## VELOVECT

The VELOVECT procedure produces a two-dimensional velocity field plot. A directed arrow is drawn at each point showing the direction and magnitude of the field.

This routine is written in the IDL language. Its source code can be found in the file ``` velovect.pro``` in the ``` lib``` subdirectory of the IDL distribution.

### Calling Sequence

VELOVECT, U, V [, X, Y]

### Arguments

#### U

The X component of the two-dimensional field. U must be a two-dimensional array.

#### V

The Y component of the two dimensional field. V must have the same dimensions as U .

#### X

Optional abcissae values. X must be a vector with a length equal to the first dimension of U and V .

#### Y

Optional ordinate values. Y must be a vector with a length equal to the second dimension of U and V .

### Keywords

NOTE: Keywords not described here are passed directly to the PLOT procedure and may be used to set options such as TITLE, POSITION, NOERASE, etc.

#### COLOR

Set this keyword equal to the color index used for the plot.

#### DOTS

Set this keyword to 1 to place a dot at each missing point. Set this keyword to 0 or omit it to draw nothing for missing points. Has effect only if MISSING is specified.

#### LENGTH

Set this keyword equal to the length factor. The default of 1.0 makes the longest ( U , V ) vector the length of a cell.

#### MISSING

Set this keyword equal to the missing data value. Vectors with a length greater than MISSING are ignored.

### PLOT Keywords

In addition to the keywords described above, all other keywords accepted by the PLOT procedure are accepted by VELOVECT. See PLOT .

### Example

U = RANDOMN(S, 20, 20) ; Create some random data.

V = RANDOMN(S, 20, 20)

VELOVECT, U, V ; Plot the vector field.

VELOVECT, U, V, MISSING=18, /DOTS ; Plot the field, using dots to represent vectors with values greater than 18.

VELOVECT, U, V, MISSING=18, /DOTS, XTITLE='Random Vectors'
; Plot with a title. Note that the XTITLE keyword is passed directly to the PLOT procedure.