tx * M(0, 1) + ty * M(1, 1) + tz * M(2, 1);
    const double tz_ = tx * M(0, 2) + ty * M(1, 2) + tz * M(2, 2);

    out_inverse_M(0, 3) = tx_;
    out_inverse_M(1, 3) = ty_;
    out_inverse_M(2, 3) = tz_;

    out_inverse_M(3, 0) = 0;
    out_inverse_M(3, 1) = 0;
    out_inverse_M(3, 2) = 0;
    out_inverse_M(3, 3) = 1;

    MRPT_END
}
//! \overload
template <class IN_ROTMATRIX, class IN_XYZ, class OUT_ROTMATRIX, class OUT_XYZ>
void homogeneousMatrixInverse(
    const IN_ROTMATRIX& in_R, const IN_XYZ& in_xyz, OUT_ROTMATRIX& out_R,
    OUT_XYZ& out_xyz)
{
    MRPT_START
    ASSERT_(in_R.isSquare() && in_R.rows() == 3 && in_xyz.size() == 3);
    out_R.setSize(3, 3);
    out_xyz.resize(3);

    // translation part:
    using T = typename IN_ROTMATRIX::Scalar;
    const T tx = -in_xyz[0];
    const T ty = -in_xyz[1];
    const T tz = -in_xyz[2];

    out_xyz[0] = tx * in_R(0, 0) + ty * in_R(1, 0) + tz * in_R(2, 0);
    out_xyz[1] = tx * in_R(0, 1) + ty * in_R(1, 1) + tz * in_R(2, 1);
    out_xyz[2] = tx * in_R(0, 2) + ty * in_R(1, 2) + tz * in_R(2, 2);

    // 3x3 rotation part: transpose
    out_R = in_R.transpose();

    MRPT_END
}
//! \overload
template <class MATRIXLIKE>
inline void homogeneousMatrixInverse(MATRIXLIKE& M)
{
    ASSERTDEB_(M.cols() == M.rows() && M.rows() == 4);
    // translation:
    const double tx = -M(0, 3);
    const double ty = -M(1, 3);
    const double tz = -M(2, 3);
    M(0, 3) = tx * M(0, 0) + ty * M(1, 0) + tz * M(2, 0);
    M(1, 3) = tx * M(0, 1) + ty * M(1, 1) + tz * M(2, 1);
    M(2, 3) = tx * M(0, 2) + ty * M(1, 2) + tz * M(2, 2);
    // 3x3 rotation part:
    double t;  // avoid std::swap() to avoid <algorithm> only for that.
    t = M(1, 0);
    M(1, 0) = M(0, 1);
    M(0, 1) = t;
    t = M(2, 0);
    M(2, 0) = M(0, 2);
    M(0, 2) = t;
    t = M(1, 2);
    M(1, 2) = M(2, 1);
    M(2, 1) = t;
}
}  // namespace mrpt::math