What is GeoView?

GeoView is a 3-D Visualization tool used to view geographic data in the CAVE. It allows the user to view and navigate through a digital elevation model (or DEM) that can be overlaid with a map, an aerial photo, or another texture mapping source. It was created as a Performer CAVE application and it uses version 2.2 of the Performer libraries. GeoView has been used on various projects, including the visualization of the city of Morgantown, West Virginia.(For more information on the CAVE, visit the Virginia Tech CAVE website at www.cave.vt.edu). This website will attempt to illustrate various aspects of GeoView and explain how they are used. It will start with a look at the input file types used and how to import them into the tool. From there we will continue to controls, navigation and examples.

Table of Contents:

• Introduction: What is GeoView
• Part #1: File Types
• Part #2: Bringing the Files into GeoView
• Part #3: Working With the Data
• Part #4: Navigation in GeoView
• Part #5: Screen Captures and Videos

Part #1: File Types

GeoView has two main input sources:

• A DEM.
• A texture map (aerial photo, satellite image, map)

The DEM

A DEM grid file that will be used in GeoView must be a text file with the extension .elev that contains a special header. This text file should have a total of three lines of text with a carriage return at the end of each one. The first two lines of text constitute the header of the file and give the number of columns in the first line and the number of rows in the second line. The elevation values should all be on one line of text and separated by only spaces. Also, the elevation values must be integers in order for the file to work correctly. The size of grid that can be handled by GeoView is limited to 500x500. A sample elevation file is shown below:

The Texture Files

Texture files can be anything from aerial photos and maps to a graduated color map of the DEM. Maps can be used separately as an addition to the DEM with the use of one of the icons in GeoView (to be discussed in Part#3: Working with the data). Any texture file used in GeoView must be in Classic SGI Image (.rgb) format and have edge sizes equal to powers of 2 (256x256, 512x512, etc....). Even if the original image may appear compacted in one dimension, the image will still work correctly. GeoView takes the texture image and stretches it to completely cover the surface of the DEM. Therefore, if you are working with a rectangular shaped DEM, save the image as a sqaure .rgb file and it will appear correctly. The .rgb images used for the Wytheville project are shown below:

Part #2: Bringing the Files into GeoView

The text in the table surrounded by parentheses is what the user must input to the .config file. The most important line of text in this file that must be edited to bring in new data are the map_tex line and the elev_data line. This is where the user must input the paths to the map and the elevation data file

When the .elev file is loaded, GeoView generates a series of triangles between adjacent rows which are used to form 10x10 sections with varying levels of detail. When the user is viewing the data, the sections are rendered with the appropriate level of detail depending on their distance from the viewer. The sections that are farther away are rendered in a low detail level and the sections that are close to the viewer are rendered in with the highest detail level. This reduces the rendering time required and allows for smoother motion. (See Reference #2)

The .texture file is a simple file format which tells GeoView the paths to the desired texture files. The basic format of the file is shown below (Table from Reference #3):

Another file that may be used to edit the look of the GeoView interface is the .icons file. This file allows the user to use different icons to switch between texture files and interact with the interface. The basic format of this file is shown below (Table from Reference #3):

Once these files have been modified to include the new data, the executable file ("WVdemo" for the Morgantown project) can be run to open GeoView and display the terrain model. The GeoView logo will appear in the interface. Simply click any button to procede to the data visualization.

Part #3: Working With the Interface

This image shows the basic interface after lauching GeoView with the Wytheville data. The black and white image has been overlaid on the DEM. The white box represents the cave walls in which the user stands.

	The red stick in the middle of the screen represents the wand used for navigation. The pointed tip of the wand points in the direction of travel.
	On the left side of the screen, there is a column of icons with the following uses: Icon #1: Grid - Allows the user to view the DEM in either solid form or wireframe. Icon #2: Textures - Allows the user to select a texture to be applied to the DEM from a the list defined in the .texture file. Once a texture is selected, it is overlaid onto the DEM. Icon #3: 2D Map - Allows the user to add the 2D map that was defined in the .config file. Icon #4: Query - This turns the Query Mode on or off. The Query mode allows a user to query information from the terrain model by pointing the wand. Icon #5: Reset - This resets the viewer's head and wand to the default position.
	In the bottom right hand corner of the screen is a compass that follows the orientation of the user. The flat, red square represents the datum of the terrain and contains arrows pointing toward the four cardinal directions. The vertical arrows that are perpendicular point in the up and down directions.

Part #4: Navigation in GeoView

Because GeoView is a CAVE application, it can be run in the CAVE itself or in a simulation mode. In the CAVE environment, there is a basic, white box that defines the walls of the cave in which the head can be moved around. If the box is smaller than the object(s) of interest, the box itself can be navigated through the data. Movement in the CAVE setup is controlled using a wand with a pressure-sensitive joystick pad (See Reference #2). As mentioned above in Part #3, the long axis (y-dimension) of the wand inditcates the direction of travel. The y-dimension of the pressure pad controls the user's velocity.

The wand itself has three buttons: One on the right, one in the middle and one on the left (called 1, 2 and 3 from left to right). Any of the buttons can be used to clear the title screen and bring up the data. The left button can be used in conjunction with the y-dimension of the joystich for elevator navigation. Pressing the right button and moving in the joystick's x-dimension allows the user to rotate the data. To exit GeoView, the user presses all three buttons simultaneously (See Reference #2).

The Simulator mode can be used by setting the simulator configuration option in the .cshrc file to "Yes". In this mode, the keyboard and mouse are used to navigate through the data. Below is a table showing the key and mouse combinations used for movement (See Reference #4).

Part #5: Screen Captures and Movies

Screen captures, movies, and/or videos can be very useful in project presentations and lectures. The method used to create these files depends on the environment being used to view the data. In the CAVE, a scan-converter can be used that records the front wall of the cave to produce single .rgb images or videos.

In the CAVE simulator mode, the user has many options. First of all, screen captures can be taken using a special feature made to capture .rgb files. This feature outputs each frame of the simulator as .rgb files that can either be used separately or together to create a movie or animation. Another option for screen captures only is the use of ALT + PrintScreen to capture the window. This allows the user to paste the screen into an image editor or a word processor for presentation. Both movies and images can be captured using MediaCapture software that allows for capture of a window or a selected area. (The screen captures in Part #3 were created using this method.) Below are two movies that were created using MediaCapture. The first one shows the DEM with the aerial photo as the texture map. The second shows the DEM with the color GIS picture as the texture map. (These files were compressed (and converted to .avi) using Media Convert):

AVI format or Quick Time Format	AVI format or Quick Time Format