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gdswzd01.f
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C-----------------------------------------------------------------------
SUBROUTINE GDSWZD01(KGDS,IOPT,NPTS,FILL,XPTS,YPTS,RLON,RLAT,NRET,
& LROT,CROT,SROT,LMAP,XLON,XLAT,YLON,YLAT,AREA)
C$$$ SUBPROGRAM DOCUMENTATION BLOCK
C
C SUBPROGRAM: GDSWZD01 GDS WIZARD FOR MERCATOR CYLINDRICAL
C PRGMMR: IREDELL ORG: W/NMC23 DATE: 96-04-10
C
C ABSTRACT: THIS SUBPROGRAM DECODES THE GRIB GRID DESCRIPTION SECTION
C (PASSED IN INTEGER FORM AS DECODED BY SUBPROGRAM W3FI63)
C AND RETURNS ONE OF THE FOLLOWING:
C (IOPT=+1) EARTH COORDINATES OF SELECTED GRID COORDINATES
C (IOPT=-1) GRID COORDINATES OF SELECTED EARTH COORDINATES
C FOR MERCATOR CYLINDRICAL PROJECTIONS.
C IF THE SELECTED COORDINATES ARE MORE THAN ONE GRIDPOINT
C BEYOND THE THE EDGES OF THE GRID DOMAIN, THEN THE RELEVANT
C OUTPUT ELEMENTS ARE SET TO FILL VALUES.
C THE ACTUAL NUMBER OF VALID POINTS COMPUTED IS RETURNED TOO.
C OPTIONALLY, THE VECTOR ROTATIONS AND THE MAP JACOBIANS
C FOR THIS GRID MAY BE RETURNED AS WELL.
C
C PROGRAM HISTORY LOG:
C 96-04-10 IREDELL
C 96-10-01 IREDELL PROTECTED AGAINST UNRESOLVABLE POINTS
C 97-10-20 IREDELL INCLUDE MAP OPTIONS
C
C USAGE: CALL GDSWZD01(KGDS,IOPT,NPTS,FILL,XPTS,YPTS,RLON,RLAT,NRET,
C & LROT,CROT,SROT,LMAP,XLON,XLAT,YLON,YLAT,AREA)
C
C INPUT ARGUMENT LIST:
C KGDS - INTEGER (200) GDS PARAMETERS AS DECODED BY W3FI63
C IOPT - INTEGER OPTION FLAG
C (+1 TO COMPUTE EARTH COORDS OF SELECTED GRID COORDS)
C (-1 TO COMPUTE GRID COORDS OF SELECTED EARTH COORDS)
C NPTS - INTEGER MAXIMUM NUMBER OF COORDINATES
C FILL - REAL FILL VALUE TO SET INVALID OUTPUT DATA
C (MUST BE IMPOSSIBLE VALUE; SUGGESTED VALUE: -9999.)
C XPTS - REAL (NPTS) GRID X POINT COORDINATES IF IOPT>0
C YPTS - REAL (NPTS) GRID Y POINT COORDINATES IF IOPT>0
C RLON - REAL (NPTS) EARTH LONGITUDES IN DEGREES E IF IOPT<0
C (ACCEPTABLE RANGE: -360. TO 360.)
C RLAT - REAL (NPTS) EARTH LATITUDES IN DEGREES N IF IOPT<0
C (ACCEPTABLE RANGE: -90. TO 90.)
C LROT - INTEGER FLAG TO RETURN VECTOR ROTATIONS IF 1
C LMAP - INTEGER FLAG TO RETURN MAP JACOBIANS IF 1
C
C OUTPUT ARGUMENT LIST:
C XPTS - REAL (NPTS) GRID X POINT COORDINATES IF IOPT<0
C YPTS - REAL (NPTS) GRID Y POINT COORDINATES IF IOPT<0
C RLON - REAL (NPTS) EARTH LONGITUDES IN DEGREES E IF IOPT>0
C RLAT - REAL (NPTS) EARTH LATITUDES IN DEGREES N IF IOPT>0
C NRET - INTEGER NUMBER OF VALID POINTS COMPUTED
C CROT - REAL (NPTS) CLOCKWISE VECTOR ROTATION COSINES IF LROT=1
C SROT - REAL (NPTS) CLOCKWISE VECTOR ROTATION SINES IF LROT=1
C (UGRID=CROT*UEARTH-SROT*VEARTH;
C VGRID=SROT*UEARTH+CROT*VEARTH)
C XLON - REAL (NPTS) DX/DLON IN 1/DEGREES IF LMAP=1
C XLAT - REAL (NPTS) DX/DLAT IN 1/DEGREES IF LMAP=1
C YLON - REAL (NPTS) DY/DLON IN 1/DEGREES IF LMAP=1
C YLAT - REAL (NPTS) DY/DLAT IN 1/DEGREES IF LMAP=1
C AREA - REAL (NPTS) AREA WEIGHTS IN M**2 IF LMAP=1
C (PROPORTIONAL TO THE SQUARE OF THE MAP FACTOR)
C
C ATTRIBUTES:
C LANGUAGE: FORTRAN 77
C
C$$$
INTEGER KGDS(200)
REAL XPTS(NPTS),YPTS(NPTS),RLON(NPTS),RLAT(NPTS)
REAL CROT(NPTS),SROT(NPTS)
REAL XLON(NPTS),XLAT(NPTS),YLON(NPTS),YLAT(NPTS),AREA(NPTS)
PARAMETER(RERTH=6.3712E6)
PARAMETER(PI=3.14159265358979,DPR=180./PI)
C - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
IF(KGDS(1).EQ.001) THEN
IM=KGDS(2)
JM=KGDS(3)
RLAT1=KGDS(4)*1.E-3
RLON1=KGDS(5)*1.E-3
RLAT2=KGDS(7)*1.E-3
RLON2=KGDS(8)*1.E-3
RLATI=KGDS(9)*1.E-3
ISCAN=MOD(KGDS(11)/128,2)
JSCAN=MOD(KGDS(11)/64,2)
NSCAN=MOD(KGDS(11)/32,2)
DX=KGDS(12)
DY=KGDS(13)
HI=(-1.)**ISCAN
HJ=(-1.)**(1-JSCAN)
DLON=HI*(MOD(HI*(RLON2-RLON1)-1+3600,360.)+1)/(IM-1)
DPHI=HJ*DY/(RERTH*COS(RLATI/DPR))
YE=1-LOG(TAN((RLAT1+90)/2/DPR))/DPHI
XMIN=0
XMAX=IM+1
IF(IM.EQ.NINT(360/ABS(DLON))) XMAX=IM+2
YMIN=0
YMAX=JM+1
NRET=0
C - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
C TRANSLATE GRID COORDINATES TO EARTH COORDINATES
IF(IOPT.EQ.0.OR.IOPT.EQ.1) THEN
DO N=1,NPTS
IF(XPTS(N).GE.XMIN.AND.XPTS(N).LE.XMAX.AND.
& YPTS(N).GE.YMIN.AND.YPTS(N).LE.YMAX) THEN
RLON(N)=MOD(RLON1+DLON*(XPTS(N)-1)+3600,360.)
RLAT(N)=2*ATAN(EXP(DPHI*(YPTS(N)-YE)))*DPR-90
NRET=NRET+1
IF(LROT.EQ.1) THEN
CROT(N)=1
SROT(N)=0
ENDIF
IF(LMAP.EQ.1) THEN
XLON(N)=1/DLON
XLAT(N)=0.
YLON(N)=0.
YLAT(N)=1/DPHI/COS(RLAT(N)/DPR)/DPR
AREA(N)=RERTH**2*COS(RLAT(N)/DPR)**2*DPHI*DLON/DPR
ENDIF
ELSE
RLON(N)=FILL
RLAT(N)=FILL
ENDIF
ENDDO
C - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
C TRANSLATE EARTH COORDINATES TO GRID COORDINATES
ELSEIF(IOPT.EQ.-1) THEN
DO N=1,NPTS
IF(ABS(RLON(N)).LE.360.AND.ABS(RLAT(N)).LT.90) THEN
XPTS(N)=1+HI*MOD(HI*(RLON(N)-RLON1)+3600,360.)/DLON
YPTS(N)=YE+LOG(TAN((RLAT(N)+90)/2/DPR))/DPHI
IF(XPTS(N).GE.XMIN.AND.XPTS(N).LE.XMAX.AND.
& YPTS(N).GE.YMIN.AND.YPTS(N).LE.YMAX) THEN
NRET=NRET+1
IF(LROT.EQ.1) THEN
CROT(N)=1
SROT(N)=0
ENDIF
IF(LMAP.EQ.1) THEN
XLON(N)=1/DLON
XLAT(N)=0.
YLON(N)=0.
YLAT(N)=1/DPHI/COS(RLAT(N)/DPR)/DPR
AREA(N)=RERTH**2*COS(RLAT(N)/DPR)**2*DPHI*DLON/DPR
ENDIF
ELSE
XPTS(N)=FILL
YPTS(N)=FILL
ENDIF
ELSE
XPTS(N)=FILL
YPTS(N)=FILL
ENDIF
ENDDO
ENDIF
C - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
C PROJECTION UNRECOGNIZED
ELSE
IRET=-1
IF(IOPT.GE.0) THEN
DO N=1,NPTS
RLON(N)=FILL
RLAT(N)=FILL
ENDDO
ENDIF
IF(IOPT.LE.0) THEN
DO N=1,NPTS
XPTS(N)=FILL
YPTS(N)=FILL
ENDDO
ENDIF
ENDIF
C - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
END