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

S Clark smc+gdal at dogphilosophy.net
Fri Sep 10 23:50:00 EDT 2004

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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