Re: Vectors with sigma coordinate

[Jonathan Callahan <callahan@xxxxxxxxxxxxx>]

Srdjan,

The three-argument vector command for "curvilinear coordinates" is not
yet robust.  As you discovered, the vector lengths are not perfect.  We
included the three-argument vector command in the  release so that
people could get a qualitative feel for their vector data. 
Quantitatively, the vectors have the correct lengths relative to each
other, but don't match the length given in the legend.

To see your vectors at some reasonable length, I'd suggest you simply
use the /LENGTH=## qualifier for the vector command.  For
non-curvilinear coordinates, this somewhat counterintuitive qualifier
associates a length of 1/2 inch with a speed of ##.  For the curvilinear
coordinates, the vector length won't be 1/2 inch and I can't say exactly
what it will be so you'll have to play with it.

Good luck,

-- Jonathan Callahan


"S. Dobricic" wrote:
> 
> Hello,
> 
> When I use the three-argument vector command to plot velocity on a sigma
> coordinate vertical section all vectors are so big that they go out of
> the window.  Other plotting commands (shade, fill and contour) work very
> well. Does anybody know how to solve this problem?
> 
> To scale the vertical coordinate I use a 3D array with heights of data
> points. In my case vectors should not be rotated, because they are
> formed from horizontal and vertical components of the velocity, but only
> positioned according to their height. If vectors are rotated in the new
> projection by ferret, it could be helpful to know how is it done. I
> could not find this information in the documentation.
> 
> Thanks.
> 
> I used following commands (u and w are 3D velocity components fields,
> and lyr_hgt is the 3D matrix with heights of data points):
> 
> set data test.cdf
> define grid/x=lon/y=lat/z=level/t=time gg
> let ygg = y[g=gg]
> set variable/title="Latitude"/unit=degrees_north ygg
> fill w[x=15,l=20], ygg, lyr_hgt[x=15]
> contour/overlay w[x=15,l=20], ygg, lyr_hgt[x=15]
> !!!! The next command gives the wrong plot:
> vector/overlay v[x=15,l=20],w[x=15,l=20], ygg, lyr_hgt[x=15]
> 
> --
> Srdjan Dobricic, Joint Research Centre SAI-MEU (TP-690)
> Via E.Fermi 1,I-21020 Ispra(Va),Italy
> srdan.dobricic@jrc.it,tel:+39-0332-785232,fax:+39-0332-789648