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Re: ENVI Navigating GeoTiff Image Incorrectly? [message #78200 is a reply to message #78116]

Fri, 28 October 2011 07:20

guillermo.castilla.ca is currently offline

guillermo.castilla.ca
Messages: 27
Registered: September 2008

Junior Member

Hi David,

I think the problem could be that your tiff image does not use the
upper left corner of the tie point pixel as the reference. To make
sure that pixel coordinates refer to the center of the pixel as in the
ENVI convention, I do the following (assuming there is no rotation):

ok = QUERY_TIFF(myTiff, imginfo, GEOTIFF= mapinfo)
psz=mapinfo.ModelPixelSCALETAG[0] ; pixel size
x0= mapinfo.ModelTiePointTag[3] - mapinfo.ModelTiePointTag[0]*psz
y0= mapinfo.ModelTiePointTag[4] + mapinfo.ModelTiePointTag[1]*psz

ModelTiePointTag[0:1] indicate whether the coordinates of the tie
point refer to:
(1)the upper left corner of the pixel
(and in this case ModelTiePointTag[0:1]=[0,0]);
(2) the center of the pixel (ModelTiePointTag[0:1]=[0.5,0.5]); or
(3) the lower left corner of the pixel
(ModelTiePointTag[0:1]=[0,0.5])

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.

Cheers

Guillermo

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[Message index]

		Re: ENVI Navigating GeoTiff Image Incorrectly? By: David Fanning on Thu, 27 October 2011 07:43
		Re: ENVI Navigating GeoTiff Image Incorrectly? By: devin.white on Thu, 27 October 2011 02:44
		Re: ENVI Navigating GeoTiff Image Incorrectly? By: David Fanning on Wed, 26 October 2011 14:33
		Re: ENVI Navigating GeoTiff Image Incorrectly? By: guillermo.castilla.ca on Fri, 28 October 2011 07:20

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