y2020/vision/sift/sift.fbs

namespace frc971.vision.sift;

// Represents a single feature extracted from an image.
table Feature {
  // Contains the descriptor data.
  //
  // TODO(Brian): These are scaled to be convertible to chars. Should we do
  // that to minimize storage space? Or maybe int16?
  //
  // The size of this depends on the parameters. It is width*width*hist_bins.
  // Currently we have width=4 and hist_bins=8, which results in a size of
  // 4*4*8=128.
  descriptor:[float];

  // Location of the keypoint.
  x:float;
  y:float;

  // Size of the keypoint neighborhood.
  size:float;

  // Angle of the keypoint.
  // This is in [0,360) clockwise.
  angle:float;

  // How good of a keypoint this is.
  response:float;

  // Which octave this keypoint is from.
  octave:int;
}

// Represents a single match between a training image and a query image.
table Match {
  // The index of the feature for the query image.
  query_feature:int;
  // The index of the feature for the training image.
  train_feature:int;
}

// Represents all the matches between a single training image and a query
// image.
table ImageMatch {
  matches:[Match];
  // The index of the training image within all the training images.
  train_image:int;
}

table TransformationMatrix {
  // The matrix data. This is a row-major 3x4 matrix.
  data:[double];
}

// Contains the information the EKF wants from an image.
//
// This is represented as a transformation to a target in field coordinates.
table CameraPose {
  // Transformation matrix from the target to the camera's origin.
  camera_to_target:TransformationMatrix;

  // Field coordinates of the target, represented as a transformation matrix
  // from the target to the field.
  // (0, 0, 0) is the center of the field, on the level of most of the field
  // (not the region under the truss). Positive X is towards the red alliance's
  // PLAYER STATION. Positive Z is up. The coordinate system is right-handed.
  //
  // Note that the red PLAYER STATION is where the red drive teams are. This is
  // often where the blue robots are shooting towards.
  //
  // The value here will be selected from a small, static set of targets we
  // train images on.
  field_to_target:TransformationMatrix;
}

table ImageMatchResult {
  // The matches from this image to each of the training images which matched.
  image_matches:[ImageMatch];
  // The transformations for this image for each of the training images which
  // matched.
  // TODO(Brian): Include some kind of covariance information for these.
  camera_poses:[CameraPose];

  // The features for this image.
  features:[Feature];

  // Timestamp when the frame was captured.
  image_monotonic_timestamp_ns:long;
}

root_type ImageMatchResult;