[Gdal-dev] saving GeoTiff

[Ayman Kamal]

1.
sorry sir if I was wrong when calling "NAD83",.. 
coordinate systems, but I referred to 
http://gdal.velocet.ca/projects/opengis/ogrhtml/osr_tutorial.html

where it mentions exactly:
"The OGRSpatialReference has built in support for a
few well known coordinate systems, which include
"NAD27", "NAD83", "WGS72" and "WGS84....."


2. I changed the pixel size by changing the values of
adfGeoTransform[1]//horizental pixel size
adfGeoTransform[5]//vertical pixel size

in "gdal_translate" code.

I am sure that the pixel size was changed, as I opened
the images in other softwares and noticed that the
size of the grid cells has changed accordingly.

3. Anyway, what I want simply is as follows:
I want to show a dialog the user that contains the
parametes he/she must fill to be able to generate a
correct GeoTiff image,
-I figuered out that I will ask him/her to choose one
of "NAD83","NAD27","WGS72","WGS84"
-Ask him/her about the latitude and longitude of top
left corner
-Ask him/her about pixel size, and I mention the unit
of size, so what does DATUM mean, and if he chooses
any of the DATUMs, what will the unit be?


--- Ed McNierney <ed at topozone.com> wrote:
> Ayman -
> 
> 1. The four mentioned "coordinate systems" are
> datums, not coordinate
> systems.  The "units of the model system" depend
> upon the specific map
> projection you are using.  For example, I live in
> Masschusetts, USA, and
> locally we use the Massachusetts State Plane
> coordinate system, which
> can be implemented in either feet or meters.  The
> majority of projected
> coordinate systems use meters, but the correct value
> will depend on the
> specific system you are using.
> 
> 2. The top left corner coordinates and pixel size
> are all floating-point
> numbers and can accommodate any plausible numbers
> you might have.
> 
> 3. I don't think you have given us enough
> information here - can you
> explain exactly how you changed the pixel size?
> 
> 	- 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 10:03 AM
> To: gdal-dev at remotesensing.org
> Subject: Re: [Gdal-dev] saving GeoTiff
> 
> ok sir, I figured out that the pixel size decides
> how
> long does the pixel represent in actual model system
> units, as the scale factor for geograpich maps,
> 
> 1. Now I just want to know, for the 4 mentioned
> coordinate systems
> "NAD27", "NAD83", "WGS72", "WGS84" what are the
> units
> of the model system?? I want to ask the user to
> explain this for the user.
> 
> 2. What are the ranges for valid data the user can
> provide for the top left corner of image & for pixel
> size.
> 
> 3. I saved a certain image using GDAL and each time
> changed the pixel size,and then opened this image
> using GDAL and noticed that there was no difference
> in
> how the image looked like, I am sure of that. Can
> you
> explain?
> 
> 
> --- Frank Warmerdam <warmerdam at pobox.com> wrote:
> > Ayman Kamal wrote:
> > > Then, if it can be derived, how can I do so, If
> it
> > > can't, can you give me more explanation?
> > > 
> > > If you don't have enough time to answer me, can
> > you
> > > please givem me a link to a web page or
> whatsoever
> > > resource that explains this. I need to
> understand
> > this
> > > point THOROUGHLY.
> > 
> > Ayman,
> > 
> > I do not know off hand of a resouce that discusses
> > this thoroughly.  I would
> > suggest you review the information in the GDAL
> data
> > model document about
> > "Affine GeoTransform".
> > 
> >   
> >
>
http://www.remotesensing.org/gdal/gdal_datamodel.html
> > 
> > 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
> > 
> > 
> > _______________________________________________
> > Gdal-dev mailing list
> > Gdal-dev at remotesensing.org
> > http://remotesensing.org/mailman/listinfo/gdal-dev
> 
> 
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