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Re: [ferret_users] Re: Remapping curvilinear coordinates to rectilinear coordinates

I need to use (I think I need to) the function CURV_TO_RECT_MAP and CURV_TO_RECT (I want to transform wind data from one bigger curvulinear grid to another smaller rectilinear and next use it in a model)
there is a tutorial on the internet:

yes? ! For convenience define variables with the input grid 

yes? let lonin = geolon[d=1]
yes? let latin = geolat[d=1]

yes? ! Define output grid and a variable on the output grid 

yes? define axis/x=0:360:5/modulo/units=degrees xax
yes? def axis/y=0:85:5/units=degrees yax
yes? let lonlatout = y[gy=yax] + x[gx=xax]

yes? ! Compute the mapping to the rectangular grid, save to a file
yes? let map = curv_to_rect_map ( lonin,latin,lonlatout,10)
yes? save/clobber/file=curv_map.nc  map

so what I need it's a properly lonlatout matrix which I would like to cover the following area:

(bottom left) -5.67E, -2S (bottom right) 5.25W, -2S
(top left) -5.67E, 10N (top right) 5.25W, 10N

So I need one matrix and I don't excatly know how to get it. e.g. in matlab one may get matrices X and Y but curv_to_rect_map  demand only one.

2010/10/8 Karl Smith <Karl.Smith@xxxxxxxx>
Hi Simon,

This defined a grid which can be used as the grid for other data.  If you want the equivalent of meshgrid as you mentioned in your later e-mail,

set grid grid_out
def xvals = X + 0.0 * Y
def yvals = 0.0 * X + Y

The xvals and yvals are then variables that can be saved or used as desired.

-- Karl

On 10/8/2010 9:15 AM, Szymon Roziewski wrote:
Hi Karl,
Thank You for your response,
I tried as You told me and what happened next:

 **ERROR: variable unknown or not in data set: GRID_OUT
LIST/FORMAT=CDF/format=(448F8.2)/file=GRIDOUT/clobber grid_out
Command file, command group, or REPEAT execution aborted

ferret doesn't know about values on this grid maybe because treats this
as an abstract object.

2010/10/8 Karl Smith <Karl.Smith@xxxxxxxx <mailto:Karl.Smith@xxxxxxxx>>

   Hi Simon,

   Using the E/W on the X axis and N/S on the Y axis will identify them
   as longitude/latitude.  So you were close.

   -- Karl

   define axis /x=5.666666667E:5.25W:0.083333333 xax
   def axis /y=2.0S:10.0N:0.083333333 yax
   def grid /x=xax /y=yax grid_out

   On 10/8/2010 7:54 AM, Szymon Roziewski wrote:

       Now I'm thinking how to make appropriate grid for that:

       My data are on grid;

       (bottom left) -5.67E, -2S (bottom right) 5.25W, -2S
       (top left) -5.67E, 10N (top right) 5.25W, 10N

       Maybe there is special function wchich dealing with it in ferret?

       2010/10/8 Szymon Roziewski <szymon.roziewski@xxxxxxxxx

           I found it,
           the problem was about statement:

           let grid_out = y[gy=yax] + x[gx=xax]
           which I didn't get well.


           2010/10/8 Szymon Roziewski <szymon.roziewski@xxxxxxxxx

               I also attach my script which does compute coefficient

               DEFINE AXIS/x=1:448:1/unit=degree xaxis
               DEFINE AXIS/y=1:615:1/unit=degree yaxis
               DEFINE GRID/x=xaxis/y=yaxis gridlonlat
               !read curvilinear coordinates onto grid 448x615
               !create grid which we desire
       axis/x=-5.666666667:5.25:0.083333333/modulo/units=degrees xax
               def axis/y=-2.0:10.0:0.083333333/units=degrees yax
               let grid_out = y[gy=yax] + x[gx=xax]
               !do transformation matrix
               let map = CURV_TO_RECT_MAP(clon_in[d=1], clat_in[d=2],
       grid_out, 4)
               !save data
               save/clobber/file=curv_map_UM_TO_ICM.nc map

               and another script which uses it:

               DEFINE AXIS/x=1:448:1/unit=degree xaxis
               DEFINE AXIS/y=1:615:1/unit=degree yaxis
               DEFINE GRID/x=xaxis/y=yaxis gridlonlat
               !load data for transformation  - wind fields u,v
               !using transform matrix
               use "/home/szymon/ferret/vectors/curv_map_UM_TO_ICM.nc"
               ! do transformation
               let wlon_icm = curv_to_rect(wlon[d=1], map[d=3])
               let wlat_icm = curv_to_rect(wlat[d=2], map[d=3])
               !save transformation data which You can see for example
       in the

         *wind_2010092103_ICM_remapped_132x145_and_interpolated.gif* or
               (vectors only)*

               Best regards,

               2010/10/8 Szymon Roziewski <szymon.roziewski@xxxxxxxxx

                   Hello there,
                   I have problem with appropriate remapping from
                   coordinates to rectilinear coordinates.
                   The area which is covered with curvilinear
       coordinates is
                   bigger than I need in rectilinear coordinates (it's
       a subset
                   of curvilinear grid).
                   I would like to raise such a question if ferret can
       do this
                   transformation automaticly i.e. I needn't to care
       about the
                   curvilinear grid is about bigger area than rectilinear.
                   Or I need to tell ferret that fact by some
       computations and
                   I attach files:
                   - wind_2010092103_ICM_aspect.gif - this is wind on
                   curvilinear grid it is a bigger area
       wind_2010092103_ICM_remaped_132x145_and_interpolated.gif -
                   this is wind on rectilinear grid it's a smaller area.

                   As You can see ferret did transformation but in a way I
                   didn't intend. The Baltic Sea area is a little bit
                   translated to the north and the northern part of sea was
                   cut. The picture should wrap all area of Baltic Sea.
                   In the picture

                   I marked the area which matches interpolated wind
       field on
                   Baltic Sea and You can see that it disagrees to
                   wave height which occupies properly area. It means that
                   interpolation from curvilinear grid 448x615 to the
                   rectilinear grid 132x145 was done improperly.
                   I hope I was understood.

                   Kind regards,
                   Szymon Roziewski

Karl M. Smith, Ph.D.
Research Scientist and Software Developer
(206) 526-4806

"The contents of this message are mine personally and do
not necessarily reflect any position of the Government
or the National Oceanic and Atmospheric Administration."

Z wyrazami szacunku,
Szymon Roziewski

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