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I'm trying to manipulate an .IGE file, which I understand is a raster data format developed by Erdas Imagine. The data I've downloaded is the National Land Cover Database (NLCD) 2006 Percent Developed Imperviousness data, available here: http://www.mrlc.gov/nlcd06_data.php

I've tried using winzip and winrar to unzip the file, both of which bring up error messages during the unzipping process. Files do appear, however, in the folder I have designated for extracting the files, including an .IMG file. I can load this .IMG file into ArcMAP 10.1 and QGIS 1.8.0. In either of those programs, I can view the image, but I can't clip it to a shapefile, lest error messages appear. I have tried loading this .IMG file into Opticks 4.10.0 32-bit as well, but an error message comes up indicating the opticks cannot find the file it needs to import.

I wonder if I didn't unzip the compressed file properly? Any suggestions will be greatly appreciated, thanks!

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closed as off-topic by PolyGeo, BradHards, Chad Cooper, iant May 22 at 13:56

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2 Answers 2

In ArcGIS you can clip the raster(img file) using a graphic. If you have a polygon layer that you want to use as the clip boundary right click on it and convert feature to graphic. Make sure the resulting graphic is selected and then right click on the raster. You should be able to export and use the graphic to clip. If its not part of the export on raster then try clip under the gel processing. Otherwise you can clip rasters using Spatial Analyst

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I would download the data again. Sometimes large downloads get corrupted. I have downloaded this exact data so I know that it is fine. You should not be getting any errors while unzipping. The ige file is just an indexing file to address large files that exceed 32bit addressing space. The file that you work with is the img.

I would recommend subsetting the data by defining an extent and then clipping it to a specific vector. To do this define an extent by zooming in to the approximate area you are going to subset. Then go to Geoprocessing menu > Environments... > Processing Extent > and select "Same as Display" in the extent drop down. You could also define it as the extent of a preexisting dataset. You can then go to the ArcToolbox > Spatial Analyst > Raster Algebra > Raster Calculator. Then just define an output raster and select your full raster in the expression window. This will create a new raster that is subset to the new extent. This is a fairly "old school" solution but avoids applying vector topology to a large dataset.

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I downloaded the data again and unzipped it on my local drive (before I was using an external hard drive, which may have corrupted it.) Everything worked! The problem I'm having now is with appending raster statistics to polygons. There's a great discussion on this topic on GIS Stack Exchange, but I still some questions it leaves unanswered. Unfortunately, I'm not allowed to ask those questions in the discussion (answers only, not questions) and if I start a new discussion, it will be deleted for redundancy :/ –  Dan Wolf Mar 26 '13 at 16:29
    
@DanWolf, Not sure what statistics your are after but you can use Zonal Statistics as Table and join the resulting table back to the polygon feature class based on a specified ID or the FID. However, be forewarned, I have logged two bugs with ESRI regarding zonal functions on large rasters. –  Jeffrey Evans Mar 26 '13 at 19:52

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