comp.lang.idl-pvwave archive: archive » How to extract pixel values from a GeoTIFF using an Esri Shapefile

Home » Public Forums » archive » How to extract pixel values from a GeoTIFF using an Esri Shapefile

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: How to extract pixel values from a GeoTIFF using an Esri Shapefile [message #74180 is a reply to message #74092]

Mon, 03 January 2011 14:46

guillermo.castilla.ca is currently offline

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

Junior Member

Hi Paul,

If what you want is a mask where the pixels within each polygon have
as DN its ID, there is a simpler way which doesn't require the
IDLanROI class:

;Import GeoTIFF and create mask array
img=READ_TIFF('some_multispectral.tif',GEOTIFF=geokeys,inter leave=2)
psz= mapinfo.ModelPixelSCALETAG[0] ; pixel size
x0= geokeys.ModelTiePointTag[3] - geokeys.ModelTiePointTag[0]*psz
y0= geokeys.ModelTiePointTag[4] + geokeys.ModelTiePointTag[1]*psz
; NB, x0 and y0 are respectively the easting and northing
; of the NW corner of the image
s= SIZE(img, /DIMENSIONS)
mask= LONARR(s)

;import shapefile
myshape= OBJ_NEW('IDLffShape', 'some_esri_multipolygone.shp')

; 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

If instead of the polygon ID you want to store in the mask the
thematic class to which the polygon belongs, you just add attr=iShp-
> IDLffShape::GetAttributes(i) in the beginning of the loop, replace in
the last line of the loop with mask[featis]= attr.(j) (where j is the
position in the dbf table of the field that contains the polygon
class).

Cheers

Guillermo

Report message to a moderator

[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

Previous Topic:	ITools and CentOS 6.7
Next Topic:	Is there a way to tell if program is running within the IDLDE?

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Thu Oct 09 20:11:45 PDT 2025

Total time taken to generate the page: 0.08524 seconds