[Gdal-dev] saving GeoTiff

[Ayman Kamal]

Thank you very much sir, 
but still I have one point not clear enough: "pixel
sie", I want to ask the user to supply me with the
needed data, Shall I put in the dialog "pixel size"

please I need to understand this point correctly.

By the way, I figured out that there are vertical
DATUMs like NAVD, are they supported in GDAL?


--- Frank Warmerdam <warmerdam at pobox.com> wrote:
> Ayman Kamal wrote:
> > 1.
> > You mentioned that
> > adfGeoTransform[0] =   /* top left x */
> > adfGeoTransform[3] =   /* top left y */
> > 
> > -Does top left x mean the value of longitude for
> top
> > left corner?
> > -Does top left y mean the value of lattitude for
> top
> > left corner?
> 
> Ayman,
> 
> Yes, if the coordinate system of the image is
> lat/long.
> 
> > 2.
> > What does horizental, vertical pixel size mean?
> 
> The width of a pixel is the coordinate system being
> used.
> 
> > 3.
> > Are adfGeoTransform[2],adfGeoTransform[4] always
> 0?
> 
> No. If the image is not "north up", that is the
> image is
> rotated or sheared from the normal map orientation
> these will
> be non-zero and then the interpretation of the pixel
> size is
> more complicated.
> 
> In common use these values will be zero.
> 
> > 4.
> > If the user doesn't give me any of these data, and
> > still wants me to generate a GeoTiff file out of
> his
> > faces' images for example, 
> > are there default values that I can supply to
> generate
> > a valid GeoTiff file?
> 
> It is pointless to create a "Geo" TIFF file without
> knowing anything
> about a meaningful coordinate system.  If you feel
> the need to do so pick
> any random values you feel like.
> 
> Best regards,
> -- 
>
---------------------------------------+--------------------------------------
> 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    | Geospatial
> Programmer for Rent
> 
> 
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