You could be
surprised
but,
actually, there are two ways to cut rasters in ArcMap.
The
classical technique is the
“raster clip” (“raster
cutting”) tool in ArcToolbox.
This has been the only procedure for a long time.
But
since version 10, you have at your disposal the “Image
Analysis” tool in the standard toolbar. This tool
contains
also
a way to cut out rasters and pictures.
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 cutting a part
of the orthophoto coastline of the IGN with the
municipalities’ boundaries of Pont-Aven.
First method: ArcToolbox: clip Raster tool
In ArcToolbox (Data
Management> Raster> Raster Processing> Clip), double-click the clip
tool.
Fill in the fields:
Input raster (required) this
is the raster from which you want
to extract a part.
We want to
cut the raster “2011-1820-6787-OL-RGB-L93.jp2”.
Output range (optional) it’s
the boundary of the polygon that you want to extract.
You can select specific
records in the polygon dataset and the cutting
will be done according to this
boundary.
In our case we have selected
the polygon corresponding to the
municipality of Pont-Aven.
Check the box “use the
entities as input for cutting”. This
option indicates ArcMap to use the selected records in
the polygons layer. If you do not check the box, all
the present polygons are used
as
cutting
boundaries.
Raster Dataset output this
is the name of the output (cut raster). Adds
an
extension for the output (.tif, .img, .jpg, etc.) since it is the
extension entered here determines the output raster format.
NoData value (optional) All
pixels that are outside the cutting boundary will default a
NoData
value. When you load
the raster, these pixels will not appear. You can give
another value to make a change.
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)
You have to start by activating
the images analysis toolbar (Window -> Image Analysis). The
window analysis image 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 layer
name is highlighted. If you do not, the clip
button will be greyed out.
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 result of the cutting.
If
you disable the whole raster in
the caption bar, you can see
the result of the order.
All you have to do now is
to save this cut 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 cells and the raster format output. 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 displayed rasters and
speed up 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’ll love this method!!!
