Better Raster Clipping options in ArcGIS
Many users like the Extract by Mask option that the Spatial Analyst tools provide, however they may want to perform the clip on a multiple band raster or may not have a Spatial Analyst license.
Good news, at ArcGIS 9.3 we have added functionality to clip a raster dataset within the core ArcGIS Desktop tools. Now, the Clip geoprocessing tool and the Export Raster Data dialog box in ArcMap both allow for clipping of multiple band rasters. This post will go into more detail highlighting both methods.
Method 1: Using the Clip Geoprocessing Tool
The raster Clip GP tool has been enhanced to allow you to clip a raster based on the geometry of a feature class. Clipping based on the geometry means that you will use the boundaries of all the features in the feature class to clip the raster and not a minimum bounding rectangle of those features. To perform this, follow the steps below:
- Open the Clip geoprocessing tool in the Data Management tool box
- For the Input Raster parameter specify the raster dataset that you would like to clip.
- For the Output Extent parameter specify the feature class you would like to use as the clip extent (mask).
- Check the Use Input Feature for Clipping Geometry checkbox.
- For the Output Raster Dataset parameter specify the path, file name, and extension.
- Optionally, specify a NoData Value. This is a very good idea when you are clipping with an irregularly shaped feature class. Usually you will specify a value of 0.
Lets look at our data. Below is a raster dataset and feature class. We would like to clip our raster dataset with the red feature class polygon.
If we clip the data with the Use Input Feature for Clipping Geometry box unchecked, then we end up with the minimum-bounding rectangle of the features in the feature class.
However if we check on the Use Input Feature for Clipping Geometry checkbox and we use 0 as our NoData Value, then we end up with the desired result.
Method 2: Using a Map Graphic to Specify Raster Extent
If you do not have a feature class already created, you can simply use the Draw tools to create a graphic in ArcMap and then clip the raster based on the graphic.
To clip the raster based on this graphic, follow the steps below:
- Right-click on the raster dataset in the map's table of contents, point to Data and click on Export Data.
- In the Export Data dialog, make sure that the Selected Graphics option is used. It is a good idea to specify NoData.
- When specifying a NoData value, you will want to use a value that is within your current pixel-depth, and is not currently being used in the image. Usually the value of 0 is chosen.
The end result will be a clipped raster based on the shape of the graphic in map.
Stay tuned for next week’s post, Clipping a raster dataset based on selected features within a feature class.