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Re: ENVI Navigating GeoTiff Image Incorrectly? [message #78197 is a reply to message #78134]

Fri, 28 October 2011 07:40

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Guillermo writes:

> See if your ModelTiePointTag[0:1]=[0,0]. If not, you were wrongly
> assuming that the geotiff coordinates referred to the upper left
> corner of the tie point pixel. This might not be necessarily be the
> case.

This is useful information, although I don't believe I have
ever encountered a TIFF file in which the tie point didn't
represent the upper-left corner of the tie point pixel.
But I'll be looking more closely from now on!

In any case, the file in question was using this convention,
so there is no mistake there. Aside from the obvious errors
ENVI is making in just the basic TIFF manipulations, the
pixels in the sample feature I was talking about, were located
anywhere from 2 to 200 meters away from where I calculate
they are suppose to be. (200 meters is 1/8 the length of the
entire feature, and the actual different from one pixel to
another is variable, not a simple offset. If it *were* a
simple offset, my confidence in my own code wouldn't be
nearly as strong. I would suspect ENVI was doing something
I didn't understand yet.)

I feel 99.9% confident that ENVI is doing this calculation
incorrectly. This may be a moot point, however, since
ENVI has moved on to ESRI map projection code, and my
client is thinking of upgrading from ENVI 4.5.

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		ENVI Navigating GeoTiff Image Incorrectly? By: David Fanning on Wed, 26 October 2011 14:08
		Re: ENVI Navigating GeoTiff Image Incorrectly? By: David Fanning on Sun, 30 October 2011 10:31
		Re: ENVI Navigating GeoTiff Image Incorrectly? By: David Fanning on Fri, 28 October 2011 07:40
		Re: ENVI Navigating GeoTiff Image Incorrectly? By: guillermo.castilla.ca on Fri, 28 October 2011 07:35

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