[Gdal-dev] Almost got it - I'm learning.

Ed McNierney ed at topozone.com
Sat Sep 11 09:14:32 EDT 2004

Sean -

Go to TerraServer, where you will find documentation on how to construct
the URL request you're using.  Their assumption is that you know the UTM
coordinates and need to convert that to URL querystring parameters, but
it's a very simple transformation and you can calculate the reverse.  If
you know  the TerraServer image-fetch querystring, you DO know the UTM

	- Ed

-----Original Message-----
From: gdal-dev-bounces at xserve.flids.com
[mailto:gdal-dev-bounces at xserve.flids.com] On Behalf Of S Clark
Sent: Friday, September 10, 2004 11:50 PM
To: gdal-dev at xserve.flids.com
Subject: [Gdal-dev] Almost got it - I'm learning.

OKAY - several facts are falling into place in my ignorant brain now.
(It's like an intellectual trepanning - a hole has been poked in my mind
to let the ignorance out...)

1.)UTM coordinates aren't latitude/longitude degrees.  (And everyone
else on the list, who probably knows what they are doing, are now
slapping their heads and saying "duh"...)

2.)I cannot provide the 'world file' information as part of the command
line (didn't realize that.  No problem, I dug up the format of the world
file and can generate one, once I know how to calculate the facts that I
need to put in it from the facts that I have...)

3.)I need to figure out how to calculate "easting" and "northing"
for a particular UTM zone (I already know how to calculate which zone I
am in.)

Seems like the only thing left that I need to figure out is how to
calculate the "easting" and "northing" of the upper-left pixel of the
map from the latitude and longitude degrees of the map center and the
"scale" (or meters/pixel, which I can derive from the "scale").

I'll see if I can get that figured out tonight.  If all goes well,
sometime in the next day or so I'll be back to post "Whee!
I've got it!"...

Thanks once more


On Friday 10 September 2004 09:00 pm, you wrote:
> Sean -
> Read my last message about missing info for the source image.  Stop 
> adding parameters to the -s_srs object; you're confusing the 
> properties of the data set (the image) with the properties of the 
> projection.  For the UTM projection as your s_srs, zone= and datum= 
> should be the only properties you need.
> Your UTM map will not have a center point (or upper-left point) with 
> coordinates expressed in degrees, as the units for that projection are

> meters, not degrees.  That's fine - you'll create that in the world 
> file and gdalwarp will take care of the rest.
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