Camera Ground Projection and Protection Using Orekit/Rugged

1

Hello Orekit/Rugged Team,

I am working on a project that involves satellite imaging, and I need assistance with Java implementation using Orekit or Rugged. Specifically, I have the following questions:

  1. Camera Side Protection on the Ground
  • Given the roll, yaw, and pitch angles of a satellite-mounted camera, how can I compute the ground footprint or the side protection region on the Earth’s surface?
  • Are there any existing utilities in Orekit or Rugged that can help with this computation?
  1. Camera Projection Simulation on the Ground
  • How can I simulate the camera projection on the ground and obtain the coordinates of the projected field of view (protection cone)?
  • Does Rugged provide a way to compute the bounding coordinates of the camera’s footprint given its orientation and position?

Any guidance, example code, or references to relevant classes/methods would be greatly appreciated!

Thank you in advance for your support.

2

Hi @MohamedEmbaby85

Given the rotation angles, you will have to set up an attitude law (most probably a LofOffset).
You will also need an implementation of FieldOfView, for example DoubleDihedraFieldOfView which is a special case of PolygonalFieldOfView or CircularFieldOfView to define the shape of the field of view in spacecraft frame. This field of view has a getFootprint which you can call at any time to evaluate the footprint. The computation of the first argument, Tranform fovToBody is done by combining the transform from inertial frame to central body and the inverse of the transform from inertial frame to field of view as follows, assuming state is the current SpacecraftState:

Transform inertToBody = state.getFrame().getTransformTo(earth.getBodyFrame(),
                                                        state.getDate());
Tranform fovToBody = new Transform(state.getDate(),
                                   state.toTransform().getInverse(),
                                   inertToBody);

Projecting one single line of sight that would correspond to the corners of the field of view can be done using the same method PolygonalFieldOfView uses in its internal loops when it implements getFootprint:

 Vector3D awaySC      = new Vector3D(1.0e6, direction);
 Vector3D awayBody    = fovToBody.transformPosition(awaySC);
 Line     lineOfSight = new Line(position, awayBody, 1.0e-3);
 GeodeticPoint  gp    = body.getIntersectionPoint(lineOfSight, position,
                                                  bodyFrame, null);

Here, 1.0e6 is just an arbitrary distance (1000km) away from the satellite in the specified direction. Beware the gp may be null if the direction misses Earth surface.

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