C     ****
C     ****     /TERP/QUANTITIES NEEDED TO TRANSFORM SCALAR FIELDS
C     ****       BETWEEN GEOGRAPHIC AND GEOMAGNETIC COORDINATE SYSTEMS.
C     ****       THESE ARE CALCULATED BY:
C     ****       GRDSTM (GEOGRAPHIC TO GEOMAGMETIC) AND
C     ****       GRDSET (GEOMAGNETIC TO GEOGRAPHIC)
C     ****
      integer :: ig,jg,im,jm
      real :: wt,dim,djm
      COMMON/TERP/IG(IMAXMP,JMAXM),JG(IMAXMP,JMAXM),WT(4,IMAXMP,JMAXM),
     1  IM(ZIMXP1,0:ZJMXP1),JM(ZIMXP1,0:ZJMXP1),DIM(ZIMXP1,0:ZJMXP1),
     2  DJM(ZIMXP1,0:ZJMXP1)
C     ****
C     ****     WHERE:
C     ****       ZIMX=72, ZJMX=36, IMAXM=80, JMAXM=97, ZIMXP1=ZIMX+1,
C     ****         ZJMXP1=ZJMX+1,IMAXMP=IMAXM+1
C     ****       IG AND JG GIVE GEOGRAPHIC GRID ELEMENT CONTAINING
C     ****         EACH EACH GEOMAGNETIC GRID POINT.
C     ****       WT(4) = INTERPOLATION WEIGHTS TO BE APPLIED TO
C     ****         FUNCTION VALUES AT 4 CORNERS OF GEOGRAPHIC GRID
C     ****         ELEMENT (IG,JG)
C     ****       IM AND JM DEFINE GEOMAGNETIC GRID ELEMENT CONTAINING
C     ****         EACH GEOGRAPHIC GRID POINT.
C     ****       DIM AND DJM ARE FRACTIONS IN I AND J DIRECTIONS USED
C     ****         FOR BILINEAR INTERPOLATION IN GEOMAGNETIC GRID
C     ****         ELEMENT.
C     ****
C