Re: plane rotation

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Hi all,
After an off-line conversation with Ned Cokelet of our lab, the question 
comes down to defining different kinds of axes.  They do not need to be 
rectangular latitude-longitude axes. Because the rotated grid has 
different values of longitude along a grid line, and likewise for 
latitude, it will need to be expressed as a "curvilinear" grid.

So, you can define the new grid using cos and sin relationships.  If all 
you need is graphical output, you can use the ideas from the map 
projection scripts  (like mp_mercator.jnl etc) to define the coordinates 
for the rotated grid, and then use the curvilinear plotting capabilities 
of Ferret. You need to create two new variables, one with the longitudes 
at each grid point of the new 2-D grid, and one with the latitudes, also 
in 2 dimensions.

This would be along these lines, if your variables is called VAR.

  let xpts = x[gx=var]
  let ypts = y[gy=var]
  let angle_deg = 30.
 
  let Pi = 3.14159265
  let deg2rad = Pi / 180.0
 
  let angle_rad = angle_deg* deg2rad
  let xrad = xpts * deg2rad
  let yrad = ypts * deg2rad
 
  let xcoord = xrad* cos(angle_rad) - yrad* sin(angle_rad)
  let ycoord = yrad* cos(angle_rad) + xrad* sin(angle_rad)
 
  shade/noaxes var, xcoord, ycoord


If you need to do computations with the data on the new grid, you could 
use the RECT_TO_CURV regridding function which was released with Ferret 
version 5.8, and regrid var onto the curvilinear grid defined by xcoord 
and ycoord.

(I'll incorporate the above into a new map projection script, 
mp_rotate.jnl for future releases.)

Ansley

Hemerson Tonin wrote:

> Hi Ferreters,
>
> Has anybody out there a good idea to define axis (and grid) to be 
> inclined ?
>
> I would like to rotate my grid on XY plane, and my "new X-axis" must 
> have an angle in relation to Equator.
>
>
>
> original  (XY 
> plane)                                                            I 
> need (XY plane)
>
>                                                                                                             
> / <-- "new X -axis"
>                                                                                                            
> /
> -----------> Equator and "current X - axis" 
> ---------/---------------------------- Equator
>
>
>
> Hemerson Tonin
> School of Chemistry, Physics and Earth Sciences
> Flinders University
> Adelaide - Australia