Work with Layers and Views
Lesson content
Lesson 1 of 1
Work with Layers and Views
In this quick guide, you will:
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Open and display an aerial orthophoto. * •
Use the Data Manager to view individual image bands. * •
Use the Cursor Value tool to view pixel information for multiple image layers. * •
Create and link multiple views, each with different image layers.
Sample Data
Download sample data below. Then extract the contents of the .zip file to a local directory.
[GettingStarted.zip
116 MB
DownloadArrow down with horizontal line beneath it](assets/GettingStarted.zip)
- 1
Select File > Open from the Menu bar. An Open dialog appears. 2. 2
Go to the location where you saved the sample data. Select CentralParkOrthophoto.dat and click Open. 3. 3
Press the F12 key on your keyboard to view the full extent of the image. This is a true-color High Resolution Orthoimage from the U.S. Geological Survey.
The Layer Manager shows datasets that are displayed in the view. Since there is only one view (you will learn about multiple views later), the image layer is listed under a single View category. The CentralParkOrthophoto.dat layer lists the bands (1, 2, 3) that are used to display a true-color composite.
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Click the Detach button in the Layer Manager to detach it from the application. It becomes a floating window that you can resize and move to a different location. 2. 6
Click the Data Manager button in the Toolbar.
The Data Manager lists the datasets that are currently open in ENVI. For images, it also lists the available bands. Since the associated header file for this image (CentralParkOrthophoto.hdr) contains wavelength information, the Data Manager also lists the wavelengths for each band.
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Select Band 4: Near infrared and click the Load Grayscale button. The near-infrared band appears in the view, and the Layer Manager shows that a second image layer has been added to the view.
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To toggle between the two images, uncheck the [1] CentralParkOrthophoto.dat layer in the Layer Manager to turn the layer off. Then check the layer to turn it back on. 2. 9
Click the Cursor Value button in the Toolbar. Red crosshairs appear in the display, along with the Cursor Value dialog.
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Click anywhere in the image. The red crosshairs move to that pixel location, and the Cursor Value dialog reports the data values from the grayscale image layer and the true-color layer for that pixel.
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Close the Cursor Value dialog. 2. 12
In the Data Manager, enable the Load in New View option. 3. 13
Right-click on CentralParkOrthophoto.dat in the Data Manager and select Load CIR. A second view is added to the view, which contains a color-infrared version of the orthophoto. The Layer Manager shows that a second view has been added.
Having two views provides a convenient way to compare images side-by-side. However, notice that when you zoom or pan in one view that the other view remains the same. You will need to establish a geographic link between the views.
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Close the Data Manager. 2. 15
From the Menu bar, select Views > Link Views. 3. 16
In the Link Views dialog, click the Link All button, then click OK.
Now when you zoom or pan around one view, the second view moves accordingly.
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Now is a good time to save the view layout. If you close and restart ENVI, it will not remember the layers and views that you last displayed. From the Menu bar, select File > ENVI Session > Save/Restore. 2. 18
In the output file dialog, navigate to a directory where you want to save the file, and name it TwoViews.json. 3. 19
Click Save. If you close ENVI at a later time, you can restore the views and layers from this step by selecting *File > ENVI Session > Save/Restore from the Menu bar*. 4. 20
Click inside of the view that contains the grayscale and true-color image layers. A cyan border surrounds the view to indicate that it is the currently selected view. 5. 21
From the Menu bar, select Views > One View. The color-infrared view is removed. 6. 22
In the Layer Manager, right-click on [1] CentralParkOrthophoto.dat and select Remove. Now the view only contains the true-color image.
This concludes the exercise.
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