Re: Curve with arrow.

[<Mick.Spillane@xxxxxxxx>]

Hi Jian,
	This may not be exactly the answer to your question either,
but may be of use to you or others in some situations.

	Suppose you want to annotate (label) a plot with a symbol
that suggests rotation, then you may be able to combine certain
"characters" from the @EL (electrical) and @MP (map) symbol fonts
(with the ^ that achieves superscript.)

Try the following demo:

plot/vs/nolab {0,1},{0,1} ! just something to draw on
label/nouser 1 1 0 0 0.5 @el15^@mp14      ! the black curved arrow
label/nouser 1 4 0 0 1.0 @p2@el15^@mp14   ! the red one
label/nouser 6 4 0 270 1.0 @p3^@mp12@el18 ! the green one
label/nouser 6 2 0 135 1.0 @pg@el15^@mp14 ! the thick blue one

There are two basic arrows shown here
        counterclockwise : ^@mp12@el18
               clockwise : @el15^@mp14

but notice that you can change the orientation, size, color, and
thickness by changing the various arguments of the label command
and the pen (@p1 to @pg).
Also, if you drop the "/nouser" the x and y coordinates will be
in terms of the scales of the plot axes rather than the inches of
the above demo.

One other point that might be of use to someone.  If you create
the underlying plot with "/nolab/set_up" you can make the arrow
labels as movable Plotplus labels that can be positioned with
the aid of crosshairs. Try this demo - when you type the
"ppl plot" command the plot is drawn then for each label you
have defined a crosshair and selection box appears.  First
click on the selection box choice you wish - generally center,
then click again in the place you want the symbol to appear.

plot/vs/nolab/set {0,1},{0,1}
ppl hlabs,1,0.5 ; ppl rlabs,1,60 ; ppl labs,1,@pd@el15^@mp14
ppl hlabs,2,0.7 ; ppl rlabs,2,200 ; ppl labs,2,@pd^@mp12@el18
ppl plot

Here you need to use "ppl hlabs" and "ppl rlabs" to change the
size and orientation of the symbol and the placement of the
symbol in relation to the crosshair may require some
experimentation.  Ferret/Plotplus will write the coordinates
of the symbol to a file called fort.41 which you can edit to
make the symbol always appear in the same place in future
plots without interaction (or you could modify the position
slightly.)

Good Luck,
Mick
PS: While you have the movable label demo going, try the "arrow"
and "line" options in selection box to see effects that may be of
use in other contexts.  You will need to click twice (instead of
once) more per label to draw an arrow/line from a point of
interest to the label itself.

|!!! Mick.Spillane@noaa.gov !!!|
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