w3fb02.f

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C> @file
C> @brief COnvert s. hemisphere lat/lon to i and j.
C> @author Ralph Jones @date 1985-09-13
 
C> Computes i and j coordinates for a latitude/longitude
C> point on the southern hemisphere polar stereographic map
C> projection.
C>
C> Program history log:
C> - Ralph Jones 1985-09-13 Convert to fortran 77.
C> - Ralph Jones 1990-08-31 Convert to cray cft77 fortran.
C>
C> @param[in] ALAT Real*4 latitude (s.h. latitudes are negative)
C> @param[in] ALONG Real*4 west longitude.
C> @param[in] XMESHL Real*4 grid interval in km.
C> @param[out] XI Real*4 i coordinate.
C> @param[out] XJ Real*4 j coordinate.
C>
C> @author Ralph Jones @date 1985-09-13
      SUBROUTINE w3fb02(ALAT, ALONG, XMESHL, XI, XJ)
C
C     ...GIVEN ... ALAT   SRN HEMI LATS ARE NEGATIVE VALUED
C                  ALONG   IN DEGREES  WEST LONGITUDE
C                  XMESHL= GRID INTERVAL IN KM,  E.G., 381.0 KM
C     ...TO COMPUTE XI,XJ FOR A PT ON THE SRN HEMI POLAR STEREOGRAPHIC
C     ...   PROJECTION, WITH 80W LONGITUDE VERTICAL AT THE TOP OF  MAP,
C     ...   AND 100E LONGITUDE VERTICAL AT THE BOTTOM OF THE MAP.
C     ...THE RESULTING XI AND XJ ARE RELATIVE TO  (0,0) AT SOUTH POLE.
C
       DATA  addlng/80.0/
C
C     ...WHICH IS DIFFERENCE BETWEEN 180 DEGREES AND VERTICAL MERIDIAN.
C     ...   THE VERTICAL BEING 100 WEST AFTER CHANGING THE SENSE
C
       DATA  tiny  /0.00001/
       DATA  earthr/6371.2/
       DATA  convt /0.017453293/
C
C     ...WHICH CONVERTS DEGREES TO RADIANS
C
      re   = (earthr * 1.86603) / xmeshl
C
C     ...WHICH IS DISTANCE IN GRID INTERVALS FROM POLE TO  EQUATOR
C
      xlat = -alat * convt
C
C     ...WHERE NEGATIVE ALATS WERE GIVEN FOR SRN HEMI
C
      wlong = 360.0 - along
      wlong = (wlong + addlng) * convt
      r     = (re * cos(xlat))/(1.0 + sin(xlat))
      xi    = r * sin(wlong)
      IF (abs(xi) .LT. tiny) xi = 0.0
      xj    = r * cos(wlong)
      IF (abs(xj) .LT. tiny) xj = 0.0
      RETURN
      END