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Feature Mapping: Region Growing Tool MicroImages, Inc. 11th FloorSharp Tower 206 S. 13th Street Lincoln, Nebraska 68508-2010 USA
Voice (402)477-9554 FAX (402)477-9559 email info@microimages.com web www.microimages.com March 2008
Region Growing Tool
Feature Mapping
DRAFT
31 March 2008
Feature Mapping is an interactive image interpreta-
tion process that keeps you, the expert, in the inter-
pretation loop. You identify cells that provide a
reasonable sample of the features you are trying to map and let
the process identify other similar cells using the decision rule of
your choice. These similar cells are called prototype features
and you decide whether to mark the identified features as be-
longing to a class you name. There are two tools for choosing
potential cells for any given feature type: the Define Samples
tool and the Grow and Mark Features tool.
The Define Samples tool identifies a range of cell values for
each layer used for processing or the exact value for each pro-
cessing layer at the location you click. When you decide that
you have provided enough samples to identify the feature type
of current interest, you right-click or click on the Classify but-
ton to create prototype cells from all of the cells in the process-
ing raster(s) that meet the sample criteria. You can then add
additional sample cells or mark the prototype features. To learn
more about this method and its ability to use a reference vector
see the Technical Guide entitled Feature Mapping: Using a
Reference Vector.
Try this new feature now in DV 2008:74
The Grow and Mark Features tool (icon illustrated left) works
on one feature at a timeyou click in a representative area and
the process looks at the neighborhood around the click and de-
termines a basic range. The range can be expanded/reduced
using the mouse wheel (rolling it toward you expands the range
while rolling it away reduces the range). When you are satis-
fied with the prototype feature, right click to convert it to a
marked feature. You can also use the Mark Features tool to
mark these prototypes if you want to introduce protected areas
as illustrated at the bottom of the page.
If the prototype feature is still
growing after a second has
passed or 1,000 cells have
been identified, a window will open that asks if you want to
continue growing the feature or if youd like to start over with
a reduced growth factor. If you click on Cancel, the prototype
is removed. It is recommended that you do your feature grwoing
at 1X zoom (full resolution) otherwise gaps in the prototype
feature may not be apparent and you may get the prompt shown
even though the feature appears complete.
Initial region growing
Range expanded using mouse wheel
Right click to mark (hole filling off)
Once prototype features are identified, you can
easily create protected areas that will not become
part of the feature when marked. Prototype
features, marked features, and protected areas
are mutually exclusive. In the example shown,
there are two islands within the lake. If hole filling
is on (Options/Hole-Filling), these islands will be
part of the feature when it is marked if they are
not protected. Since the prototype feature shown
has been grown to the edges of the islands, you
can simply use the Protect Areas tool to draw any
shape that encloses an island and right-click.
Only the area that is not part of the prototype will
be protected. You do not have to meticulously
draw around the islands. You can then use hole-
filling for the rest of the prototype.
Prototype feature with protected areas
Marked feature with protected areas
These illustrations show how features can be extracted from the 1- or 2-meter color orthoimages collected annually by the USDA (California shown).