Feature Analyst Quick Start Guide

Transcription

1 Feature Analyst Quick Start Guide Change Detection Change Detection allows you to identify changes in images over time. By automating the process, it speeds up a acquisition of data from image archives. As with any extraction, it s important to set up good training sets. Follow the steps below to set up an end to end change detection extraction. Change Detection Work Flow Use the Prepare Change Detection Layer menu option to fuse the images into a single input raster. Setup the learning parameters and run the extraction. Be sure to use the change detection raster created above as the input image. If necessary, visualize the change detection raster by selecting different band combinations that highlight the changes over time. Create a new training set and specify examples that reflect the type of change you are trying to extract (features added over time or removed over time). Refine results as needed using Post Processing/Hierarchical Learning to obtain the final object-specific result. Commit data to your geodatabase. 9LVXDO/HDUQLQJ6\VWHPV,QF 32%R[ 0LVVRXOD07

2 Change Detection Feature Analyst Quick Start Preparing a Change Detection Layer 1 Create a new data frame and add the before image (pre) and after image (post). 2 Choose Feature Analyst on the toolbar and select Image Tools from the menu. 3 Select Prepare Change Detection Layer on the Image Tools menu. The Prepare Change Detection Layer dialog box opens. 4 On the Prepare Change Detection Layer dialog box, highlight the pre image and choose the Set Before Image button, then highlight the post image and choose the Set After Image button. 5 Once you have identified the before and after images, choose Create Image to fuse the images and load the newly created raster into the layer. The Feature Analyst Save As dialog box opens, asking you to name the new layer. 6 Select a path in the list box in the center of the dialog box. 7 Enter a name for the new layer in the Filename field. 8 Choose Save. The Change Detection image appears in the active data frame. VISUALIZING THE CHANGE DETECTION RASTER Visualizing the change detection raster allows you to see the changes that have taken place in an image over time. By default, when Feature Analyst loads a newly created change detection raster into the Table of Contents, it automatically sets the displayed bands to be the following: When the input rasters are both RGB color images: The displayed red band is the red band from the before image. The displayed blue band is the blue band from the after image. [ 2 ]

3 Feature Analyst Quick Start Change Detection The displayed green band is the green band from the after image. Input rasters are both panchromatic images a : The displayed red band is the before image. The displayed blue band is the after image. The displayed green band is also the after image. This particular band combination produces the following effects: Areas that have a reddish tint indicate features that removed over time. Areas that have a blue-green tint indicate features that added over time. a. Feature Analyst displays a prompt, asking you if it should add an extra band to the fused raster to allow for better visualization. The added band contains no information and is included so an RGB composite display can be used. To alter the default visualization, double-click on the change detection raster in the Table of Contents and select the Symbology tab. Then, change the band combination. Creating the Training Set To get a good representation of the target feature class, remember to create examples throughout the image. 1 Choose the Create New Feature Layer tool. The Feature Analyst Save As dialog box opens. 2 Enter a name and path for the new layer. 3 At the bottom of the dialog box, select Polygon Shapefile. 4 Choose Save. The new feature layer appears in the Table of Contents. Note: Thought Feature Analyst can work with Point and Line feature layers, it works best with polygons. 5 Choose Editor on the ArcGIS toolbar and select Start Editing on the drop menu. This starts your editing session. [ 3 ]

4 Change Detection Feature Analyst Quick Start 6 Choose the Sketch tool on the ArcGIS toolbar. 7 Using the zoom tools, zoom in on the image and draw a sample polygon. 8 Repeat the previous step until you have adequate training examples. As a reference only, see the example in the margin of a changed road extraction training set. 9 Choose Editor on the ArcGIS toolbar and select Save Edits on the drop menu. 10 Choose Editor again and select Stop Editing. This ends your editing session. Setting Up the Learning Parameters 1 Highlight the newly created shape file and choose Set Up Learning. The Set Up Learning dialog box opens. The Set Up Learning dialog box provides you with two options for setting up your feature extraction. Below we quickly walk you through both options. 2 Do one of the following: Quick Setup: On the Feature Selector tab, select the feature class that most closely resembles the feature you are trying to extract. In our example, you would select Wide Linear Feature. Choose OK to close the dialog box. Fine-tuned Setup Select the Learner Settings tab. In the Input Bands dialog, verify that the change detection raster appears in the Bands Selected list, and that all of the appropriate bands are selected with the correct reflectance data type. [ 4 ]

5 Feature Analyst Quick Start Change Detection If the default Input Representation does not adequately represent your target feature, change the pattern and width to give the best possible spatial representation of the target feature class. If there are areas that you wish to exclude, or specifically include, setup a Region of Interest using the Masking tab to specify a mask and type. On the Learning tab, specify an Aggregation size (this will vary depending on the size in pixels of the target feature), and select Learning Approach 1. Click OK to save the learning parameters and close the dialog box. 3 Choose One Button Learning on the toolbar to begin the extraction. The Feature Analyst Save As dialog box opens. 4 Enter a file name and path for the new layer. 5 Choose Save. The Feature Analyst Training Phase dialog box opens, displaying the progress of the extraction pass. You can choose Pause to pause the process or Cancel to stop it. When the extraction pass is complete, the Pause button changes to OK. 6 Choose OK to close the Training Phase dialog box. The result layer appears in the active data frame in the Table of Contents. For the example shown above, the results will appear similar to the image below. Removing Clutter Automatically If your results come back with a significant amount of clutter, use Feature Analyst's Hierarchical Learning or Post Processing options to clean up the result layer. Removing clutter automatically adds the process to your learning recipe, allowing you to apply it to similar road images. Tip: If you accidentally delete a correct polygon, choose Edit on the ArcGIS menu bar and select Undo. This reverses the previous deletion. AGGREGATING FEATURES 1 Highlight the result layer in the Table of Contents and choose Feature Analyst on the toolbar. 2 Select Post Processing on the drop menu and select Aggregate Features on the Post Processing menu. [ 5 ]

6 Change Detection Feature Analyst Quick Start The Aggregate Features dialog box opens. 3 In the Minimum Polygon Area field, enter a number representative of your road network. We recommend a number between 500 and Choose OK. The Feature Analyst Save As dialog box opens. 5 Enter a name and path for the aggregation shape file. 6 Choose Save. Feature Analyst runs the Aggregation pass. The Aggregation pass eliminates the small polygons. Create Shape File Metrics The Shape File Metrics feature allows you to calculate a variety of metrics for the polygons in your result layers, on the fly. The calculations are entered into the Attributes table for the layer. The feature works on points, lines, and polygons. With point results, you can only select the Mean Height option. To accomplish this, you must have a DEM file for the active data frame. With line results, you will only have access to the Length option. 1 In the Table of Contents, highlight the result layer you want to calculate on. 2 Choose Feature Analyst on the toolbar and select Feature Tools on the drop menu. 3 Select Create Shape File Metrics on the Feature Tools menu. The Create Shape File Metrics dialog box opens, allowing you to select the inputs to calculate for. 4 Select Length. 5 Choose OK on the dialog box. The Feature Analyst Save As dialog box opens, asking you to name the new shape file created from this action. 6 Enter a name and path for the new file and choose Save. [ 6 ]

7 Feature Analyst Quick Start Change Detection Feature Analyst calculates the attributes you selected. The system enters the metrics into the Attributes Table. Viewing Results Once you have calculated your shape metrics, you can view the calculations in the Attribute Table. 1 Right-click on the layer you calculated the metrics for. 2 Select Open Attributes Table on the popup menu. The Attributes table opens, displaying the metrics for the features in the selected shape file. 3 Click the close button (X) to close the dialog box. Commit to Geodatabase Now that you have acquired your complete results, you may want to commit the new geographic data to your geodatabase. WARNING: Make sure that the coordinate systems for both your source and target match. If not, the Commit to Geodatabase tool might not produce the expected result. 1 Choose File on the menu bar and select Add Data from the drop menu. The Add Data dialog box opens, allowing you to find your geodatabase and open the feature class file you want. [ 7 ]

8 Change Detection Feature Analyst Quick Start 2 Browse to the desired Geodatabase and select the appropriate feature class and choose Add. The selected feature class appears in the table of contents in the data frame. 3 Choose Editor on the ArcGIS toolbar and select Start Editing. The Start Editing dialog box opens, asking you to identify the layer to edit. 4 Select the geodatabase from the list and choose OK. 5 Choose ArcGIS Selection tool on the ArcGIS toolbar and draw a stretchy box around the features you want to include in your geodatabase. To select all available features right click on your results shape files, choose Selection, then choose Select All. 6 Highlight the shape file in the TOC that contains the results you want to commit to the geodatabase. 7 Choose Feature Analyst on the toolbar, select Post Processing from the drop menu, and select Commit to Geodatabase on the Post Processing menu. The Commit Data dialog box opens. The feature class you selected previously is highlighted, along with any sub-types attached to the selected class. 8 Verify that the appropriate shape file is listed in the Selected Feature Layer box at the top of the Commit dialog and that the Count reflects the number of features that you want to write to the geodatabase. 9 In the Available Feature Classes box, select a feature class. 10 Choose OK. The system applies the default attributes specified in the geodatabase to the features selected in the workspace. Setting Custom Attributes You can use the Available Feature Classes to fill in the attributes for your features. You can also use them as a short cut to filling in the attributes. You can select a feature class in the list and then [ 8 ]

9 Feature Analyst Quick Start Change Detection edit the attributes that are unique to the data you are working with. 1 Follow steps 1 to 5 above to assign default feature class attributes. 2 Choose Set Custom Attributes. The Attribute Editor dialog box opens over the Commit to Geodatabase dialog box, allowing you to edit the individual data fields. Some fields only allow you to select information already assigned to the field. These are called Domain fields and are limited to the assigned domain data. 3 In domain fields, select an option from the list provided. In non-domain fields, enter your required information. Nondomain fields allow you to enter any information you need. 4 Choose OK on the Commit to Geodatabase dialog box. The dialog box closes and you return to the ArcGIS workspace. Confirming Attribute Assignment 1 Right click the final result layer in the Table of Contents. 2 Select Open Attribute Table from the popup menu. The attributes assigned from the feature class selection appear in the table cells. [ 9 ]

10 Change Detection Feature Analyst Quick Start [ 10 ]