# [Proj] Re: To handle geographic info from HDF5 formated Satellite Data

Aydin agerturk at gmail.com
Thu May 8 07:21:14 EDT 2008

```Frank Warmerdam <warmerdam <at> pobox.com> writes:
>
> Aydin,
>
> PROJ.4 does not address transformation from pixel/line space to georeferenced
> space.  Just projected space to geographic space (and back).  The info above
> does not indicate an ellipsoid, but we might assume WGS84 as a guess.
> If the corners are in long/lat ordering we can assume the top left corner
> is 25W, 75N.  This can be converted to equidistant cylindrical coordinates
> like this:
>
> proj +proj=eqc +lat_ts=0 +lon_0=0.000000 +ellps=WGS84
> -25 75
> -2782987.27     8348961.81
>
> So, the top left corner is -2782987.27mE, 8348961.81mN.
>
> Actually, treating this as a projection issue is rather silly since
> the projection is eqc which is just a scaling of geographic space.
> And since all the locations and pixel sizes are expressed in decimal
> degrees you might as well just ignore that aspect, and treat this as
> a WGS84 image with the given corners.
>
> So, if the top left corner is -25,75 and the pixel size is
> 0.560648, 0.56215554 you could compute pixel (20in from left,15 down
> from top) as:
>
> longitude = -25 + 0.560548 * 20
> latitude = 75 - 0.560648 * 15
>
> etc
>
> Best regards,
Frank,

Thank you for response.
if I use your suggestion, for example pixel (1000,1000);

longitude = -25 + 0.560648 * 1000 = 5581.48
latitude = 75 - 0.560648 * 1000 = -5531.48

So, it is not possible.

I do not have problem converting projected space to geographic space using
proj lib. My problem is how can calculate the distance from the corner using
below parameters than I can convert those to lat/lon.

Best Regards,
Aydin

```