1FX(3NCARG) NCAR GRAPHICS FX(3NCARG)
2
6 FX - Given the X and Y coordinates of a point in the grid coordinate
7 system, the function FX returns the X coordinate of the point in user
8 coordinate space.
9 FY - Given the X and Y coordinates of a point in the grid coordinate
11 system, the function FY returns the Y coordinate of the point in user
12 coordinate space.
13
15 FX and FY are obsolete, and are supported only to provide compatibility
16 with old NCAR Graphics codes. These functions are internally callable
17 from four NCAR Graphics utilities -- the Conrec and Conran families,
18 and Vectors and Streamlines. Since the Conpack utility has replaced
19 Conrec and Conran for the most part, little needs to be said about the
20 use of FX and FY in those utilities.
21 For Vectors and Streamlines, however, these routines have been required
23 in order to perform custom mappings of the data coordinate space until
24 Version 3.2, when new mapping routine were developed to deal more
25 robustly with non-linear transformations of vector components. In order
26 to ease the transition for users of the old packages who depend on
27 existing custom mappings using FX and FX, however, both utilities have
28 implemented a number of compatibility levels. By modifying the
29 compatibility mode parameter, CPM, you can choose to map coordinates
30 either using the old FX and FY routines, or using the new Version 3.2
31 routines.
32 If you need to create new custom coordinate space mappings, you should
34 use the new mapping methods and not use FX and FY, since the internal
35 support for mappings based on these functions is frozen at the present
36 level. Any improvements in the code will be directed towards users of
37 the new mapping routines only.
38
40 USERX = FX (X,Y)
41 USERY = FY (X,Y)
42
44 X (REAL, input): The X coordinate of a vector location in the
45 grid coordinate system.
46 Y (REAL, input) The Y coordinate of a vector location in the
48 grid coordinate system.
49
51 The user does not invoke the functions, FX and FY, directly. Instead
52 the functions are invoked internally by an NCAR Graphics utility in
53 order to convert a position in the grid coordinate system into user
54 coordinates. By default, calls to any of the primary entry points for
55 Vectors and Streamlines utilities that predate Version 3.2 (that is,
56 EZVEC, VELVEC, VELVCT, EZSTRM or STRMLN) use FX and FY to map from grid
57 to user coordinates. However, by appropriately setting the
58 compatibility mode parameter, CPM, the user can choose whether the FX
59 and FY functions or the new mapping routines are invoked when using any
60 of the primary entry points, current or obsolete, supported by Vectors
61 and Streamlines.
62 Unlike the Version 3.2 mapping routines, whose input coordinates are in
64 the data coordinate system, FX and FY take input in the grid coordinate
65 system. Therefore, any required conversions into the data coordinate
66 system must be performed within the function prior to the mapping into
67 user coordinates. Vectors and Streamlines both provide common blocks
68 (VVMAP and STMAP, respectively) that may be included by the FX and FY
69 functions to supply the information necessary to perform the conversion
70 into data coordinate space. No pre-defined mappings are supported using
71 FX and FY. The default versions of these functions simply perform an
72 identity mapping from grid to user coordinate space.
73 When Vectors employs FX and FY, it (alone) also requires the use of two
75 other functions, called MXF and MYF. Their usage is described below:
76
78 MXF - MXF is a user modifiable function that, given one end point of a
79 vector in both grid and metacode coordinates, returns the X coordinate
80 of the other end of the vector in metacode coordinates.
81 MYF - MYF is a user modifiable function that, given one end point of a
83 vector in both grid and metacode coordinates, returns the Y coordinate
84 of the other end of the vector in metacode coordinates.
85
87 Like FX and FY, MXF and MYF are obsolete and should not be employed
88 when creating new custom mapping code.
89
91 METAX = MXF (X,Y,U,V,SFX,SFY,MX,MY)
92 METAY = MYF (X,Y,U,V,SFX,SFY,MX,MY)
93
95 X (REAL, input): The X coordinate of a vector location in the
96 grid coordinate system.
97 Y (REAL, input) The Y coordinate of a vector location in the
99 grid coordinate system.
100 U (REAL, input) The U component of the vector at the data
102 point specified by arguments X and Y.
103 V (REAL, input) The V component of the vector at the data
105 point specified by arguments X and Y.
106 SFX (REAL, input) Scale factor used to convert the vector
108 magnitude to a length in metacode coordinates.
109 SFY (REAL, input) Scale factor used to convert the vector
111 magnitude to a length in metacode coordinates. In the
112 current implementation this value is the same as the value
113 of SFX.
114 MX (INTEGER, input) X coordinate of the vector location in
116 metacode coordinates.
117 MX (INTEGER, input) Y coordinate of the vector location in
119 metacode coordinates.
120
122 The user does not invoke the functions, MXF and MYF, directly.
123 However, any time the Vectors utility is accessed with the
124 compatibility mode parameter set such that the FX and FY routines are
125 used to map the first endpoint of the vector, the functions MXF and MYF
126 are used to determine the second endpoint. First FX and FY are invoked
127 to determine the vector location in user coordinates, then this point
128 is converted into metacode coordinates; MXF and MYF are passed the
129 coordinates of the point both in grid space and in metacode space,
130 along with the vector components and a scale factor used to convert the
131 vector magnitude into a length in the metacode coordinate system.
132 The default version of MXF simply multiplies the U component of the
134 vector (the component parallel to the X grid axis) by the scale factor,
135 SFX, and adds it to the X coordinate of the first point in metacode
136 coordinates, MX. MYF uses the same scale factor, SFX, but multiplies by
137 the V component and adds to the Y coordinate in metacode coordinates.
138 These values are respectively returned as the function value by each
139 routine. Note that if a mapping is anywhere non-linear, the vector
140 directional angle may change across the transformation, and an
141 iterative differential technique must be employed to map the second
142 endpoint of the vector. When creating a new mapping, the user is
143 strongly urged to use the user-modifiable routine VVUMXY, rather than
144 attempting to work with MXF and MYF.
145
147 To use FX, FY, MXF, and MYF load the NCAR Graphics libraries ncarg,
148 ncarg_gks, and ncarg_c, preferably in that order.
149
151 Online: vectors, streamlines, vectors_params, streamlines_params,
152 vvumxy, stuixy, stumta, stumxy.
153
155 Copyright (C) 1987-2009
156 University Corporation for Atmospheric Research
157 The use of this Software is governed by a License Agreement.
158UNIX April 1993 FX(3NCARG)