Wetland Mapping: Exercise 3 – Classification of Object Based Image Analysis (OBIA) polygons ArcMap 10

Note: In the following instructions you will be asked to browse the directory location of your Wetland Mapping training folder. That location is represented by a drive letter of x: Please note that the screen shots used in the examples were created utilizing data that was located on C:\temp (i.e. the value of x: was C:\temp). Be sure to use the actual drive letter assigned by the computer to your flash drive and be aware that your screens will reflect that letter and not C:\temp as in the samples. Check with your instructor for more details if you have questions.

If you have not already done so, our first step is to verify the work areas are set up properly. In the Arc Map 10 main menu bar, click on the Geoprocessing menu and in drop down, click on the Environments… button:

Click on Workspace:

Verify that the Current Workspace is your class OutputData folder and that the Scratch Workspace is set to the ScratchArea folder in your Wetland training folder.

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Your screen should look like:

Click OK on this window and click OK on the Options window and you’re set to go for the rest of the session. Now that the environments are set we can begin our processing steps.

From the main menu bar, click on the File menu and click on Open

In the Open window, browse to x:\WetlandMapping\Exercise3.mxd and click on that icon to open the ArcMap document for this exercise. Your screen should look something like:

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You should see a false color infrared image of the north-west side of the Chanhassen study area. In addition to the Object Based Image Analysis (OBIA) polygons and NAIP data, we will add the wetland layer classification that you created in Exercise 2. The wetland layer created in Exercise 2 will help to ease the process of classifying the OBIA polygons.

• Click on the Add Data icon in the ArcMap standard tool bar • Browse to the raster wetland.img in ClassData folder of your Wetland

Mapping folder

and double click on the icon; You should see the following in the Add Data window:

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Please take a few minutes to explore the data. Try different band combinations for the NAIP08.img layer and swipe layers between the OBIA_polygons, the wetland classification layer and the NAIP imagery.

Classifying OBIA polygons

In this exercise, we will classify a set of OBIA polygons as either upland or wetland. The OBIA polygons were created using NAIP imagery and lidar DEM data. These polygons were generated in eCognition Developer software using the multiresolution segmentation and spectral difference segmentation algorithms. An explanation of how those algorithms work is beyond the scope of this exercise, but feel free to ask the instructors if you'd like more information.

Our first step is to activate the editor in ArcMap to begin classifying the OBIA polygons.

• Click on the editor icon in the ArcMap standard tool bar • Click on the option Start editing and select the OBIA_polygons, then click OK

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The editor options become activated and your screen should now look something like this:

Our next step is to open the attribute table of the OBIA_polygons layer.

• Click on the Attributes icon in the ArcMap standard tool bar

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Your screen should now look something like this:

We’re now ready to classify the OBIA_polygons as either upland or wetland. The following is an example of your assignment for this exercise:

Click on the Edit tool icon in the ArcMap standard tool bar

Using the Edit tool, select one polygon located on the left side of the big lake, please see image below to locate the polygon:

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Notice that field information for that polygon has been displayed below the Colum of your attribute table. Click on the type field, Attribute information for this polygon and type wetland.

You can use a Zoom in to see more details about this polygon; your screen should now look something like this:

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Try to classify all the polygons greater than 11 acres (look at the attribute table to identify all the polygons > 11 acres. How many polygons are there? How do we check how many we have done and which ones are left?

Please save edits when you finish identifying the wetland polygons > 11 acres. Compare your classification with the reference data polygons developed by the city of Chanhassen. The city of Chanhassen completed a wetland mapping inventory update in the fall of 2004, and the growing season of 2005. This inventory was done using a combination of field work and photo interpretation from recent aerial photographs.

Click on the Add Data icon in the ArcMap standard tool bar

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• Browse to the vector lakes and wetlands layers in Anwers/CityReferenceData folder of your Wetland Mapping folder

• Add both layers; You should see the following in the Add Data window

• Your screen should now look something like this:

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What mistakes did you made (if any) and how could you do better in the future? What other type of data or software/processes/knowledge would have been useful to have right now to facilitate the process of classifying the OBIA polygons? This concludes Exercise 3.

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