Utility.h

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#pragma once

#include "open3d/core/Tensor.h"

namespace open3d {
namespace t {
namespace geometry {

inline core::Tensor InverseTransformation(const core::Tensor& T) {
    T.AssertShape({4, 4});
    T.AssertDtype(core::Dtype::Float64);
    T.AssertDevice(core::Device("CPU:0"));
    if (!T.IsContiguous()) {
        utility::LogError("T is expected to be contiguous");
    }

    core::Tensor Tinv({4, 4}, core::Dtype::Float64, core::Device("CPU:0"));
    const double* T_ptr = T.GetDataPtr<double>();
    double* Tinv_ptr = Tinv.GetDataPtr<double>();

    // R' = R.T
    Tinv_ptr[0 * 4 + 0] = T_ptr[0 * 4 + 0];
    Tinv_ptr[0 * 4 + 1] = T_ptr[1 * 4 + 0];
    Tinv_ptr[0 * 4 + 2] = T_ptr[2 * 4 + 0];

    Tinv_ptr[1 * 4 + 0] = T_ptr[0 * 4 + 1];
    Tinv_ptr[1 * 4 + 1] = T_ptr[1 * 4 + 1];
    Tinv_ptr[1 * 4 + 2] = T_ptr[2 * 4 + 1];

    Tinv_ptr[2 * 4 + 0] = T_ptr[0 * 4 + 2];
    Tinv_ptr[2 * 4 + 1] = T_ptr[1 * 4 + 2];
    Tinv_ptr[2 * 4 + 2] = T_ptr[2 * 4 + 2];

    // t' = -R.T @ t = -R' @ t
    Tinv_ptr[0 * 4 + 3] = -(Tinv_ptr[0 * 4 + 0] * T_ptr[0 * 4 + 3] +
                            Tinv_ptr[0 * 4 + 1] * T_ptr[1 * 4 + 3] +
                            Tinv_ptr[0 * 4 + 2] * T_ptr[2 * 4 + 3]);
    Tinv_ptr[1 * 4 + 3] = -(Tinv_ptr[1 * 4 + 0] * T_ptr[0 * 4 + 3] +
                            Tinv_ptr[1 * 4 + 1] * T_ptr[1 * 4 + 3] +
                            Tinv_ptr[1 * 4 + 2] * T_ptr[2 * 4 + 3]);
    Tinv_ptr[2 * 4 + 3] = -(Tinv_ptr[2 * 4 + 0] * T_ptr[0 * 4 + 3] +
                            Tinv_ptr[2 * 4 + 1] * T_ptr[1 * 4 + 3] +
                            Tinv_ptr[2 * 4 + 2] * T_ptr[2 * 4 + 3]);

    // Remaining part
    Tinv_ptr[3 * 4 + 0] = 0;
    Tinv_ptr[3 * 4 + 1] = 0;
    Tinv_ptr[3 * 4 + 2] = 0;
    Tinv_ptr[3 * 4 + 3] = 1;

    return Tinv;
}
}  // namespace geometry
}  // namespace t
}  // namespace open3d