You might be surprised, but there are two ways to clip rasters with ArcMap. The classical technique is the “raster clip” tool with ArcToolbox. For a long time, this has the only one available.
But since version 10 was introduced, there is an “Image Analysis” toolbar available. This tool also offers a tool to clip rasters and images.
The main advantage of the images analysis toolbar is that you can see the final result before exporting it!
We will discuss both methods by clipping a section of the IGN orthophoto coastline with the limits of Pont Aven community.
First method: ArcToolbox: Raster clip tool
In ArcToolbox (Data Management> Raster> Raster Processing> Clip), double-click the clip tool.
Fill in the fields:
Input raster (required)it’s the raster from which you want to extract a section.We want to clip the raster “2011-1820-6787-OL-RGB-L93.jp2”.
Output range (optional) is the limit of the polygon you want extract. You can select specific records in the polygon data set and the clipping will be executed following this limit. In our case we have selected the polygon corresponding to the municipality of Pont- Aven.
Check the box “use the entities as input for clipping”. It is this option that tells to ArcMap to use the selected records in the polygons layer.If it is not checked, all polygons present are used as clipping mimics.
Raster Data set output this is the name of the output (clipped raster). Add an extension for the output (.tif, .img, .jpg, etc.) because it is the extension entered here that determines the output raster.
Value NoData Value (optional) All pixels that are outside the clipping limit will default a NoData value. When you load the raster, these pixels will not appear. This can be changed by giving another value to it.
Run the tool by clicking OK. The output raster will be cut according to the Pont Aven polygon.
Second Method: Raster Clip (Image Analysis Toolbar)
Firstly, you must activate the analysis images toolbar (Window -> Image Analysis). The image analysis window will be displayed in ArcMap.
This opens the Image Analysis window.
In the image analysis toolbar, select the raster that you want to extract. Make sure the box is checked and that the name of the layer is highlighted. If you do not, the clip button will be grayish.
The Clip button is the first button in the “Processing” section.
As soon as you press the button, a new (virtual) layer is added to the legend bar with the clipping result.
If you disable the full raster in the caption bar, you can see the result.
All you have to do now is to save the clipped raster: right click on the new virtual layer -> Data -> export data : Choose the location and name of the file you want to save . You can also change the size of the cells and the output raster format. Click Save.
This second method can also be used without creating a definitive raster. You can simply use it to reduce the size of the rasters displayed and, therefore, speed your work.
Once the Virtual layer is created , you can delete the original raster legend window and work on the subset instead of the original.
If you have to work with LIDAR data , you will love this method !!!
