Package org.orekit.frames

Class UpdatableFrame

  • All Implemented Interfaces:
    Serializable
    public class UpdatableFrame
extends Frame
    Frame whose transform from its parent can be updated.

    This class allows to control the relative position of two parts of the global frames tree using any two frames in each part as control handles. Consider the following simplified frames tree as an example:

                  GCRF
                |
  --------------------------------
  |             |                |
 Sun        satellite          Earth
                |                |
        on-board antenna   ground station
                                 |
                          tracking antenna

    Tracking measurements really correspond to the link between the ground and on-board antennas. This is tightly linked to the transform between these two frames, however neither frame is the direct parent frame of the other one: the path involves four intermediate frames. When we process a measurement, what we really want to update is the transform that defines the satellite frame with respect to its parent GCRF frame.

    In order to implement the above case, the satellite frame is defined as an instance of this class and its updateTransform would be called each time we want to adjust the frame, i.e. each time we get a new measurement between the two antennas.

    Author:
    Luc Maisonobe
    See Also:
    Serialized Form

    • Constructor Detail

      • UpdatableFrame

        public UpdatableFrame​(Frame parent,
                      Transform transform,
                      String name,
                      boolean pseudoInertial)
               throws IllegalArgumentException
        Build a frame from its transform with respect to its parent.

        The convention for the transform is that it is from parent frame to instance. This means that the two following frames are similar:

         Frame frame1 = new Frame(FramesFactory.getGCRF(), new Transform(t1, t2));
 Frame frame2 = new Frame(new Frame(FramesFactory.getGCRF(), t1), t2);
        Parameters:
        parent - parent frame (must be non-null)
        transform - transform from parent frame to instance
        name - name of the frame
        pseudoInertial - true if frame is considered pseudo-inertial (i.e. suitable for propagating orbit)
        Throws:
        IllegalArgumentException - if the parent frame is null

    • Method Detail

      • updateTransform

        public void updateTransform​(Frame f1,
                            Frame f2,
                            Transform f1Tof2,
                            AbsoluteDate date)
        Update the transform from parent frame implicitly according to two other frames.

        This method allows to control the relative position of two parts of the global frames tree using any two frames in each part as control handles. Consider the following simplified frames tree as an example:

                      GCRF
                |
  --------------------------------
  |             |                |
 Sun        satellite          Earth
                |                |
        on-board antenna   ground station
                                 |
                          tracking antenna

        Tracking measurements really correspond to the link between the ground and on-board antennas. This is tightly linked to the transform between these two frames, however neither frame is the direct parent frame of the other one: the path involves four intermediate frames. When we process a measurement, what we really want to update is the transform that defines the satellite frame with respect to its parent GCRF frame. This is the purpose of this method. This update is done by the following call, where measurementTransform represents the measurement as a simple translation transform between the two antenna frames:

        
 satellite.updateTransform(onBoardAntenna, trackingAntenna,
                           measurementTransform, date);

        One way to represent the behavior of the method is to consider the sub-tree rooted at the instance on one hand (satellite and on-board antenna in the example above) and the tree containing all the other frames on the other hand (GCRF, Sun, Earth, ground station, tracking antenna). Both tree are considered as two solid sets linked together by a flexible spring, which is the transform we want to update. The method stretches the spring to make sure the transform between the two specified frames (one in each tree part) matches the specified transform.

        Parameters:
        f1 - first control frame (may be the instance itself)
        f2 - second control frame (may be the instance itself)
        f1Tof2 - desired transform from first to second control frame
        date - date of the transform