Exercise 1: Draping an image over a terrain surface
Viewing a remotely sensed image draped over a terrain surface can often lead to greater understanding of the patterns in the image and how they relate to the shape of the earth's surface.
Imagine that you're a geologist studying Death Valley, California. You have collected a TIN that shows the terrain and a satellite radar image that shows the roughness of the land surface. The image is highly informative, but you can add a dimension to your understanding by draping the image over the terrain surface. Death Valley image data was supplied courtesy of NASA/JPL/Caltech.
Turning on the 3D Analyst extension
First, you'll need to enable the 3D Analyst extension.
- Start ArcCatalog by clicking Start > All Programs > ArcGIS > ArcCatalog 10.
- Click Customize and click Extensions.
- Check 3D Analyst.
- Click Close.
Previewing 3D data in ArcCatalog
Before you drape the image, you’ll browse to the terrain data and preview it in ArcCatalog.
- Navigate to the 3DAnalyst folder connection in the Catalog Tree.
- Double-click 3DAnalyst.
- Double-click Exercise1.
- Click Death Valley Terrain.
- Click the Preview tab. You can preview your GIS data in ArcCatalog. With 3D Analyst installed, you can also preview some data in three dimensions.
- Click the Preview drop-down arrow and click 3D View.
- Right-click above the preview window and click 3D View Tools.
- Click inside the 3D preview and drag to the right.
- Right-click the 3D preview and drag down.
- Click the middle button—or both the right and left buttons if you have a two-button mouse—and drag to the right.
- Click the Identify button and click on the TIN.
- Close the Identify Results window by clicking the top right x.
- Click the Full Extent button.
A layer is a shortcut to geographic data. It also stores information about how the geographic data should be drawn on a map or in a 3D view.
The Navigate tool is active when you first preview data in 3D. You can see the names of tools by hovering the pointer over the tool.
The Navigate tool allows you to rotate 3D data and change the apparent viewer height by clicking and dragging left and right and up and down, respectively, in 3D preview.
Now you’ve examined the surface data and begun to learn how to navigate in 3D. The next step is to start ArcScene and add your radar image to a new scene.
Starting ArcScene and adding data
ArcScene is one of two 3D visualization environments for 3D Analyst (ArcGlobe is introduced in Exercises 5 and 6). Although you can preview 3D data in ArcCatalog, ArcScene allows you to build up complex scenes with multiple sources of data.
- From ArcCatalog, click the ArcScene button on the 3D View Tools toolbar to launch the application.
- In the ArcScene - Getting Started dialog box, click New Scenes and click the Browse button to set the default geodatabase path to D:\3DAnalyst\3D_Default.gdb.
- Click OK to close the Getting Started dialog box.
- Close ArcCatalog.
- On the right side of the ArcScene window, move your pointer over the Catalog tab or click the Catalog tab
- Navigate to the Exercise1 folder in the Folder Connections path where you locally saved the tutorial data.
- Click the Death Valley Terrain layer and drag it into the 3D view area of ArcScene, then release the mouse button.
- Navigate to the Data folder inside Exercise1 from the Catalog window.
- Click the dvim3.TIF layer and drag it into the 3D view of ArcScene, then release the mouse button.
- Uncheck the Death Valley Terrain layer.
This location will be used for output spatial data generated in the tutorial exercises.
You have added the image to the scene. Now you will change the properties of the image layer so that the image will be draped over the terrain surface.
Draping the image
While the surface texture information shown in the image is a great source of information about the terrain, some relationships between the surface texture and the shape of the terrain will be apparent when you drape the image over the terrain surface. In ArcScene, you can drape a layer— containing a grid, image, or 2D features—over a surface (a grid or TIN) by assigning the base heights of the layer from the surface.
- Right-click dvim3.TIF in the ArcScene table of contents and click Properties.
- Click the Base Heights tab.
- Click the option Floating on a custom surface.
- Click OK.
Exploring the image
You will use the navigation tools on the ArcScene Tools toolbar to explore the draped image.
- Click the Zoom in button.
- Click and drag a rectangle around the middle of the image.
- Click the Navigate button.
- Click and hold the scene with the mouse pointer and slowly drag up and to the left.
Exaggerating the terrain
The valley is a broad area, relative to the height of the terrain, even though the mountains at the edge of the scene are more than 2,000 meters above the valley floor. In order to enhance the sense of depth in the scene, and to bring out subtle features in the terrain, you will exaggerate the height of the terrain.
- Right-click Scene layers in the table of contents and click Scene Properties.
- Click the General tab.
- Type 2 in the Vertical Exaggeration combo box.
- Click OK.
You have added depth to the radar image, explored the general relationship between the data in the image and the terrain data, and enhanced the scene so that you can perceive more subtle variations in the terrain.
Now that you’ve built the scene, you will save it so that you can explore it later if you choose.
Saving the scene
Scenes, also called Scene Documents, are like maps in that they contain information about how the layers that are in the scene should be rendered and where the data is located.
- Click File and click Save As.
- Navigate to the Exercise 1 folder.
- Type Deathvalley as the file name.
- Click Save.