DESIGNATE MAGNETIC

Syntax

Fixed

   DESIGNATE @int(1001:10099)
        CENTER @body
        REFERENCE MAGNETIC
        (3:3){ LATITUDE  @number
             | LONGITUDE @number
             | RADIUS    @number }
        (0:5){ POLAR  LATITUDE  @number
             | POLAR  LONGITUDE @number
             | ORIGIN LONGITUDE @number
             | ORIGIN LATITUDE  @number
             | ORIGIN RADIUS    @number }
        (0:3){ FROM  @calendar
             | TO    @calendar
             | EPOCH @calendar }

Moving

   DESIGNATE @int(1001:10099)
        CENTER @body
        REFERENCE MAGNETIC
        (3:3){ LATITUDE  (1:2)@number
             | LONGITUDE (1:2)@number
             | RADIUS    (1:2)@number }
        (0:5){ POLAR  LATITUDE  @number
             | POLAR  LONGITUDE @number
             | ORIGIN LONGITUDE @number
             | ORIGIN LATITUDE  @number
             | ORIGIN RADIUS    @number }
        EPOCH @calendar
        (0:2){ FROM  @calendar
             | TO    @calendar }

Description

When creating a designated object in this system, you must specify the latitude, longitude, and radius of the object within the magnetic reference frame. You may also define the frame itself by specifying a tilt and offset.

Informal definition

Start with the cartographic frame attached to the reference body. Tilt the frame so that the north pole (the positive z-axis) runs through some latitude and longitude, and so that the x-z plane contains the cartographic x-axis. Now move the frame to center it at some point away from the center of the reference body. The new frame is fixed to the reference body and swings around as the body rotates.

Formal definition

Let the magnetic frame be defined as follows:

   POLAR  LATITUDE  = A
   POLAR  LONGITUDE = B
   ORIGIN LONGITUDE = C
   ORIGIN LATITUDE  = D
   ORIGIN RADIUS    = E

If A is 90 degrees and E is zero, the magnetic and cartographic frames are identical.

If A is not 90 degrees then A and B define a point in cartographic coordinates on the surface of the reference body that is not the cartographic north. The z-axis of the magnetic fr vector from the center of the body to this point.

Cross the magnetic z-axis with the cartographic x-axis to get the magnetic y-axis. Cross the magnetic y-axis with the magnetic z-axis to get the magnetic x-axis.

If E is not zero, then C, D and E define a point in cartographic coordinates some distance and direction from the center of the reference body. The origin of the magnetic frame is fixed at this point.

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

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

The magnetic longitude of P is the angle between the x-axis and the projection of V onto the x-y plane. (Longitude is negative from x toward y for bodies with direct rotation, but positive from x toward y for bodies with retrograde rotation.)

The magnetic radius of P is the distance from the origin of the magnetic frame to P (the magnitude of V).

Default values

If the tilt and offset terms that define the magnetic frame are not supplied, they default to the nominal values for the Jupiter magnetic coordinate frame:

   ORIGIN LONGITUDE   0
   ORIGIN LATITUDE    0
   ORIGIN RADIUS      0
   POLAR  LATITUDE   83 DEGREES
   POLAR  LONGITUDE 202 DEGREES

Examples

   ;
   ;   Place a designated object at the north magnetic pole
   ;   of Jupiter.
   ;
   DEFINE MAGNETIC_POLE  1001;
   DEFINE JUPITER_RADIUS 71400 KM;
 
   DESIGNATE MAGNETIC_POLE
        CENTER           JUPITER
        REFERENCE       MAGNETIC
        LATITUDE      90 DEGREES
        LONGITUDE      0 DEGREES
        RADIUS    JUPITER_RADIUS;