Exercise 1: Draping an image over a terrain surface

Complexity: Beginner Data Requirement: Installed with software Data Path: See Copying the tutorial data Goal: Familiarize with the navigation tools to preview data, and setting layer properties to drape imagery.

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.

Steps:

1. Start ArcCatalog by clicking Start > All Programs > ArcGIS > ArcCatalog 10.
2. Click Customize and click Extensions.



3. Check 3D Analyst.
4. Click Close.

Previewing 3D data in ArcCatalog

Before you drape the image, you’ll browse to the terrain data and preview it in ArcCatalog.

Steps:

1. Navigate to the 3DAnalyst folder connection in the Catalog Tree.
2. Double-click 3DAnalyst.
3. Double-click Exercise1.



You see a folder called Data and a TIN layer called Death Valley Terrain.

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.

4. Click Death Valley Terrain.



5. 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.
6. Click the Preview drop-down arrow and click 3D View.



7. Right-click above the preview window and click 3D View Tools.



The preview becomes a 3D preview, and a new set of tools appears on the 3D View Tools toolbar.



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.

8. Click inside the 3D preview and drag to the right.



The data rotates around its center. The Navigate tool also allows you to zoom in and out and pan across the data, depending on the mouse button that you click while dragging in the 3D preview.
9. Right-click the 3D preview and drag down.



The pointer changes to the Zoom In/Out pointer, and the view zooms in to the data.
10. Click the middle button—or both the right and left buttons if you have a two-button mouse—and drag to the right.



The pointer changes to the Pan pointer, and the view pans across the data.
11. Click the Identify button and click on the TIN.



The Identify Results window that appears shows you the elevation, slope, and aspect of the surface at the point you clicked.
12. Close the Identify Results window by clicking the top right x.



13. Click the Full Extent button.



The view returns to the full extent of the data.

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.

Steps:

1. From ArcCatalog, click the ArcScene button on the 3D View Tools toolbar to launch the application.



2. 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.

This location will be used for output spatial data generated in the tutorial exercises.



3. Click OK to close the Getting Started dialog box.
Note that many of the tools on the ArcScene Standard toolbar are the same as the 3D navigation tools that you see in ArcCatalog.



4. Close ArcCatalog.
5. On the right side of the ArcScene window, move your pointer over the Catalog tab or click the Catalog tab
The Catalog window slides into the view, ready for use.
6. Navigate to the Exercise1 folder in the Folder Connections path where you locally saved the tutorial data.
7. Click the Death Valley Terrain layer and drag it into the 3D view area of ArcScene, then release the mouse button.



The TIN is drawn in the new scene, and the TIN layer is automatically added into the table of contents.



8. Navigate to the Data folder inside Exercise1 from the Catalog window.
9. Click the dvim3.TIF layer and drag it into the 3D view of ArcScene, then release the mouse button.



The image is added to the scene.



The image is drawn on a plane, with a base elevation value of zero. You can see it above the Death Valley terrain surface where the terrain is below 0 meters elevation (sea level); it is hidden by the terrain surface everywhere else.
10. Uncheck the Death Valley Terrain layer.



Now you can see the whole image. The black areas are parts of the image that contain no data and are a result of previous processing to fit the image to the terrain.

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.

Steps:

1. Right-click dvim3.TIF in the ArcScene table of contents and click Properties.



The Layer Properties dialog box appears. You can change how a layer is drawn on a map or in a scene by setting its properties.
2. Click the Base Heights tab.



3. Click the option Floating on a custom surface.
Because the TIN is the only surface model in the scene, it appears in the surface drop-down list.
4. Click OK.
The image is draped over the terrain surface.



Now you will be able to navigate around the image and see the relationship between surface texture, as shown by the image colors, and the shape of the terrain.

Exploring the image

You will use the navigation tools on the ArcScene Tools toolbar to explore the draped image.

Steps:

1. Click the Zoom in button.



2. Click and drag a rectangle around the middle of the image.



The scene zooms to the middle part of the image.



3. Click the Navigate button.



4. Click and hold the scene with the mouse pointer and slowly drag up and to the left.



The scene rotates, and the view angle lowers, so it looks as though you are looking down the valley, past the higher land on the left side of the scene.



Draping the radar image over the terrain surface allows you to see the relationship between the general shape of the land surface and the texture of the rocks and sediment that make up the surface.

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.

Steps:

1. Right-click Scene layers in the table of contents and click Scene Properties.
The Scene Properties dialog box lets you set properties that are shared by all the layers in the scene. These include the vertical exaggeration, the background color, the coordinate system and extent of the data, and the way that the scene is illuminated (the position of the light source relative to the surface).
2. Click the General tab.
3. Type 2 in the Vertical Exaggeration combo box.



4. Click OK.
The apparent height of the terrain is now doubled.
You can now clearly see how the alluvial fan spreads out onto the valley floor, between the larger rocky area at the center of the scene and the smaller rocky area in the foreground at the left side of the scene.

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.

Steps:

1. Click File and click Save As.



2. Navigate to the Exercise 1 folder.
3. Type Deathvalley as the file name.



4. Click Save.
The scene will now be available for you to open later.