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.

## Examples

; Create some random data:

U = RANDOMN(S, 20, 20)

V = RANDOMN(S, 20, 20)

; Plot the vector field:

VELOVECT, U, V

; Plot the field, using dots to represent vectors with values

; greater than 18:

VELOVECT, U, V, MISSING=18, /DOTS

; Plot with a title. Note that the XTITLE keyword is passed

; directly to the PLOT procedure:

VELOVECT, U, V, MISSING=18, /DOTS, XTITLE='Random Vectors'

## Syntax

VELOVECT, *U*, *V* [, *X*, *Y*] [, COLOR=*index*] [, MISSING=*value* [, /DOTS]] [, LENGTH=*value*] [, /OVERPLOT] [Also accepts all PLOT keywords]

## 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 abscissae 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.

### OVERPLOT

Set this keyword to make VELOVECT “overplot”. That is, the current graphics screen is not erased, no axes are drawn, and the previously established scaling remains in effect.

### PLOT Keywords Accepted

See PLOT Procedure for the description of the following plotting keywords:

ISOTROPIC, MAX_VALUE, MIN_VALUE, NSUM, POLAR, THICK, XLOG, YLOG, YNOZERO

## Version History

Original |
Introduced |