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C Copyright 1981-2007 ECMWF
C
C Licensed under the GNU Lesser General Public License which
C incorporates the terms and conditions of version 3 of the GNU
C General Public License.
C See LICENSE and gpl-3.0.txt for details.
C
SUBROUTINE EULAVGG(NEWFLD, NEXT, INROW, RLAT, RLON,
X POLELAT, POLELON, FIELD, NGAUSS, TYPE)
C
C---->
C**** EULAVGG
C
C PURPOSE
C _______
C
C Generates values along a latitude in a rotated gaussian grid.
C (reverses the operations carried out by GGVALUE).
C
C INTERFACE
C _________
C
C CALL EULAVGG(NEWFLD, NEXT, INROW, RLAT, RLON,
C X POLELAT, POLELON, FIELD, NGAUSS, TYPE)
C
C
C Input parameters
C ________________
C
C NEWFLD - the field of values being created
C NEXT - start offset of the latitude row being created
C INROW - the number of points in the latitude row
C RLAT = target point latitude in the rotated grid
C RLON = target point longitude in the rotated grid
C POLELAT = latitude of the rotated South Pole
C POLELON = longitude of the rotated South Pole
C FIELD = original unrotated gaussian field values
C NGAUSS = original unrotated gaussian field number
C TYPE = original unrotated gaussian field type
C = 'F' for full (regular) gaussian field
C = 'R' for reduced (quasi) gaussian field
C
C Output parameters
C ________________
C
C NEWFLD(NEXT) to NEWFLD(NEXT+INROW-1) contains the latitude row
C values.
C
C
C METHOD
C ______
C
C Rotates the lat/long positions of points along the latitude row
C in a rotated gaussian grid back to positions in the unrotated grid
C and then interpolates vsalue from the original grid.
C
C
C EXTERNALS
C _________
C
C LL2XYZ - Converts a latitude/longitude position to (x,y,z)
C wrt axes through the centre of the globe. The z-axis
C runs from the south to north pole. The x- and y-axes
C are in the plane of the equator with the x-axis
C pointing out through lat/long (0,0).
C YROTATE - Rotates the globe about the y-axis.
C XYZ2LL - Converts an (x,y,z) position to a latitude/longitude.
C GGINTRP - Interpolates a value from an existing grid.
C
C
C REFERENCE
C _________
C
C None
C
C
C COMMENTS
C ________
C
C The input field is assumed to be global in extent, and a known
C definition, either N160 or N80 (reduced or regular).
C
C
C AUTHOR
C ______
C
C J.D.Chambers ECMWF April 1996
C
C
C MODIFICATIONS
C _____________
C
C None.
C
C----<
C _______________________________________________________
C
C* Section 0. Definition of variables.
C _______________________________________________________
C
IMPLICIT NONE
C
C Function arguments
REAL NEWFLD, RLAT, RLON, POLELAT, POLELON, FIELD
DIMENSION NEWFLD(*), RLON(*), FIELD(*)
INTEGER NEXT, INROW, NGAUSS
CHARACTER*1 TYPE
C
C Parameters
INTEGER JPMAXGG
PARAMETER( JPMAXGG = 1280 )
C
C Local variables
REAL X(JPMAXGG), Y(JPMAXGG), Z(JPMAXGG)
REAL RX(JPMAXGG),RY(JPMAXGG),RZ(JPMAXGG)
REAL OLAT(JPMAXGG),OLON(JPMAXGG)
INTEGER LOOP
C
C Adjust the target row points longitude to add back the longitude
C rotation
DO LOOP = 1, INROW
OLON(LOOP) = RLON(LOOP) - POLELON
IF( OLON(LOOP).LT.0.0 ) OLON(LOOP) = OLON(LOOP) + 360.0
IF( OLON(LOOP).GE.360.0 ) OLON(LOOP) = OLON(LOOP) - 360.0
ENDDO
C
C Convert the target row points lat/long to (x,y,z) coordinates
CALL LL2XYZ(RLAT,OLON,X,Y,Z,INROW)
C
C Rotate the target row points forward through the original latitude
C rotation
CALL YROTATE((90.0+POLELAT),X,Y,Z,RX,RY,RZ,INROW)
C
C Convert the target row points adjusted (x,y,z) coordinates to
C lat/long in the original grid (after longitude rotation)
CALL XYZ2LL(RX,RY,RZ,OLAT,OLON,INROW)
C
C Interpolate the rotated grid to the target row points
CALL GGINTRP(NEWFLD,NEXT,INROW,OLAT,OLON,FIELD,NGAUSS,TYPE)
C
RETURN
END
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