[Gdal-dev] saving GeoTiff

[Ayman Kamal]

Please reply to my email, I need an answer ASAP,
is it correct what I mention below?
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> Maybe I misleaded you with my words,
> what I want to know clearly is the answer to this
> question:
> 
> The data saved in the geotiff file (other than
> raster
> data) is data that specifies the coordinate
> location,
> and this can appear clearly in the grid lines of
> long
> and lat that some viewers show,
> 
> BUT this coordinate data, doesn't affect by any
> means
> the raster data or how it is viewed.
> 
> AND what is mentioned in the geotiff specification
> about geo keys and geo data, is about the data that
> is
> saved in the geotiff file which is extracted to show
> the coordinate grids only.
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> 
> --- Ed McNierney <ed at topozone.com> wrote:
> > Ayman -
> > 
> > YOU need to take the time to understand the
> viewing
> > software you are using.  Read the documentation
> and
> > understand what it is supposed to do.  Then, if
> you
> > find your images do not work as you expect, you
> can
> > explain what the problem seems to be.
> > 
> > If you find that an image appears different using
> > two different viewers, first take time to
> understand
> > what those viewers do and how they display images.
> 
> > It is certainly possible that two different
> viewers
> > will display the same image two different ways;
> > that's not surprising at all, and probably has
> > nothing to do with GDAL.
> > 
> > 	- Ed
> > 
> > -----Original Message-----
> > From: Ayman Kamal [mailto:kamal_jo at yahoo.com]
> > Sent: Wednesday, March 19, 2003 10:50 AM
> > To: gdal-dev at remotesensing.org
> > Subject: RE: [Gdal-dev] saving GeoTiff
> > 
> > 
> > Sir,
> > What I want to make sure about is, if I don't care
> > about showing a grid for coordinates(long,lat),
> then
> > If I just take the raster data out of the geotiff
> > file, this will be adequate?
> > 
> > If we say yes for the above question, then if I
> open
> > a
> > geotiff file and just read the raster data, I
> should
> > get the same view I have when opening it using a
> > GeoTiff viewer, 
> > 
> > BUT what I notices when I started search about 
> > 
> > GeoTiff, when opening geotiff files with ordinary
> > image viwers(not supporting geotiff) they showed
> the
> > image differnt from it appears in geotiff viewrs.
> > 
> > Can you PLEASE explain to me?
> > 
> > 
> > --- Ed McNierney <ed at topozone.com> wrote:
> > > Ayman -
> > > 
> > > What do you expect to see?  Many viewers will
> load
> > > an image and display the entire image on the
> > screen,
> > > or display the upper-left portion at 100% zoom -
> > one
> > > pixel on the screen for each input pixel in the
> > > image.  Both of these views are independent of
> the
> > > geographic coordinates or the pixel size, so
> > > changing those values won't change the image. 
> > They
> > > WILL change the coordinate information (for
> things
> > > like the "size and values of grids", so your
> > > description sounds exactly like what I would
> > expect
> > > to see.
> > > 
> > > 	- Ed
> > > 
> > > Ed McNierney
> > > President and Chief Mapmaker
> > > TopoZone.com / Maps a la carte, Inc.
> > > 73 Princeton Street, Suite 305
> > > North Chelmsford, MA  01863
> > > ed at topozone.com
> > > (978) 251-4242 
> > > 
> > > -----Original Message-----
> > > From: Ayman Kamal [mailto:kamal_jo at yahoo.com]
> > > Sent: Wednesday, March 19, 2003 10:34 AM
> > > To: gdal-dev at remotesensing.org
> > > Subject: RE: [Gdal-dev] saving GeoTiff
> > > 
> > > 
> > > Now, after I saved several GeoTiff files using
> > > "gdal_translate" source as a program to modify
> the
> > > settings of Geo data, I don't know what is the
> > value
> > > of the geo data saved???
> > > 
> > > By changing the values of adfGeoTransform[]
> > elemets:
> > > 
> > > *I change the top left corner (longitude,
> > lattitude)
> > > *I change the pixel size
> > > 
> > > and when I open the image using different
> viewers,
> > I
> > > get the same image no matter what the values
> are,
> > > the
> > > only change I see is the size and values of
> grids
> > of
> > > lattitude and longitude lines.
> > > 
> > > But how the imaage looks, or the height data
> that
> > > some
> > > viewers show, are all unchanged.
> > > 
> > > Can you explain to me??
> > > 
> > > --- Ed McNierney <ed at topozone.com> wrote:
> > > > Ayman -
> > > > 
> > > > Since you mention "latitude and longitude", I
> > will
> > > > assume your data is
> > > > unprojected and in decimal degrees.  If so,
> then
> > > the
> > > > "projection" is
> > > > usually called "unprojected" or "geographic" -
> > you
> > > > need the datum and
> > > > the latitude and longitude to define a
> location.
> > > > 
> > > > If your data is in decimal degrees, then the
> > units
> > > > of pixel size are in
> > > > decimal degrees.  The values specified by the
> > user
> > > > should be the size of
> > > > each pixel in degrees of latitude and degrees
> of
> > > > longitude.  It is
> > > > unusual for raster data to be in decimal
> > degrees,
> > > so
> > > > make sure that is
> > > > correct.  Most raster data is projected.
> > > > 
> > > > 	- Ed
> > > > 
> > > > Ed McNierney
> > > > President and Chief Mapmaker
> > > > TopoZone.com / Maps a la carte, Inc.
> > > > 73 Princeton Street, Suite 305
> > > > North Chelmsford, MA  01863
> > > > Phone: (978) 251-4242  Fax: (978) 251-1396
> > > > ed at topozone.com
> > > > 
> > > > 
> > > > -----Original Message-----
> > > > From: Ayman Kamal [mailto:kamal_jo at yahoo.com] 
> > > > Sent: Tuesday, March 18, 2003 10:42 AM
> > > > To: gdal-dev at remotesensing.org
> > > > Subject: RE: [Gdal-dev] saving GeoTiff
> > > > 
> > > > 1.
> 
=== message truncated ===


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