FX - Given the X and Y coordinates of a point in the grid coordinate system, the function FX returns the

       To use FX, FY, MXF, and MYF load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c, preferably in
       that order.

       Copyright (C) 1987-2009
       University Corporation for Atmospheric Research
       The use of this Software is governed by a License Agreement.

UNIX                                               April 1993                                         FX(3NCARG)

       X           (REAL, input): The X coordinate of a vector location in the grid coordinate system.

       Y           (REAL, input) The Y coordinate of a vector location in the grid coordinate system.

       U           (REAL, input) The U component of the vector at the data point specified by arguments X and Y.

       V           (REAL, input) The V component of the vector at the data point specified by arguments X and Y.

       SFX         (REAL,  input)  Scale  factor  used  to  convert the vector magnitude to a length in metacode
                   coordinates.

       SFY         (REAL, input) Scale factor used to convert the vector  magnitude  to  a  length  in  metacode
                   coordinates. In the current implementation this value is the same as the value of SFX.

       MX          (INTEGER, input) X coordinate of the vector location in metacode coordinates.

       MX          (INTEGER, input) Y coordinate of the vector location in metacode coordinates.

       MXF - MXF is a user modifiable function that, given one end point of a vector in both grid  and  metacode
       coordinates, returns the X coordinate of the other end of the vector in metacode coordinates.

       MYF  -  MYF is a user modifiable function that, given one end point of a vector in both grid and metacode
       coordinates, returns the Y coordinate of the other end of the vector in metacode coordinates.

       Online: vectors, streamlines, vectors_params, streamlines_params, vvumxy, stuixy, stumta, stumxy.

       Like FX and FY, MXF and MYF are obsolete and should not be employed  when  creating  new  custom  mapping
       code.

       METAX = MXF (X,Y,U,V,SFX,SFY,MX,MY)
       METAY = MYF (X,Y,U,V,SFX,SFY,MX,MY)

       The  user does not invoke the functions, MXF and MYF, directly.  However, any time the Vectors utility is
       accessed with the compatibility mode parameter set such that the FX and FY routines are used to  map  the
       first endpoint of the vector, the functions MXF and MYF are used to determine the second endpoint.  First
       FX  and FY are invoked to determine the vector location in user coordinates, then this point is converted
       into metacode coordinates; MXF and MYF are passed the coordinates of the point both in grid space and  in
       metacode  space, along with the vector components and a scale factor used to convert the vector magnitude
       into a length in the metacode coordinate system.

       The default version of MXF simply multiplies the U component of the vector (the component parallel to the
       X grid axis) by the scale factor, SFX, and adds it to the X coordinate of the  first  point  in  metacode
       coordinates, MX. MYF uses the same scale factor, SFX, but multiplies by the V component and adds to the Y
       coordinate  in metacode coordinates. These values are respectively returned as the function value by each
       routine. Note that if a mapping is anywhere non-linear, the vector directional angle  may  change  across
       the  transformation,  and an iterative differential technique must be employed to map the second endpoint
       of the vector. When creating a new mapping, the user is strongly urged to use the user-modifiable routine
       VVUMXY, rather than attempting to work with MXF and MYF.