|
|
| Re: map_proj_inverse and map_proj_init IDL 6.2 [message #46609 is a reply to message #46603] |
Fri, 02 December 2005 23:02  |
enod
Messages: 41
Registered: November 2004
|
Member |
|
|
As far as I know, map_proj_inverse and map_proj_forward functions are
only supposed to derive the longitude and latitude coordinates from map
projection coordinates, and vice versa. I don't think it can be used to
register an image without projection.
Regards,
Tian
Liberum wrote:
> Hi everyone,
>
> I am sure someone has the answer to this question:
> I am trying to georegister an array using map_proj_inverse and
> map_proj_init in IDL 6.2. Since this is the first time I have done
> this, I have made some mistakes but I got IDL to execute the program
> without error. The problem is that the results look, well, wacky. The
> array is a Meteosat 8 image slice in satellite projection. My function
> looks like this:
> ************************************************************ **************
> FUNCTION xy2deg, data
> x = (size(data,/dimensions))[0]
> y = (size(data,/dimensions))[1]
>
> ; map projection info
> map_info = MAP_PROJ_INIT('satellite',datum=8, $
> SPHERE_RADIUS=6378169.0, $
> HEIGHT=42164000.0,SAT_TILT=0, $
> CENTER_LONGITUDE=0,CENTER_LATITUDE=0, $
> ROTATION=0)
> indices = indgen(2,x*y)
> ind = 0L
> for i=0, y-1 do begin
> for j=0, x-1 do begin
> indices[0,ind] = j
> indices[1,ind] = i
> ind = ind + 1
> endfor
> endfor
> result = MAP_PROJ_INVERSE(indices,MAP_STRUCTURE=map_info)
> return, result
> end
> ************************************************************ **************
> IDL> res = xy2deg(data)
> IDL> print, res(*,500) ; for example
> 0.0044915539 0.0000000
> IDL>
> IDL> print, size(res,/dimensions)
> 2 690000
> ------------------------------------------------------------ ------------------------------------------------------------ -----
> Can anyone give me some tips here? I wonder if I need to know more
> about the region the array covers. I am not 100% sure on the SAT_TILT
> nor the ROTATION but these should not have such a large effect.
>
> Sincerely,
> Sheldon
|
|
|
|
| Re: map_proj_inverse and map_proj_init IDL 6.2 [message #46610 is a reply to message #46609] |
Fri, 02 December 2005 09:08 |
David Streutker
Messages: 34
Registered: June 2005
|
Member |
|
|
Can you explain what you mean by "wacky"? I'm not sure I see anything
wrong.
I think the problem may be your coordinate units. It looks like
MAP_PROJ_INIT and MAP_PROJ_INVERSE convert to degree coords from meter
coords (not data indices). The result you got was converting the
physical location (500 m, 0 m) to lon/lat, and not the pixel at
[500,0].
Essentially, I think you need to include the spatial resolution of
Meteosat somewhere in your code.
-Dave
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
