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/* Copyright (c) 2008-2025 the MRtrix3 contributors.
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*
* Covered Software is provided under this License on an "as is"
* basis, without warranty of any kind, either expressed, implied, or
* statutory, including, without limitation, warranties that the
* Covered Software is free of defects, merchantable, fit for a
* particular purpose or non-infringing.
* See the Mozilla Public License v. 2.0 for more details.
*
* For more details, see http://www.mrtrix.org/.
*/
#include "axes.h"
namespace MR
{
namespace Axes
{
Shuffle get_shuffle_to_make_RAS(const transform_type &T) {
Shuffle result;
result.permutations = closest(T.linear());
// Figure out whether any of the rows of the transform point in the
// opposite direction to the MRtrix convention
result.flips[result.permutations[0]] = T(0, result.permutations[0]) < 0.0;
result.flips[result.permutations[1]] = T(1, result.permutations[1]) < 0.0;
result.flips[result.permutations[2]] = T(2, result.permutations[2]) < 0.0;
return result;
}
permutations_type closest(const Eigen::Matrix3d &M) {
permutations_type result{-1, -1, -1};
// Find which row of the transform is closest to each scanner axis
Eigen::Matrix3d::Index index(0);
M.row(0).cwiseAbs().maxCoeff(&index);
result[0] = index;
M.row(1).cwiseAbs().maxCoeff(&index);
result[1] = index;
M.row(2).cwiseAbs().maxCoeff(&index);
result[2] = index;
assert(result[0] < 3 && result[1] < 3 && result[2] < 3);
// Disambiguate permutations
auto not_any_of = [] (size_t a, size_t b) -> size_t
{
for (size_t i = 0; i < 3; ++i) {
if (a == i || b == i)
continue;
return i;
}
assert (0);
return std::numeric_limits<size_t>::max();
};
if (result[0] == result[1])
result[1] = not_any_of (result[0], result[2]);
if (result[0] == result[2])
result[2] = not_any_of (result[0], result[1]);
if (result[1] == result[2])
result[2] = not_any_of (result[0], result[1]);
assert (result[0] != result[1] && result[1] != result[2] && result[2] != result[0]);
assert (*std::min_element(result.begin(), result.end()) == 0);
return result;
}
}
}
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