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Re: How to extract pixel values from a GeoTIFF using an Esri Shapefile [message #74179 is a reply to message #74092]

Mon, 03 January 2011 16:25

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Guillermo writes:

> ; populate the mask (assumes is in the same projection
> ;and covers the same extent as the geotiff)
> myshape->IDLffShape::GetProperty, N_ENTITIES=n
> FOR i=0L, n-1 DO BEGIN
> feati= myshape->IDLffShape::GetEntity(i)
> featix= Round((Reform((*feati.vertices)[0,*])-x0)/psz)
> featiy= Round((y0-Reform((*feati.vertices)[1,*]))/psz)
> featis= POLYFILLV(featix, featiy, ns, nl)
> IF featis[0] NE -1 THEN mask[featis]= feati.ishape +1
> ENDFOR

This is nearly identical to the solution I sent Paul
earlier today. The problem with IDLanROI is that it
can't be used in the native projected meter coordinates
that the image and shape files are in. The projected
meter coordinates have to be "converted" to "pixel"
coordinates by subtracting the offset and dividing
by the image range, before they can be loaded in the
object.

I didn't round my values, and I don't think you need
to do so here, even with PolyFillV. In fact, I think
you might get slightly more accurate values by not
rounding, although this is a quibble with Paul's
image.

I've made myself a note to write an article when
I get some time. :-)

Cheers,

David

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

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[Message index]

		How to extract pixel values from a GeoTIFF using an Esri Shapefile By: Paul Magdon on Thu, 23 December 2010 12:53
		Re: How to extract pixel values from a GeoTIFF using an Esri Shapefile By: David Fanning on Mon, 03 January 2011 16:25
		Re: How to extract pixel values from a GeoTIFF using an Esri Shapefile By: Adam Erickson on Wed, 19 August 2015 14:57
		Re: How to extract pixel values from a GeoTIFF using an Esri Shapefile By: guillermo.castilla.ca on Mon, 03 January 2011 14:46
		Re: How to extract pixel values from a GeoTIFF using an Esri Shapefile By: David Fanning on Mon, 03 January 2011 05:55
		Re: How to extract pixel values from a GeoTIFF using an Esri Shapefile By: ittai9 on Fri, 29 April 2016 06:36

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