Re: vector and stereographic map

[Ansley Manke <ansley@xxxxxxxxxxxxx>]

Hi Thomas,
Thomas and I worked on this off-line, and I think that the
data is on a rectangular grid, laid on an area near the
north pole.  When plotted with the north stereographic
map projection, the grid cells are rectangular, so the
vector should look the way they do in Thomas's plot,
not curved around the pole as they would be on a lat-lon
grid.   So, zonal_motion and meridional_motion are
misleading names for the components of the vectors in
the dataset, but what Thomas is seeing is, I believe, correct.

Ansley Manke

Thomas LOUBRIEU wrote:

> Hi,
>
> I would like to plot vectors from the NSIDC lat, lon grid (an irregular
> grid) with a stereograhic map projection.
>
> My dataset contains :
> latitude(i, j), longitude(i, j), zonal_motion(i, j),
> meridional_motion(i, j))
>
> I use :
>
> set region/x=0:360/y=45:90
> go mp_stereographic_north -45 50
> use $1
> let mp_lambda = longitude*deg2rad
> let mp_phi = latitude*deg2rad
> set grid zonal_motion
> can region
>
> vector/over/len=1000/color=black  zonal_motion, meridional_motion,
> x_page, y_page
>
> let mp_lambda = mp_x * deg2rad
> let mp_phi    = mp_y * deg2rad
> set region/x=0:360/y=45:90
> go mp_fland 20
> go mp_graticule 0 360 10 45 90 10
>
> The origin and module of vectors are correctly plotted but the direction
> of vector is wrong.
> If I set the "meriodional_motion" or the "zonal_motion" to 0, I can see
> that the zonal or the meridional componant are plot along the X or the Y
> direction of the screen window instead of following the real zonal or
> meridional axis (shown by the graticule).
>
> I attached one snap shot with a 0-meridional componant.
>
> What can I do to display the correct vector direction ?
>
> Thanks,
>
> Bye,
>
> Thomas.
>
>   ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>  [Image]

--
Ansley Manke  Pacific Marine Environmental Laboratory  Seattle WA  (206)526-6246