DESIGNATE PLANETOCENTRIC

Syntax

Fixed

   DESIGNATE @int(1001:10099)
      CENTER @body
      REFERENCE PLANETOCENTRIC
      (2:3){ LATITUDE  @number
           | LONGITUDE @number
           | @options
           | RADIUS    @number }
      (0:3){ FROM  @calendar
           | TO    @calendar
           | EPOCH @calendar }

Moving

   DESIGNATE @int(1001:10099)
      CENTER @body
      REFERENCE PLANETOCENTRIC
      (2:3){ LATITUDE  (1:2)@number
           | LONGITUDE (1:2)@number
           | @options
           | RADIUS    (1:2)@number }
      EPOCH @calendar
      (0:2){ FROM @calendar
           | TO   @calendar }

Description

When creating a designated object in this system, you must specify the latitude and longitude of the object. The radius is optional, and defaults to the largest semi-major axis of the tri-axial ellipsoid used to model the body.

Definition

In planetocentric coordinates, the z-axis points toward the north pole of the reference body. The x-axis is defined by the intersection of the equator and prime meridian of the body. The origin is at the center of the body.

Let P be a point in space, and let V be the position vector from the origin of the planetocentric frame to P.

The planetocentric latitude of P is the angle between the equator and V. North latitudes are positive, south latitudes are negative.

The planetocentric longitude of P is the angle between the x-axis and the projection of V onto the x-y plane, positive from x toward y.

The planetocentric radius of P is the distance from the center of the reference body to P (the magnitude of V).

Examples

   ;
   ;   Define a name for the designated object (the Great Dark Spot
   ;   on Neptune).
   ;
   DEFINE 1001 NEPTUNE_SPOT;
 
   ;
   ;   Provide the location of the spot. Note that the longitude
   ;   changes with time.
   ;
   DESIGNATE NEPTUNE_SPOT
        CENTER NEPTUNE
        REFERENCE  PLANETOCENTRIC
        LATITUDE -25 DEGREES;
        LONGITUDE 175 DEGREES -2 DEGREES/HOUR
        RADIUS 24270 KM
        EPOCH 23 MAY 1991 10:11:05;
 
   ;
   ;   Find intervals when the spot is in transit across Neptune
   ;   (that is, when it is visible from Earth).
   ;
    FIND VISIBLE TRANSIT OF NEPTUNE_SPOT
        ACROSS NEPTUNE FROM EARTH;