Method CreateCocoAnchors

dali/operators/ssd/box_encoder_test.cc:974–1024

Creates SSD default boxes (anchors) for COCO dataset. Exact description can be found in https://arxiv.org/abs/1512.02325

  // Creates SSD default boxes (anchors) for COCO dataset.
  // Exact description can be found in https://arxiv.org/abs/1512.02325
  void CreateCocoAnchors() {
    anchors_ = vector<float>(coco_anchors_count_ * 4);

    int fig_size = 300;
    vector<int> feat_sizes {38, 19, 10, 5, 3, 1};
    int feat_count = feat_sizes.size();
    vector<float> steps {8.f, 16.f, 32.f, 64.f, 100.f, 300.f};
    vector<float> scales {21.f, 45.f, 99.f, 153.f, 207.f, 261.f, 315.f};
    vector<vector<int>> aspect_ratios {{2}, {2, 3}, {2, 3}, {2, 3}, {2}, {2}};

    vector<float> fks;
    for (auto &step : steps) fks.push_back(fig_size / step);

    int anchor_idx = 0;
    for (int idx = 0; idx < feat_count; ++idx) {
      auto sk1 = scales[idx] / fig_size;
      auto sk2 = scales[idx + 1] / fig_size;
      auto sk3 = std::sqrt(sk1 * sk2);
      vector<std::pair<float, float>> all_sizes{{sk1, sk1}, {sk3, sk3}};

      for (auto &alpha : aspect_ratios[idx]) {
        auto w = sk1 * sqrt(alpha);
        auto h = sk1 / sqrt(alpha);
        all_sizes.push_back({w, h});
        all_sizes.push_back({h, w});
      }

      for (auto &sizes : all_sizes) {
        auto w = sizes.first;
        auto h = sizes.second;

        for (int i = 0; i < feat_sizes[idx]; ++i)
          for (int j = 0; j < feat_sizes[idx]; ++j) {
            auto cx = (j + 0.5f) / fks[idx];
            auto cy = (i + 0.5f) / fks[idx];

            cx = this->Clamp(cx);
            cy = this->Clamp(cy);
            w = this->Clamp(w);
            h = this->Clamp(h);

            anchors_[anchor_idx * 4] = cx - 0.5f * w;
            anchors_[anchor_idx * 4 + 1] = cy - 0.5f * h;
            anchors_[anchor_idx * 4 + 2] = cx + 0.5f * w;
            anchors_[anchor_idx * 4 + 3] = cy + 0.5f * h;

            ++anchor_idx;
          }
      }
    }
  }

  void CheckAnswersForCoco(TensorList<CPUBackend> *boxes,
                           TensorList<CPUBackend> *labels,