Vector aspect ratio with poly_vectors

["Gustafson, William I" <william.gustafson@xxxxxxx>]

Dear Ferreters,

This is a two part e-mail dealing with getting the proper aspect ratio when using the poly_vectors script and then a possible bug.

Part 1:
I am trying to write a generalized script that will plot wind vectors for a time-height cross section. I would like the plot window to be tall and narrow and this creates distorted looking vectors if I use the vector command (the hammer heads discussed recently). So, I would like to use the poly_vectors script. If I understand what is happening, I have to apply aspect corrections to my u and v wind components to properly account for the unit difference between the time and height axes as well as the viewport, margin, and window settings. I think the result looks close if I use the script below. However, the aspect correction may be a little off. Can anybody offer a better way to handle this? Exact definitions to all the relevant axis and window symbols would be helpful too?

Here is the relevant part of the script:

set window/size=0.7/aspect=2
contour/set/nolab/color=white/lev=(-1000)/transpose/vlim=($vlims)/d=3 uobs,tobs,hobs
go margins 0.1 1.5 1.3 0.2
ppl xlab "Hours after ($day)-($monthstr)-2000 12Z"
ppl ylab "height (km)"
ppl labset ,0.18,0.18
ppl contour
let aspadj = `($ppl$xlen)/($ppl$ylen)`
let xadj = `(($ppl$xmax)-($ppl$xmin))`
let yadj = `(($ppl$ymax)-($ppl$ymin))*aspadj`
go poly_vectors tobs hobs uobs*xadj vobs*yadj 30 "arrow"
let colval=ysequence(uobssub[d=3])
polygon/over/nolabel/nokey/pal=green plt_x_arrow, plt_y_arrow, colval

Part 2:
Using a script similar to above, if I set ubos=2 and vobs=2 I get a 45 degree vector like I want. And, if I set uobs=2 and vobs=0, I get horizontal vectors, again like I want. However, if I set uobs=0 and vobs=2, the vectors get extremely small. So, either I have totally misunderstood how to set the aspect ratio in part 1 above, or there might be a bug in the poly_vector script. 

Thanks for any suggestions.

-Bill


_______________________________________
William I. Gustafson Jr., Ph.D.
Pacific Northwest National Laboratory
P.O. Box 999, MSIN K9-30
Richland, WA 99352, USA
Voice & Msg: (509)372-6110
FAX: (509)372-6168
http://www.pnl.gov/atmos_sciences