.help velvect Sep85 plot
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NAME
velvect -- two dimensional velocity field plot
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USAGE
velvect uimage vimage
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PARAMETERS
.ls uimage
Name of image containing u components of the velocity field.
.le
.ls vimage 
Name of image containing v components of the velocity field.
.le
.ls device = stdgraph
Output device for plot.
.le
.ls title = "imtitle"
Title to be centered over the plot.  By default, it will be the title
from the image header of the \fBuimage\fR.
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.ls append = no
Append to an old plot?
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.ls verbose = yes
Print warning messages?
.le
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DESCRIPTION
Task \fIvelvect\fR draws a representation of a two-dimensional velocity
field by drawing arrows from each data location.  The length of the arrow
is proportional to the strength of the field at that location and the direction
of the arrow indicates the direction of the flow at that location.  The
two images \fIuimage\fR and \fIvimage\fR contain the velocity field to be
plotted.  The vector at the point (i,j) has:

.nf
    magnitude = sqrt (uimage(i,j)**2 + vimage(i,j)**2)
    direction = atan2 (vimage(i,j), uimage(i,j))
.fi
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EXAMPLES
1. Make a vector plot from the two images "crab.blue" and "crab.red".

    cl> velvect crab.blue crab.red
.endhelp