Vector plotting on vertical sections

[john.hunter@xxxxxxxxxxx]

Hello All,

I have a problem plotting current vectors on a vertical section. 
(There is a minor complication in that the model (POM) uses 
sigma-coordinates -- however I calculate the true vertical coordinate in 
Ferret, such that scaling using "shade" or "contour" works fine; so I do 
not think my problem is related to the use of sigma-coordinates.)

For a typical vertical section, the horizontal extent is about 800000
metres and the vertical extent is about 1000 metres, so a vertical
expansion of around 800 is entailed in the plotting.

This is what I do:

1. I use the default aspect ratio (axis length ratio = 0.75)
by calling:

   set window <window number>

2. I plot "shade" or "contour" first

3. I then do a vector overlay using EITHER:

   vector/overlay/aspect=`ydx` .......
     (where ydx ~ 800, but calculated from the exact horizontal and
     vertical extents)

   OR:

   vector/overlay .......

   Both of these produce vectors which point in the correct direction
   relative to the upper and lower boundaries of the model (i.e. the
   surface and sea bed), and so I assume they are correct. The results
   of both these options also appear to be identical. Any other 
   selection of "ydx" in the first of the above options causes the 
   vectors to point in what is clearly the wrong direction.

   HOWEVER in both of the above ("correct") options the arrow heads
   appear to have been distorted by the vertical expansion, to form
   vertical lines (like "hammer heads" on the end of each vector)
   -- it appears as if the vectors AND their arrow heads have been
   "drawn" on a 1:1 vertical:horizontal scaling, and THEN the whole
   plot has been expanded in the vertical by a factor of ~800.

How do I fix this? I am sure I have seen Ferret plots of vertical
sections where this works O.K., so I am sure there is a simple
solution.

Cheers,

John

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+ John Hunter,                                Tel. (work) 03 6226 7849 +
+ Antarctic Climate & Ecosystems              Tel. (home) 03 6234 8391 +
+ Cooperative Research Centre,                Mobile      0427 098 831 +
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+ Private Bag 80,                 email (work) john.hunter@utas.edu.au +
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