Clipping raster data


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We are running ArcSDE, which keeps all of our GIS datasets in a single geodatabase.  Since we only want to maintain a single set of data, it is not possible under the RMBL system for individuals to edit datasets directly from the geodatabase.  If you want to edit data, you must export the GIS file of interest out of the geodatabase before you can alter it.  To do that do the following:
    Open ArcCatalog > Navigate to Database Connections  > Open GISdatasets.sde > Highlight the file of interest > Right click and choose Export > Select "Raster To Different Format".  Export as ESRI grid, geotiff, or Imagine file.

 Keep in mind that for some editing, you'll need the ArcInfo license, rather than the ArcView license.  If the tool is not available, move to the computer in Barclay classroom with ArcInfo.

   Once you have exported the file, there are several ways to subset a raster. We explain two methods here.  The easiest way is to extract the desired area based on a mask.  If you already have a shapefile created to clip the raster, go directly to II.

I.  If you don't have a shapefile for clipping, you must create one.  Open ArcCatalog > Right click on folder that you have created > Select New > Shapefile.  Enter a name, select polygon, and click Edit to enter the appropriate coordinate system/projection.  You should the same coordinate system as your raster data.  To make sure that you have the same coordinate system, you should import the coordinate system from the raster.  After you click Edit, choose Import > Navigate to where your raster data is stored > Select the raster > Click Add > It will add in the coordinate system > Click Apply, then OK > Then click OK again to create the new shapefile. 

   Add the new shapefile into ArcMap > Click on Editor and start Editing (be sure that your shapefile is selected under the Target field).  Using the pencil tool, draw the area that you wish to clip.  Once this is completed, go to Editor > Stop editing > Save edits.  Once you save these edits, they are finalized. 

II.  Open ArcMap > Open the ArcToolbox (red toolbox) > Select Spatial Analyst Tools > Extractions > Extract by Mask.  In the extraction dialog box, choose the input raster (the one that you want to clip), the feature mask data (the shapefile that you are using to clip with), and choose the location and name of the output raster > Click OK.

III.  You can also clip a raster based on a rectangular extent.  This is useful if your area of interest is a simple square or rectangle, and you can get the corner coordinates.  Open ArcMap > Open ArcToolbox (red toolbox) > Data Management Tools > Raster > Clip > In the Clip dialog box, enter the input raster (the one you want to clip), enter the X and Y mins and max's, and name the output > Click OK.  You should be able to get the X and Y mins and max's by opening your raster in ArcMap, placing your cursor over the upper left and lower right corners, and writing down the coordinates displayed in the lower right hand corner.  The upper left hand corner will give you the min x and max y, and the lower right hand corner will give you max x and min y.