[Gdal-dev] Spaceview projection

[Frank Warmerdam]

Enrico Zini wrote:
> Hello,
> 
> As part of the effort of geting meteosatlib[1] nearer to gdal, I have to
> handle images using the spaceview projection in GDAL.  Problem is, I
> didn't quote understand how.
> 
> It does not seem to be a simple affine transform.  The formula to go
> from latitude,longitude to projected space that meteosatlib uses is:
> 
> Input: m.lat, m.lon.  Output: p.x, p.y:
> 
>     // sublon is the longitude of the point directly below the satellite
>     // orbitRadius is the radius of the satellite orbit in units of
>     //   earth radius.
>     // EARTH_RPOL is the polar radius of the Earth.
>     // EARTH_1E2 and EARTH_E2 are constants for which I didn't find any
>     //   documentation
> 
>     // Convert to radians
>     double lat = m.lat * M_PI / 180;
>     double lon = (m.lon - sublon) * M_PI / 180;
>     
>     double c_lat;
>     double r1,r2,r3,rn,rl;
>     
>     c_lat = atan( EARTH_1E2 * tan(lat) );
>     rl    = EARTH_RPOL / ( sqrt(1.0 - EARTH_E2 * pow(cos(c_lat), 2.0)) );
>     
>     r1 = orbitRadius - \
>           rl * cos(c_lat) * cos(lon);
>     r2 = -rl * cos(c_lat) * sin(lon);
>     r3 = rl * sin(c_lat);
>     rn = sqrt( r1*r1 + r2*r2 + r3*r3 );
>     
>     p.x = atan(-r2 / r1) * 180 / M_PI;
>     p.y = asin(-r3 / rn) * 180 / M_PI;


Enrico,

I'd guess the above should be a projection method in proj.4.  And the
part below is just the normal application of a geotransform in GDAL.

I vaguely recall someone offering a meteosat projection for PROJ.4 in
the past, and I think I sent him on to Gerald.  I don't know what came
of that.

Best regards,

> To get to the pixel coordinates in the image, a simple extra scaling
> step is required, taking as input the pixel resolution and the offset of
> the top left pixel:
> 
>     x = (int)rint((double)p.x * column_resolution) + image_xstart;
>     y = (int)rint((double)p.y * line_resolution) + image_ystart;
> 
> 
> Is there anything like this in GDAL?  If not, how can it be added?


-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org