Standard Library procedure that draws a two-dimensional velocity fieldplot, with each directed arrow indicating the magnitude and direction of the field.
The x component of the two-dimensional field. This parameter must be a two-dimensional array.v
The y component of the two-dimensional field. This parameter must be a two-dimensional array of the same size as u.x
(optional) The abscissa values. This parameter must be a vector whose size equals the first dimension of u and v.y
(optional) The ordinate values. This parameter must be a vector whose size equals the second dimension of u and v.
If present and nonzero, places a dot at the position of the missing data. Otherwise, nothing is drawn for missing points. Dots is only valid if the Missing keyword is also specified.Length
A length factor. The default value is 1.0, which makes the longest (u, v) vector have a length equal to the length of a single cell.Missing
A two-dimensional array with the same size as the u and v arrays. It is used to specify that specific points have missing data.If the magnitude of the vector at (i, j) is less than the corresponding value in Missing, then the data is considered to be valid. Otherwise, the data is considered to be missing.
Thus, one way to set up a Missing array is to initialize all elements to some large value:
missing_array = FLTARR(n, m) + 1.0E30
missing_array(i, j) = -missing_array(i, j)
If missing values are present, you can use the Missing keyword to specify that they be ignored during the plotting, or the Dots keyword to specify that they be marked with a dot.
The system variables ![XY].Title and !P.Title may be used to title the axes and the main plot.
u = FLTARR(21, 21) v = FLTARR(21, 21)
.RUN
FOR j = 0, 20 DO BEGIN
FOR i = 0, 20 DO BEGIN
x = 0.05 * FLOAT(i)
z = 0.05 * FLOAT(j)
u(i, j) = -SIN(!Pi*x) * COS(!Pi*z)
v(i, j) = COS(!Pi*x) * SIN(!Pi*z)
ENDFOR
ENDFOR
END
VELOVECT, u, v
Figure 2-135 Velocity field displayed using default values.
Figure 2-136 Velocity field displayed using default values.
VELOVECT, u, v, Length=2
Figure 2-137 Velocity field displayed using arrows twice the length of a single cell.
Figure 2-138 Velocity field displayed using arrows twice the length of a single cell.
missing = FLTARR(21, 21) + 1.e30 missing(4:6, 7:9) = -1.e30 missing(15:17, 16:19) = -1.e30 VELOVECT, u, v, Missing=missing, /Dots
Figure 2-139 Velocity field that contains missing data.
Figure 2-140 Velocity field that contains missing data.
