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gdswizc9.f
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SUBROUTINE GDSWIZC9(KGDS,IOPT,NPTS,FILL,XPTS,YPTS,RLON,RLAT,NRET,
& LROT,CROT,SROT)
C$$$ SUBPROGRAM DOCUMENTATION BLOCK
C
C SUBPROGRAM: GDSWIZC9 GDS WIZARD FOR ROTATED EQUIDISTANT 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 STAGGERED ROTATED EQUIDISTANT CYLINDRICAL PROJECTIONS.
C (SEE UNDER THE DESCRIPTION OF KGDS TO DETERMINE WHETHER
C TO COMPUTE A STAGGERED WIND GRID OR A STAGGERED MASS GRID.)
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
C PROGRAM HISTORY LOG:
C 96-04-10 IREDELL
C
C USAGE: CALL GDSWIZC9(KGDS,IOPT,NPTS,FILL,XPTS,YPTS,RLON,RLAT,NRET,
C & LROT,CROT,SROT)
C
C INPUT ARGUMENT LIST:
C KGDS - INTEGER (200) GDS PARAMETERS AS DECODED BY W3FI63
C IMPORTANT NOTE: IF THE 9TH BIT (FROM RIGHT) OF KGDS(11)
C (SCANNING MODE FLAG) IS 1, THEN THIS
C THE GRID IS COMPUTED FOR A WIND FIELD;
C OTHERWISE IT IS FOR A MASS FIELD. THUS
C MOD(KGDS(11)/256,2)=0 FOR MASS GRID.
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
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
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)
PARAMETER(RERTH=6.3712E6)
PARAMETER(PI=3.14159265358979,DPR=180./PI)
C - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
IF(KGDS(1).EQ.201) THEN
RLAT1=KGDS(4)*1.E-3
RLON1=KGDS(5)*1.E-3
IROT=MOD(KGDS(6)/8,2)
IM=KGDS(7)*2-1
JM=KGDS(8)
DLON=KGDS(9)*1.E-3
DLAT=KGDS(10)*1.E-3
KSCAN=MOD(KGDS(11)/256,2)
ISCAN=MOD(KGDS(11)/128,2)
JSCAN=MOD(KGDS(11)/64,2)
NSCAN=MOD(KGDS(11)/32,2)
HI=(-1.)**ISCAN
HJ=(-1.)**(1-JSCAN)
DLONS=HI*DLON
DLATS=HJ*DLAT
RLONR=-(IM-1)/2*DLONS
RLATR=-(JM-1)/2*DLATS
SLAT1=SIN(RLAT1/DPR)
CLAT1=COS(RLAT1/DPR)
SLONR=SIN(RLONR/DPR)
CLONR=COS(RLONR/DPR)
SLATR=SIN(RLATR/DPR)
CLATR=COS(RLATR/DPR)
DENOM=1-(CLATR*SLONR)**2
SLAT0=(SLAT1*CLATR*CLONR-SLATR*SQRT(DENOM-SLAT1**2))/DENOM
CLAT0=SQRT(1-SLAT0**2)
RLON0=RLON1+HI*DPR*ACOS((CLAT0*CLATR*CLONR-SLAT0*SLATR)/CLAT1)
C THE FOLLOWING INDENTED LINES ARE A TEMPORARY FIX OF IMPRECISE GRID.
C CAUTION: CENTRAL LATITUDE AND LONGITUDE ARE ASSUMED TO BE INTEGERS.
SLAT0=SIN(NINT(ASIN(SLAT0)*DPR)/DPR)
CLAT0=SQRT(1-SLAT0**2)
RLON0=NINT(RLON0)
HS=SIGN(1.,MOD(RLON1-RLON0+180+3600,360.)-180)
CLON1=COS((RLON1-RLON0)/DPR)
SLATR=CLAT0*SLAT1-SLAT0*CLAT1*CLON1
CLATR=SQRT(1-SLATR**2)
CLONR=(CLAT0*CLAT1*CLON1+SLAT0*SLAT1)/CLATR
RLATR=DPR*ASIN(SLATR)
RLONR=HS*DPR*ACOS(CLONR)
DLATS=RLATR/(-(JM-1)/2)
DLONS=RLONR/(-(IM-1)/2)
IF(KSCAN.EQ.0) THEN
IS1=(JM+1)/2
ELSE
IS1=JM/2
ENDIF
XMIN=0
XMAX=IM+1
IF(IM.EQ.NINT(360/ABS(DLONS))) 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
XPTF=YPTS(N)+(XPTS(N)-IS1)
YPTF=YPTS(N)-(XPTS(N)-IS1)+KSCAN
IF(XPTF.GE.XMIN.AND.XPTF.LE.XMAX.AND.
& YPTF.GE.YMIN.AND.YPTF.LE.YMAX) THEN
HS=HI*SIGN(1.,XPTF-(IM+1)/2)
RLONR=(XPTF-(IM+1)/2)*DLONS
RLATR=(YPTF-(JM+1)/2)*DLATS
CLONR=COS(RLONR/DPR)
SLATR=SIN(RLATR/DPR)
CLATR=COS(RLATR/DPR)
SLAT=CLAT0*SLATR+SLAT0*CLATR*CLONR
IF(SLAT.LE.-1) THEN
CLAT=0.
CLON=COS(RLON0/DPR)
RLON(N)=0
RLAT(N)=-90
ELSEIF(SLAT.GE.1) THEN
CLAT=0.
CLON=COS(RLON0/DPR)
RLON(N)=0
RLAT(N)=90
ELSE
CLAT=SQRT(1-SLAT**2)
CLON=(CLAT0*CLATR*CLONR-SLAT0*SLATR)/CLAT
CLON=MIN(MAX(CLON,-1.),1.)
RLON(N)=MOD(RLON0+HS*DPR*ACOS(CLON)+3600,360.)
RLAT(N)=DPR*ASIN(SLAT)
ENDIF
NRET=NRET+1
IF(LROT.EQ.1) THEN
IF(IROT.EQ.1) THEN
IF(CLATR.LE.0) THEN
CROT(N)=-SIGN(1.,SLATR*SLAT0)
SROT(N)=0
ELSE
SLON=SIN((RLON(N)-RLON0)/DPR)
CROT(N)=(CLAT0*CLAT+SLAT0*SLAT*CLON)/CLATR
SROT(N)=SLAT0*SLON/CLATR
ENDIF
ELSE
CROT(N)=1
SROT(N)=0
ENDIF
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)).LE.90) THEN
HS=SIGN(1.,MOD(RLON(N)-RLON0+180+3600,360.)-180)
CLON=COS((RLON(N)-RLON0)/DPR)
SLAT=SIN(RLAT(N)/DPR)
CLAT=COS(RLAT(N)/DPR)
SLATR=CLAT0*SLAT-SLAT0*CLAT*CLON
IF(SLATR.LE.-1) THEN
CLATR=0.
RLONR=0
RLATR=-90
ELSEIF(SLATR.GE.1) THEN
CLATR=0.
RLONR=0
RLATR=90
ELSE
CLATR=SQRT(1-SLATR**2)
CLONR=(CLAT0*CLAT*CLON+SLAT0*SLAT)/CLATR
CLONR=MIN(MAX(CLONR,-1.),1.)
RLONR=HS*DPR*ACOS(CLONR)
RLATR=DPR*ASIN(SLATR)
ENDIF
XPTF=(IM+1)/2+RLONR/DLONS
YPTF=(JM+1)/2+RLATR/DLATS
IF(XPTF.GE.XMIN.AND.XPTF.LE.XMAX.AND.
& YPTF.GE.YMIN.AND.YPTF.LE.YMAX) THEN
XPTS(N)=IS1+(XPTF-(YPTF-KSCAN))/2
YPTS(N)=(XPTF+(YPTF-KSCAN))/2
NRET=NRET+1
IF(LROT.EQ.1) THEN
IF(IROT.EQ.1) THEN
IF(CLATR.LE.0) THEN
CROT(N)=-SIGN(1.,SLATR*SLAT0)
SROT(N)=0
ELSE
SLON=SIN((RLON(N)-RLON0)/DPR)
CROT(N)=(CLAT0*CLAT+SLAT0*SLAT*CLON)/CLATR
SROT(N)=SLAT0*SLON/CLATR
ENDIF
ELSE
CROT(N)=1
SROT(N)=0
ENDIF
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