[Gdal-dev] saving GeoTiff

Thu Mar 20 11:17:35 EST 2003

Ayman -

It seems from your earlier emails that you already have done this and you know the answer to your question.  You have reported that changing only the georeference data in the GeoTIFF does not change the appearance of the BMP file, correct?

You're being a little confusing in saying "the raster data" when it seems that you mean "the BMP file generated by gdal_translate".  There's raster data in the GeoTIFF file, and when you ask "does changing the georeference data modify the raster data", I assume you're talking about the raster data inside the GeoTIFF file.

	- Ed

-----Original Message-----
From: Ayman Kamal [mailto:kamal_jo at yahoo.com]
Sent: Thursday, March 20, 2003 11:06 AM
To: gdal-dev at remotesensing.org
Subject: RE: [Gdal-dev] saving GeoTiff

Sorry, but your answer didn't help me.
What I wanted to know simply is
If I convert a GeoTiff file to a BMP file using
"gdal_translate"

Is the data that I will get in t the resulting BMP
file is just the raster data found in the GeoTiff
file, or does the geotiff data saved in the GeoTiff
file affect how the resulting BMP file will look like?

--- Ed McNierney <ed at topozone.com> wrote:
> Ayman -
> 
> You should ask that question to the developer of the
> viewing program you are using.  It's entirely up to
> that program to decide what data it uses or does not
> use when displaying an image.
> 
> 	- Ed
> 
> -----Original Message-----
> From: Ayman Kamal [mailto:kamal_jo at yahoo.com]
> Sent: Wednesday, March 19, 2003 11:11 AM
> To: gdal-dev at remotesensing.org
> Subject: RE: [Gdal-dev] saving GeoTiff
> 
> 
> 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.
> 
> 
> --- 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
> > > > 
> 
=== message truncated ===

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