Execute a Decision Tree

To interactively execute and edit a decision tree:

1. From the ENVI Decision Tree dialog menu bar, select Options > Execute. The Decision Tree Execution Parameters dialog appears.
2. To spatially subset your data, click Spatial Subset.

3. Select output to File or Memory. If your data are georeferenced, also select which image to use as a base image, enter an output pixel size, and select the resampling method from the drop-down list.

   Each node changes to a green color while the decision tree is processing. The classification results appear in a new display group. ENVI saves a temporary file for each node so you do not need to recalculate the results each time you execute the decision tree.

4. To see details about the number of pixels at each node, right-click in the background of the Decision Tree dialog and select Zoom In. Each node lists how many pixels survived to reach that node. The status bar also provides details when you position the cursor over the class.

5. To make any changes to the decision nodes, click the node button and change the expression in the Edit Decision Properties dialog.

   To change the output class color and name, click the class node button and enter the new name and color in the Edit Class Properties dialog.

   For other interactive options, see Decision Tree Options.

6. Execute the decision tree again and look at the results.
7. Repeat steps 4 through 6 until you are satisfied with the results.

Decision Tree Options

You can access decision tree menu options from either the Decision Tree dialog menu bar Options menu, or by right-clicking on the background of the Decision Tree dialog. The choices are:

• Rotate View: To switch between viewing the decision tree graphics as either a vertical tree or a horizontal tree.
• ZoomIn: To zoom into the decision tree. When fully zoomed in, the number of pixels that survive each node is shown on the node.
• ZoomOut: To zoom out of the decision tree. If you have a large tree, you can zoom out to see more of the tree in the window. The number of pixels surviving to each node will not be shown in the classes, but are visible in the status bar when you position the cursor over the class.
• Assign Default Class Values: To reassign the class numbers and colors in order from left to right in the decision tree.
• Hide/Show Variable/File Pairings: To hide or show the Variable/File Pairings dialog.
• Change Output Parameters: To open the Decision Tree Execution Parameters dialog where you can change the output parameters ENVI uses when it executes the decision tree.

Decision Tree Node Options

The decision nodes and class nodes have menu options that you access by right-clicking on the node button. The options are as follows:

• Prune Children: To temporarily remove the children below a decision node and combine all their classes into a single class. Pruned children only apply to the current ENVI session; they will not appear in a saved decision tree.
• Restore Pruned Children: To restore pruned children to a decision node.
• Delete Children: To permanently delete the children below the decision node and change the node into a class node.
• Add Children: To add children and change the class node into a decision node.
• Edit Properties: For decision nodes, to change the node name and expression in the Edit Decision Properties dialog. For class nodes, to change the class name and color in the Edit Class Properties dialog.
• Survivors to Mask: To save the surviving pixels to a mask file. Enter the filename in the Output Survivors to Mask Filename dialog when it appears.