WebGeocalc (WGC) provides a web-based graphical user interface for many observation geometry calculations available in the “SPICE” system. WGC users can perform SPICE calculations without writing any programs.

Main Features:

• Geometry Calculator
  • State Vector: Calculates the position and velocity of a target relative to an observer
  • Angular Separation: Calculates the angular difference between two directions
  • Angular Size: Calculates the angular size of a target as seen from the observer
  • Frame Transformation: Calculates the transformation from one reference frame (Frame 1) to another reference frame (Frame 2)
  • Illumination Angles: Calculates the emission angle, incidence angle, and phase angle at a point on the target as seen from the observer
  • Phase Angle: Calculates the phase angle defined by the centers of the illumination source, target, and observer
  • Pointing Direction: Calculates the pointing direction in a user-specified reference frame and outputs it as a unit vector or a full-magnitude vector expressed in a user-specified coordinate system
  • Sub-Solar Point: Calculates the sub-solar point on the target as seen from the observer
  • Sub-Observer Point: Calculates the sub-observer point on the target as seen from the observer
  • Surface Intercept Point: Calculates the intercept point of a vector on the target as seen from the observer
  • Tangent Point: Calculates the tangent point between a specified observer, a ray emitted from the observer, and the target
  • Orbital Elements: Calculates the osculating elements of the target’s orbit around the central body (the orbit may be elliptical, parabolic, or hyperbolic)
• Geometric Event Finder
  • Position Event Finder: Finds time intervals when the coordinates of the observer-target position vector satisfy specified conditions
  • Angular Separation Event Finder: Finds time intervals when the angle between two objects as seen from the observer satisfies specified conditions
  • Distance Event Finder: Finds time intervals when the distance between the target and observer satisfies specified conditions
  • Sub-Point Event Finder: Finds time intervals when the coordinates of the sub-observer point on the target satisfy specified conditions
  • Occultation Event Finder: Finds time intervals when the observer sees one target occulted by or transiting another target
  • Surface Intercept Event Finder: Finds time intervals when the coordinates of the surface intercept vector satisfy specified conditions
  • Target in Field of View Event Finder: Finds time intervals when the target intersects the space defined by the instrument’s field of view
  • Ray in Field of View Event Finder: Finds time intervals when a specified ray is contained within the space enclosed by the instrument’s field of view
  • Range Rate Event Finder: Finds time intervals when the range rate between the target and observer satisfies specified conditions
  • Phase Angle Event Finder: Finds time intervals when the specified constraints on the phase angle defined by the centers of the illumination source, target, and observer are satisfied
  • Illumination Angles Event Finder: Finds time intervals when the observed illumination angles at a surface point satisfy specified conditions
• Time Calculator
  • Time Conversion: Converts time from one time system or format to another time system or format