ENVI Tutorial
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ENVI Tutorial: 3DSurfaceView and Fly-Through3D SurfaceView and Fly-Through 2Files Used in this Tutorial 23D Visualization in ENVI 2Load a 3D SurfaceView 3Open and Display Landsat TM Data 3Open and Display DEM as a Gray Scale Image 3Start 3D SurfaceView 4Interactively Control 3D Visualization 53D SurfaceView Controls Dialog 6Rotation/Scale/Translation Controls 6Surface Properties 6Perspective Controls 9Other Visualization Controls 93D SurfaceView Position Controls Dialog 103D SurfaceView Motion Controls Dialog 11Define Flight Path and Begin Flying 11Build a Visualization Sequence Using Annotation 13Animate Sequence 14Save Visualizations 163D SurfaceView as an Analysis Tool 171ENVI Tutorial: 3D SurfaceView and Fly-Through3D SurfaceView and Fly-ThroughThis tutorial uses Landsat Thematic Mapper (TM) data to demonstrate ENVI’s 3D SurfaceView andfly-through capabilities. The 3D SurfaceView function allows you to overlay a gray scale or color-composite image over a digital elevation model (DEM), interactively change the 3D visualization, andcreate a 3D fly-through. The 3D SurfaceView function also provides limited analysis capabilities.Files Used in this TutorialENVI Resource DVD: D a t a \ b h _ 3 dF i l e D e s c r i p t i o nb h t m s a t . i m g ( . h d r ) Landsat TM saturation-enhanced, RGB composite of Bighorn Basin,Wyomingb h d e m s u b . i m g ( . h d r ) USGS DEM at 30 m resolutionb h d e m s u b . p a t Fly-through path fileb h d ...
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ENVI Tutorial: 3D SurfaceView and Fly-Through
3D SurfaceView and Fly-Through Files Used in this Tutorial 3D Visualization in ENVI Load a 3D SurfaceView Open and Display Landsat TM Data Open and Display DEM as a Gray Scale Image Start 3D SurfaceView Interactively Control 3D Visualization 3D SurfaceView Controls Dialog Rotation/Scale/Translation Controls Surface Properties Perspective Controls Other Visualization Controls 3D SurfaceView Position Controls Dialog 3D SurfaceView Motion Controls Dialog Define Flight Path and Begin Flying Build a Visualization Sequence Using Annotation Animate Sequence Save Visualizations 3D SurfaceView as an Analysis Tool
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ENVI Tutorial: 3D SurfaceView and Fly-Through
3D SurfaceView and Fly-Through This tutorial uses Landsat Thematic Mapper (TM) data to demonstrate ENVI’s 3D SurfaceView and fly-through capabilities. The 3D SurfaceView function allows you to overlay a gray scale or color-composite image over a digital elevation model (DEM), interactively change the 3D visualization, and create a 3D fly-through. The 3D SurfaceView function also provides limited analysis capabilities. Files Used in this Tutorial _ ENVI Resource DVD: Data\bh 3d File Description bhtmsat.img (.hdr) Landsat TM saturation-enhanced, RGB composite of Bighorn Basin, Wyoming bhdemsub.img (.hdr) USGS DEM at 30 m resolution bhdemsub.pat Fly-through path file bhdemsub.ann Fly-through path annotation file 3D Visualization in ENVI ENVI provides numerous tools for viewing and analyzing image data in two dimensions. The 3D SurfaceView tool is the first step toward extending data analysis into three dimensions. The 3D SurfaceView tool allows you to display a DEM as a wire frame, ruled grid or points, or with a gray scale or color image draped over it. You can rotate, translate, and zoom in or out of the 3D surface in real-time using the mouse. You can add each 3D view to a list to use later for animation. Use saved views, or interactively draw a flight path (using ENVI's annotation tool) to fly through the 3D data. You can set the vertical exaggeration, vertical and horizontal view angles, and altitude. The cursor is linked to the draped 3D image, allowing you to extract profiles in the X, Y, and Z (spectral) directions. You can also use the Cursor Location/Value tool in the 3D image.
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ENVI Tutorial: 3D SurfaceView and Fly-Through
Load a 3D SurfaceView If you are running ENVI on a Windows system, you must set the display to 24-bit color mode before starting ENVI. Open and Display Landsat TM Data 1. From the ENVI main menu bar, select File > Open Image File . An Enter Data Filenames dialog appears. 2. Navigate to Data\bh 3d and select bhtmsat.img . Click Open . ENVI automatically loads _ bands 1, 2, and 3 into a new display group. You can adjust the displayed contrast stretch by selecting Enhance from the Display group menu bar.
Open and Display DEM as a Gray Scale Image Displaying the associated DEM is not required, but it is recommended to ensure that you have a matched DEM/image pair. 1. From the ENVI main menu bar, select File > Open Image File . An Enter Data Filenames dialog appears. 2. Select bhdemsub.img and click Open . A gray scale image of the Bighorn DEM is automatically loaded to a new display group.
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ENVI Tutorial: 3D SurfaceView and Fly-Through
Start 3D SurfaceView 1. From the ENVI main menu bar, select Topographic > 3D SurfaceView . A 3D SurfaceView: Select Input Display dialog appears. 2. Select Display #1 and click OK . An Associated DEM Input File dialog appears. 3. Select DEM Elevation under bhdemsub.img and click OK . A 3D SurfaceView Input Parameters dialog appears. 4. Select the desired DEM Resolution (number of pixels) used for the 3D plot. The DEM will be resampled to the selected resolution. Using higher DEM resolutions will significantly slow the visualization and should only be used when sufficient computing power is available. You can select more than one resolution. Typically, you should use the lowest resolution (64) while you are determining the best flight path. Then, use a higher resolution to display your final fly-through sequence. 5. In the DEM min plot value field, enter 1219 . In the DEM max plot value field, enter 1707 . (You can always experiment with different values later if you find you need to cut out background pixels or limit the elevation range of the DEM.) DEM values lower than the minimum value and higher than the max value will not be plotted in the 3D view. 6. Set the Vertical Exaggeration field to 15 . 7. Select the Full radio button under Image Resolution . (If you select Other , the image is resampled to the number of pixels selected for the DEM.) 8. Click OK to start the visualization. A 3D SurfaceView dialog appears with the 3D image.
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ENVI Tutorial: 3D SurfaceView and Fly-Through
Interactively Control 3D Visualization
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Click-and-drag the left mouse button in a horizontal direction to rotate the surface around the z-axis. Click-and-drag in a vertical direction to rotate the surface around the x-axis. Click-and-drag the middle mouse button to translate, or pan, the image in the corresponding direction. Click-and-drag the right mouse button in a horizontal direction to zoom in or out. Double-clicking on a pixel in the 3D SurfaceView moves the Zoom window to that pixel. Double-clicking links the 3D cursor location to selected functions that are active in the display group (see "3D SurfaceView as an Analysis Tool" on page 17 for more information). You can also control the rotation, translation, and zoom factor; and reset the 3D view to its original position, using the SurfaceView Controls dialog described in the following section.
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ENVI Tutorial: 3D SurfaceView and Fly-Through
3D SurfaceView Controls Dialog Access the 3D SurfaceView Controls, Position Controls, or Motion Controls dialogs from the Options menu of the 3D SurfaceView dialog. These dialogs determine how the surface is displayed, how the perspective is positioned, and how the surface is animated, respectively. The 3D SurfaceView Controls dialog allows you to make fine adjustments, to edit surface properties, and to rotate the surface around a perspective view. Rotation/Scale/Translation Controls 1. From the 3D SurfaceView dialog menu bar, select Options > Surface Controls . The 3D SurfaceView Controls dialog appears. 2. Click the buttons to change the rotation of the surface plot in the desired direction. Use the adjacent Inc field to set the rotation increment. 3. Click the buttons to zoom in or out of the surface plot, respectively. Use the adjacent Inc field to set the zoom increment. 4. Click the buttons to move (translate) the surface plot in the desired direction. Use the adjacent Inc field to set the translation increment. Surface Properties 1. Click the Surface Style drop-down list and select different wireframe options. The figures below show Wire (upper-left), Ruled XZ (upper-right), Ruled YZ (lower-left), and Points (lower-right). 2. Experiment with different Vertical Exaggeration values. Higher factors increase the vertical exaggeration.
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ENVI Tutorial: 3D SurfaceView and Fly-Through
Perspective Controls This section of the 3D SurfaceView Controls dialog allows you to click a point in the 3D SurfaceView plot to specify a perspective origin around which the surface is rotated. 1.Clickthebuttontotogglethecursorto"select"mode. 2. Move the cursor to the 3D SurfaceView plot and click somewhere in the plot to set the origin of the rotation. The view zooms to the new origin of the perspective, which is set at a height that is 0.05 normalized units (default) above the surface. Rotation begins. 3. You can modify the height of the perspective origin above the surface using the Translation controls in the 3D SurfaceView Controls dialog. 4. Click Stop to pause the current rotation. If the cursor is in "select" mode, but you did not choose a perspective origin, clicking Stop toggles the cursor out of "select" mode. 5. Click Start to start a rotation that was stopped; or, if no perspective rotation was started, to begin rotating the surface around its center point. 6. Enter the desired value for Rotation Delay , which is the number of seconds to wait between the successive renderings of the rotating surface. The default value is 0.05. Setting the value to 0.0 sets the rotation speed to your computer's limits for calculating the transformation matrix and rendering the surface. 7. You can change the direction of the rotation of the surface by clicking Direction and selecting Left or Right . Direction refers to the rotation direction of the surface, not the viewer's perspective. Other Visualization Controls 1. To change the color of the background in the 3D SurfaceView dialog, select Options > Change Background Color . 2. To smooth a surface that appears pixelated, select Options > Bilinear Interpolation from the 3D SurfaceView dialog menu bar. To turn off the smoothing effect, reselect this option. 3. To reset the surface view to the default view, select Options > Reset View from the 3D SurfaceView dialog menu bar.
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ENVI Tutorial: 3D SurfaceView and Fly-Through
3D SurfaceView Position Controls Dialog Use this dialog to view the surface panoramically (as if you are standing in the image), thus setting the view to a specific position and direction. 1. From the 3D SurfaceView dialog menu bar, select Options > Position Controls . The SurfaceView Position Controls dialog appears.
2. Double-click inside the Display #1 Image window to start the Cursor Location/Value tool. Move the cursor to a preferred viewing position and note the corresponding pixel or map coordinates. 3. Click the Pixel Coord toggle button to toggle between pixel coordinates and map coordinates. Enter the coordinates from Step 2 into the Sample/Line or E/N fields. A good starting point is Sample 3600 and Line 3000. 4. Experiment with different Azimuth , Elevation , and Height Above Ground values to see how they change the 3D SurfaceView. Start with an Azimuth (look direction) of 90 , an Elevation (look angle) of -90 (looking straight down), and a Height Above Ground of 2000 m. Change the height from 2000 to 1000 to 500 . Click Apply . 5. Use the interactive rotation and zooming to see the 3D SurfaceView from the selected viewpoint.
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ENVI Tutorial: 3D SurfaceView and Fly-Through
3D SurfaceView Motion Controls Dialog ENVI’s 3D SurfaceView function can be used to build an animation sequence or fly-through of the 3D visualization. Try restoring a previously saved flight path and playing the animation sequence. 1. From the 3D SurfaceView dialog menu bar, select Options > Motion Controls . The 3D SurfaceView Motion Controls dialog appears.
2. From the 3D SurfaceView Motion Controls dialog menu bar, select File > Restore Sequence . A file selection dialog appears. 3. Select bhdemsub.pat and click Open . 4. Set the Frames field to 500 and click Play Sequence . Click Stop Sequence to stop the fly-through. Define Flight Path and Begin Flying 1. Click Clear in the 3D SurfaceView Motion Controls dialog. Use the mouse or arrow buttons (in the 3D SurfaceView Controls dialog) to select the starting viewpoint, and click Add in the 3D SurfaceView Motion Controls dialog to add this projection as the starting point of the flight path. 2. Use the mouse or arrow buttons to select another viewpoint, and click Add to add this view to the flight path. Repeat this step until you have selected as many visualization steps as desired (at least two are required). When you select the number of frames and play the visualization, the flight path is smoothly interpolated between the different views. A larger number of frames results in a smoother flight path, but it slows down the animation. l Select a view number and click Replace to replace a projection in the flight path list. l Select a view number and click Delete to delete a projection in the flight path list. l Click Clear to clear the flight path list.
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