Method ComputeOffsetFeature

deps/tesseract/classify/intfeaturemap.cpp:201–242

Helper to compute an offset index feature. In this context an offset feature with a dir of +/-1 is a feature of a similar direction, but shifted perpendicular to the direction of the feature. An offset feature with a dir of +/-2 is feature at the same position, but rotated by +/- one [compact] quantum. Returns the index of the generated offset feature, or -1 if it doesn't exist. Dir should be in [

// distance moved from the input to guarantee that it maps to the next
// available quantum in the mapped/compact space.
int IntFeatureMap::ComputeOffsetFeature(int index_feature, int dir) const {
  INT_FEATURE_STRUCT f = InverseIndexFeature(index_feature);
  ASSERT_HOST(IndexFeature(f) == index_feature);
  if (dir == 0) {
    return index_feature;
  } else if (dir == 1 || dir == -1) {
    FCOORD feature_dir = FeatureDirection(f.Theta);
    FCOORD rotation90(0.0f, 1.0f);
    feature_dir.rotate(rotation90);
    // Find the nearest existing feature.
    for (int m = 1; m < kMaxOffsetDist; ++m) {
      double x_pos = f.X + feature_dir.x() * (m * dir);
      double y_pos = f.Y + feature_dir.y() * (m * dir);
      int x = IntCastRounded(x_pos);
      int y = IntCastRounded(y_pos);
      if (x >= 0 && x <= MAX_UINT8 && y >= 0 && y <= MAX_UINT8) {
        INT_FEATURE_STRUCT offset_f;
        offset_f.X = x;
        offset_f.Y = y;
        offset_f.Theta = f.Theta;
        int offset_index = IndexFeature(offset_f);
        if (offset_index != index_feature && offset_index >= 0)
          return offset_index;  // Found one.
      } else {
        return -1;  // Hit the edge of feature space.
      }
    }
  } else if (dir == 2 || dir == -2) {
    // Find the nearest existing index_feature.
    for (int m = 1; m < kMaxOffsetDist; ++m) {
      int theta = f.Theta + m * dir / 2;
      INT_FEATURE_STRUCT offset_f;
      offset_f.X = f.X;
      offset_f.Y = f.Y;
      offset_f.Theta = Modulo(theta, 256);
      int offset_index = IndexFeature(offset_f);
      if (offset_index != index_feature && offset_index >= 0)
        return offset_index;  // Found one.
    }
  }
  return -1;  // Nothing within the max distance.
}

}  // namespace tesseract.