Re: [ferret_users] Projected data

["Ingo Bethke (uib)" <Ingo.Bethke@xxxxxxxxxxxxxx>]

Hi,

If you are not happy with the default result of the 3-argument versions 
of the SHADE, FILL , and CONTOUR commands you can try the POLYGON 
command in combination with the in ferret available map projections.

I have tested this on curvlinear model output where the cell-corners can 
be used directly to define the polygons. However, it shouldn't be to 
difficult to define pseudo-cells (I guess that is exactly what is done 
in the SHADE command) which suit your data. The attached figures crudely 
illustrate how the result from the curvlinear output looks like.

Following steps are involved:
The polygon-coordinates need to be gathered in longitude and a latitude 
matrices where the first dimension corresponds to the number of points 
in each polygon and the second to your data dimension. It might be 
neccessary to check and fix the longitude information of each polygon 
(e.g.  179 and -179 -> 179 and 181 ect.).  After calling the projection 
script (e.g. go mp_orthographic 0 90) you need to set the variabels mp_x 
and mp_y to your polygon longitude and latitude coordinates. Prior to 
the call of the 3-argument version of the polygon command (e.g. polygon 
x_page*mp_mask,y_page*mp_mask,sst) you might also want to call mp_aspect.

The drawback of this method is that not all projection scripts are 
robust to user-defined mp_x,mp_y variables. With the exception of 
mp_orthographic I'm still trying hard to get grid lines and land masks 
right for the different projections.

Hope this helps...

Cheers, Ingo



Ansley Manke wrote:

> Hi Tony,
> You can plot this data with the curvilinear forms of the plotting 
> commands.  The variables LONGITUDE and LATITUDE are 2-dimensional 
> curvilinear coordinate fields, so you can use this command to get the 
> correct longitude and latitude labellings
>
> fill temperature, longitude, latitude
>
> The fact that the SHOW GRID has the axes of the variables like 
> temperature labeled as longitude and latitude is misleading; the axes 
> are just indices 1 to 792 and the coordinates are in the curvilinear 
> coordinate variables.   Look at the SHOW GRID output:
>
> yes? show grid temperature
>    GRID GPI1
> name       axis              # pts   start                end
> X         LONGITUDE          792 r   1E                   72E(792)
> Y         LATITUDE           792 r   1N                   792N
> ...
>
> It has a latitude 1 N to 792N, and longitude 1 to 792 as well, which 
> is clearly incorrect.  The curvilinear graphics commands require that 
> the X and Y axes of the variable field such as TEMPERATURE or 
> SALINITY, and the X and Y axes of the coordinates LONGITUDE and 
> LATITUDE agree and then it can draw the plot.
>
> Ansley
>
>
> Tony Jolibois wrote:
>
> >           Hi all,
> >
> > I have to plot some stereographic projected data (latitude 55N to 
> > 90N, projected in the netCDF), and I don't know how I can use it with 
> > longitude and latitude (instead of x and y).
> >
> > Here is the ferret command I use to produce the plot attached. The 
> > axes are not good and I can not fill the land mask...
> >
> > [console@rdp1-jaune arc]$ ferret -nojnl
> >         NOAA/PMEL TMAP
> >         FERRET v5.50
> >         Linux 2.4.3-12smp - 01/15/03
> >         12-Oct-05 09:40
> >  
> > yes? use mercatorPsy3v1R1v_arc_mean_20050923_R20051005.nc
> > yes? show data
> >      currently SET data sets:
> >     1> ./mercatorPsy3v1R1v_arc_mean_20050923_R20051005.nc  (default)
> >  name     title                             I         J         
> > K         L
> >  TEMPERATURE
> >           temperature                      1:792     1:792     
> > 1:43      ...
> >  SALINITY salinity                         1:792     1:792     
> > 1:43      ...
> >  U        zonal velocity                   1:792     1:792     
> > 1:43      ...
> >  V        meridian velocity                1:792     1:792     
> > 1:43      ...
> >  KZ       vertical eddy diffusivity        1:792     1:792     
> > 1:43      ...
> >  LONGITUDE
> >           longitude                        1:792     1:792     
> > ...       ...
> >  LATITUDE latitude                         1:792     1:792     
> > ...       ...
> >  SSH      sea surface height               1:792     1:792     
> > ...       ...
> >  MLD      temperature ocean mixed layer t  1:792     1:792     
> > ...       ...
> >  MLP      density ocean mixed layer thick  1:792     1:792     
> > ...       ...
> >  TAUX     windstress eastward Tx componen  1:792     1:792     
> > ...       ...
> >  TAUY     windstress northward Ty compone  1:792     1:792     
> > ...       ...
> >  QTOT     total net heat flux              1:792     1:792     
> > ...       ...
> >  EMP      water flux                       1:792     1:792     
> > ...       ...
> >  QSR      surface downward solar heat flu  1:792     1:792     
> > ...       ...
> >  
> > yes? show grid temperature
> >     GRID GPI1
> >  name       axis              # pts   start                end
> >  X         LONGITUDE          792 r   1E                   72E(792)
> >  Y         LATITUDE           792 r   1N                   792N
> >  DEPTH     DEPTH (m)           43 i-  0                    5500
> >  normal    T
> > yes? set region/x=1:792/y=1:792/z=0
> > yes? fill/levels=(-3,15,0.2) temperature
> >
> > Best regards,
> > Tony
> >
> > --
> > Tony Jolibois
> >
> > CLS - Direction Océanographie Spatiale
> > 8-10 rue hermès - 31520 Ramonville Saint-Agne
> > tjolibois@cls.fr
> >
> > Tél : +33 (0) 561 393 797
> > Fax : +33 (0) 561 393 782
> >  
> >
> > ------------------------------------------------------------------------