ip_mercator_grid_mod.F90

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module ip_mercator_grid_mod
  use ip_grid_descriptor_mod
  use ip_grid_mod
  use ip_constants_mod, only: dpr, pi
  use earth_radius_mod
  implicit none
 
  private
  public :: ip_mercator_grid
 
  type, extends(ip_grid) :: ip_mercator_grid
     real :: rlat1
     real :: rlon1
     real :: rlon2
     real :: rlati
     real :: hi
     real :: dlon
     real :: dphi
   contains
     procedure :: init_grib1
     procedure :: init_grib2
     procedure :: gdswzd => gdswzd_mercator 
  end type ip_mercator_grid
 
  REAL :: dlon
  REAL :: dphi
  REAL :: rerth
 
CONTAINS
 
  subroutine init_grib1(self, g1_desc)
    class(ip_mercator_grid), intent(inout) :: self
    type(grib1_descriptor), intent(in) :: g1_desc
 
    integer :: iscan, jscan
    real :: dy, hj
 
    associate(kgds => g1_desc%gds)
      self%rerth = 6.3712e6
      self%eccen_squared = 0.0
 
      self%IM=kgds(2)
      self%JM=kgds(3)
 
      self%RLAT1=kgds(4)*1.e-3
      self%RLON1=kgds(5)*1.e-3
      self%RLON2=kgds(8)*1.e-3
      self%RLATI=kgds(9)*1.e-3
 
      iscan=mod(kgds(11)/128,2)
      jscan=mod(kgds(11)/64,2)
 
      dy=kgds(13)
      self%HI=(-1.)**iscan
      hj=(-1.)**(1-jscan)
      self%DLON=self%HI*(mod(self%HI*(self%RLON2-self%RLON1)-1+3600,360.)+1)/(self%IM-1)
      self%DPHI=hj*dy/(self%RERTH*cos(self%RLATI/dpr))
 
      ! defaults
      self%iwrap = 0
      self%jwrap1 = 0
      self%jwrap2 = 0
      self%nscan = mod(kgds(11) / 32, 2)
      self%nscan_field_pos = self%nscan
      self%kscan = 0
 
      self%iwrap = nint(360 / abs(self%dlon))
      if (self%im < self%iwrap) self%iwrap = 0
    end associate
 
  end subroutine init_grib1
 
  subroutine init_grib2(self, g2_desc)
    class(ip_mercator_grid), intent(inout) :: self
    type(grib2_descriptor), intent(in) :: g2_desc
 
    integer :: iscan, jscan
    real :: hj, dy
 
    associate(igdtmpl => g2_desc%gdt_tmpl, igdtlen => g2_desc%gdt_len)
 
      call earth_radius(igdtmpl, igdtlen, self%rerth, self%eccen_squared)
 
      self%IM=igdtmpl(8)
      self%JM=igdtmpl(9)
 
      self%RLAT1=float(igdtmpl(10))*1.0e-6
      self%RLON1=float(igdtmpl(11))*1.0e-6
      self%RLON2=float(igdtmpl(15))*1.0e-6
      self%RLATI=float(igdtmpl(13))*1.0e-6
 
      iscan=mod(igdtmpl(16)/128,2)
      jscan=mod(igdtmpl(16)/64,2)
 
      dy=float(igdtmpl(19))*1.0e-3
      self%HI=(-1.)**iscan
      hj=(-1.)**(1-jscan)
      self%DLON=self%HI*(mod(self%HI*(self%RLON2-self%RLON1)-1+3600,360.)+1)/(self%IM-1)
      self%DPHI=hj*dy/(self%RERTH*cos(self%RLATI/dpr))
 
      self%jwrap1 = 0
      self%jwrap2 = 0
      self%kscan = 0
      self%nscan=mod(igdtmpl(16) / 32,2)
      self%nscan_field_pos = self%nscan
 
      self%iwrap = nint(360 / abs(self%dlon))
      if(self%im < self%iwrap) self%iwrap = 0
 
    end associate
  end subroutine init_grib2
 
  SUBROUTINE gdswzd_mercator(self,IOPT,NPTS,FILL, &
       XPTS,YPTS,RLON,RLAT,NRET, &
       CROT,SROT,XLON,XLAT,YLON,YLAT,AREA)
    IMPLICIT NONE
    !
    class(ip_mercator_grid), intent(in) :: self
    INTEGER,           INTENT(IN   ) :: IOPT, NPTS
    INTEGER,           INTENT(  OUT) :: NRET
    !
    REAL,              INTENT(IN   ) :: FILL
    REAL,              INTENT(INOUT) :: RLON(NPTS),RLAT(NPTS)
    REAL,              INTENT(INOUT) :: XPTS(NPTS),YPTS(NPTS)
    REAL, OPTIONAL,    INTENT(  OUT) :: CROT(NPTS),SROT(NPTS)
    REAL, OPTIONAL,    INTENT(  OUT) :: XLON(NPTS),XLAT(NPTS)
    REAL, OPTIONAL,    INTENT(  OUT) :: YLON(NPTS),YLAT(NPTS),AREA(NPTS)
    !
    INTEGER                          :: IM, JM, N
    !
    LOGICAL                          :: LROT, LMAP, LAREA
    !
    REAL                             :: HI
    REAL                             :: RLAT1, RLON1, RLON2, RLATI
    REAL                             :: XMAX, XMIN, YMAX, YMIN
    REAL                             :: YE
    ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    IF(PRESENT(crot)) crot=fill
    IF(PRESENT(srot)) srot=fill
    IF(PRESENT(xlon)) xlon=fill
    IF(PRESENT(xlat)) xlat=fill
    IF(PRESENT(ylon)) ylon=fill
    IF(PRESENT(ylat)) ylat=fill
    IF(PRESENT(area)) area=fill
    ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 
    im=self%im
    jm=self%jm
 
    rlat1=self%rlat1
    rlon1=self%rlon1
    rlon2=self%rlon2
    rlati=self%rlati
 
    hi=self%hi
 
    dlon=self%dlon
    dphi=self%dphi
    rerth = self%rerth
 
    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
    IF(PRESENT(crot).AND.PRESENT(srot))THEN
       lrot=.true.
    ELSE
       lrot=.false.
    ENDIF
    IF(PRESENT(xlon).AND.PRESENT(xlat).AND.PRESENT(ylon).AND.PRESENT(ylat))THEN
       lmap=.true.
    ELSE
       lmap=.false.
    ENDIF
    IF(PRESENT(area))THEN
       larea=.true.
    ELSE
       larea=.false.
    ENDIF
    ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    !  TRANSLATE GRID COORDINATES TO EARTH COORDINATES
    IF(iopt.EQ.0.OR.iopt.EQ.1) THEN
       !$OMP PARALLEL DO PRIVATE(N) REDUCTION(+:NRET) SCHEDULE(STATIC)
       DO n=1,npts
          IF(xpts(n).GE.xmin.AND.xpts(n).LE.xmax.AND. &
               ypts(n).GE.ymin.AND.ypts(n).LE.ymax) THEN
             rlon(n)=mod(rlon1+dlon*(xpts(n)-1)+3600,360.)
             rlat(n)=2*atan(exp(dphi*(ypts(n)-ye)))*dpr-90
             nret=nret+1
             IF(lrot)  CALL mercator_vect_rot(crot(n),srot(n))
             IF(lmap)  CALL mercator_map_jacob(rlat(n),xlon(n),xlat(n),ylon(n),ylat(n))
             IF(larea) CALL mercator_grid_area(rlat(n),area(n))
          ELSE
             rlon(n)=fill
             rlat(n)=fill
          ENDIF
       ENDDO
       !$OMP END PARALLEL DO
       ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
       !  TRANSLATE EARTH COORDINATES TO GRID COORDINATES
    ELSEIF(iopt.EQ.-1) THEN
       !$OMP PARALLEL DO PRIVATE(N) REDUCTION(+:NRET) SCHEDULE(STATIC)
       DO n=1,npts
          IF(abs(rlon(n)).LE.360.AND.abs(rlat(n)).LT.90) THEN
             xpts(n)=1+hi*mod(hi*(rlon(n)-rlon1)+3600,360.)/dlon
             ypts(n)=ye+log(tan((rlat(n)+90)/2/dpr))/dphi
             IF(xpts(n).GE.xmin.AND.xpts(n).LE.xmax.AND. &
                  ypts(n).GE.ymin.AND.ypts(n).LE.ymax) THEN
                nret=nret+1
                IF(lrot)  CALL mercator_vect_rot(crot(n),srot(n))
                IF(lmap)  CALL mercator_map_jacob(rlat(n),xlon(n),xlat(n),ylon(n),ylat(n))
                IF(larea) CALL mercator_grid_area(rlat(n),area(n))
             ELSE
                xpts(n)=fill
                ypts(n)=fill
             ENDIF
          ELSE
             xpts(n)=fill
             ypts(n)=fill
          ENDIF
       ENDDO
       !$OMP END PARALLEL DO
    ENDIF
    ! - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  END SUBROUTINE gdswzd_mercator
 
  SUBROUTINE mercator_vect_rot(CROT,SROT)
    IMPLICIT NONE
 
    REAL,                INTENT(  OUT) :: CROT, SROT
 
    crot=1.0
    srot=0.0
 
  END SUBROUTINE mercator_vect_rot
 
  SUBROUTINE mercator_map_jacob(RLAT,XLON,XLAT,YLON,YLAT)
    IMPLICIT NONE
 
    REAL,                INTENT(IN   ) :: RLAT
    REAL,                INTENT(  OUT) :: XLON, XLAT, YLON, YLAT
 
    xlon=1./dlon
    xlat=0.
    ylon=0.
    ylat=1./dphi/cos(rlat/dpr)/dpr
 
  END SUBROUTINE mercator_map_jacob
 
  SUBROUTINE mercator_grid_area(RLAT,AREA)
    IMPLICIT NONE
 
    REAL,              INTENT(IN   ) :: RLAT
    REAL,              INTENT(  OUT) :: AREA
 
    area=rerth**2*cos(rlat/dpr)**2*dphi*dlon/dpr
 
  END SUBROUTINE mercator_grid_area
 
end module ip_mercator_grid_mod