orb_angle

/*
Copyright (C) 2018-2024 Geoffrey Daniels. https://gpdaniels.com/

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, version 3 of the License only.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

#pragma once
#ifndef GTL_VISION_FEATURE_ANGLE_ORB_ANGLE_HPP
#define GTL_VISION_FEATURE_ANGLE_ORB_ANGLE_HPP

// Summary: Implemetation of feature angle from the paper "ORB: An efficient alternative to SIFT or SURF". IEEE International Conference on Computer Vision (2011). [wip]

#if defined(_MSC_VER)
    #pragma warning(push, 0)
#endif

#include <cmath>

#if defined(_MSC_VER)
    #pragma warning(pop)
#endif

namespace gtl {
    float orb_angle(
        const unsigned char* __restrict const data,
        const int stride
    );
    float orb_angle(
        const unsigned char* __restrict const data,
        const int stride
    ) {
        // This is the standard set of pattern sample locations for a patch size of 31.
        constexpr static const int patch_size = 31;
        constexpr static const int patch_radius = patch_size / 2;
        constexpr static const int patch_width[patch_radius + 1] = { 15, 15, 15, 15, 14, 14, 14, 13, 13, 12, 11, 10, 9, 8, 6, 3 };


        // Sum the pixel weighted centre row.
        int sum_x = 0;
        for (int x = -patch_radius; x <= patch_radius; ++x) {
            sum_x += x * data[x];
        }

        // Sum the remaining pixel weighted rows in pairs above and below.
        int sum_y = 0;
        for (int y = 1; y <= patch_radius; ++y) {
            int sum = 0;
            for (int x = -patch_width[y]; x <= patch_width[y]; ++x) {
                const int above = data[x - y * stride];
                const int below = data[x + y * stride];
                sum += (below - above);
                sum_x += x * (below + above);
            }
            sum_y += y * sum;
        }

        return std::atan2(static_cast<float>(sum_y), static_cast<float>(sum_x));
    }
}

#endif // GTL_VISION_FEATURE_ANGLE_ORB_ANGLE_HPP