Revision May 22, 2003

Changes made to eqvlat to accomodate the following special situations:

  1. if lat1 .eq. lat2, returned value will be lat1 (reduced to between -90.
     and 90.).
  2. If either lat1 or lat2 is 90. (or -90.) then 90. (or -90.) will be
     returned.  This reflects the fact that, for y fixed (-90. .lt. y .lt. 90.),
     as x -> 90. (or -90.), eqvlat(x,y) ->90. (or -90.)  This limiting
     case of tangent latitude 90. is a polar stereographic projection,
     for which the scale at 90. is a maximum, and therefore greater than the
     other latitude y.  Thus, eqvlat(90.,60.) returns 90., although the
     scale at 90. will be greater than at 60. For eqvlat(90.,-90.), the
     limit process is ambiguous; for the sake of symmetry, such a case
     will return 0.

Use of INCLUDE file cmapf.fi

PARAMETERs defined in cmapf.fi include PI, RADPDG (the number of radians in one
degree) DGPRAD (the number of degrees per radian) the default radius of the
Earth, and the size of the STCPRM arrays containing the projection information.

Instead of using REAL STCPRM(9), you can write

       INCLUDE 'cmapf.fi'
       REAL STCPRM(k_maparam)

to anticipate the possibility that the size of the STCPRM map paramater arrays
may change in future updates.


Revision Feb 12, 2002

To facilitate the transfer of vector wind data to and from Lat-Lon grids, we
have re-defined the behavior of the following SUBROUTINES:
CC2GXY, CG2CXY, CC2GLL, CG2CLL and CXY2LL.  We have also added the following new
routines: CG2WXY, CW2GXY, CG2WLL and CW2GLL.

The change in behavior applies only at, and within 1 degree (111 km) of, the
North and South poles.  Elsewhere, the behavior is unchanged.

Wind vector data, (U- and V- components) are transformed between three
coordinate systems:
(G, or Grid) - the U- and V- components are parallel to the x- and y- coordinate
	lines of the grid.
(C, or Cartographic):  U-component in the East direction, V in the North
	direction, except at the North and South Poles.
(W or WMO reporting convention): same as Cartographic, except that within one
	degree of the pole, wind reporting is revised by aligning a compass rose with
   "North" in the direction of the Greenwich meridian, and defining U- and V-
   components accordingly.

In a typical Lat-Lon grid, the row of the grid corresponding to the 90 or -90
	degree latitude has many separate points, all of which represent the North
   Pole but with different nominal longitudes.  The U- and V- components are
   specified as if on a compass rose, aligned with "South" toward the nominal
   longitude, and North toward the longitude 180 degrees away.  Thus, although
   it is the same wind at the same point, the U- and V- components differ
   depending on the longitude.  At the North pole, the gridded U-V values for
   the nominal 180 longitude correspond to the WMO standard, while at the South
   pole, a nominal 0 degree longitude will correspond to the WMO standard.

The behavior of the SUBROUTINES has been changed as follows:

CXY2LL(PARMAP,X,Y,XLAT,XLONG): 	Returns, as XLAT and XLONG, the latitude and
	longitude of the grid point whose coordinates are given by X,Y.  If XLAT=90.,
   XLONG will be set to 180.; if XLAT=-90., XLONG will be set to zero.
   Previously, at the poles, the returned value of XLONG was the value of REFLON
   which STLMBR used to initialize the projection.

CG2CLL(PARMAP,XLAT,XLONG, UG,VG, UE,VN), CC2GLL(PARMAP,XLAT,XLONG, UE,VN, UG,VG)
	Everywhere except at the poles, UE and VN are treated as the East and North
	components of the wind, respectively, corresponding to the wind with grid
   components UG,VG.  At the poles, UE and VN are components in the East and
   North direction of a compass rose aligned with the XLONG meridian.  This will
   allow the user to populate the points of a Lat-Lon grid according to the
   usual definitions.  Previously, within one degree (111km) of the poles, UE
   and VN were treated according to the WMO reporting convention.

CG2CXY(PARMAP, X,Y, UG,VG, UE,VN) and CC2GXY(PARMAP, X,Y, UE,VN, UG,VG):
	Everywhere except at the poles, UE and VN are treated as the East and North
   components of the wind, respectively, corresponding to the wind with grid
   components UG,VG.  At the poles, the UE and VN components are treated
   according to the WMO conventions, with a nominal longitude of 180 at the
   North Pole and 0 at the South Pole.  Previously, within one degree (111km) of
   the poles, UE and VN were treated according to the WMO reporting convention.

CG2WLL(PARMAP,XLAT,XLONG, UG,VG, UE,VN), CW2GLL(PARMAP,XLAT,XLONG, UE,VN, UG,VG)
CG2WXY(PARMAP, X,Y, UG,VG, UE,VN) and CW2GXY(PARMAP, X,Y, UE,VN, UG,VG):
	UE and VN will be treated as wind components based on the World
   Meteorological Organization (WMO) reporting standards.  That is, everywhere
   except within a radius of one degree (111km) of the poles, UE and VN are the
   East and North components of the wind, respectively, corresponding to the
   wind with grid components UG,VG. Within one degree of either pole, UE and VN
   will be components based on a compass rose oriented with "North" toward the
   Greenwich (0 degree) meridian).  This is the behavior previously defined for
   CG2CLL, CC2GLL, CG2CXY and CC2GXY.

Radius of the Earth has been reduced by 3.73 km to agree with that assumed for
   GRIB grids.  This will cause grids setup by stcm1p to cover a slightly larger
   range of latitudes and longitudes.