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How to extract pixel values from a GeoTIFF using an Esri Shapefile [message #74092]

Thu, 23 December 2010 12:53

Paul Magdon
Messages: 8
Registered: January 2011

Junior Member

Dear all,
currently I am developing an pure IDL (No ENVI functions) based remote
sensing application which involves supervised classification.
Therefore I need to import a Geotiff with the raster data plus an ESRI
shapefile (Polygons) with the trainings-data. I then converted the
shape file to an IDLanROI object and build a mask using
IDLanROI::ComputeMask method. At this point I got stuck as I don't
know how spatially link both image and roi even when they are in UTM
projection.

Here is my code so far:
;Import Multispectral Geo TIFF
img=READ_TIFF('some_multispectral.tiff',GEOTIFF=geokeys,inte rleave=2,)
s= SIZE (img, /DIMENSIONS)

;Setup Map projection based on GeoTIFF tags (UTM 17N, Wgs84)
mapCoord = GeoCoord(img(*,*,1),geokeys)
mapStruct = mapCoord -> GetMapStructure()

;import shapfile (aggain UTM 17N, Wgs84)
myshape=OBJ_NEW('IDLffShape', 'some_esri_multipolygone.shp')

;Get the first polygon
ent=myshape->IDLffShape::GetEntity(1)

;Convert SHP to ROI object
myroi = OBJ_NEW( 'IDLanROI',( *ent.vertices)[0,*] ,(*ent.vertices)
[1,*] )

;Apply ComputMask method
maskResult = myroi -> ComputeMask(DIMENSIONS = [s[0],
s[1]],MASK_RULE=2)

; Here starts the problem; I have a 5000x5000 raster (img) and the
image coordinate system start with [0,0] but the myroi coordinates are
much higher (eg 227984.00 ; 991472.00) Thus everything is masked.
;There is a keyword LOCATION for ComputeMask but I am not sure how to
use it and where to get the right values for it

index= WHERE(maskResult gt 0)
subset=img(index)

OBJ_DESTROY, myshape
OBJ_DESTROY, myroi

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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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