Working With DEMs

 Working With DEMs

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DEM files contain a large number of points and would be difficult to use them all with cave. Before you can use a DEM file with a cave, you must select a portion of the DEM that lies above the cave. To help you do this, the DEM Reader displays and image of the DEM on the screen. Once

 

Displaying A DEM. Displaying a DEM file is very simple. Just select "File|Open DEM File" from the menu bar. After you have selected a file, you will be presented with a window that allows you to select the Display Mode you want.

 

These files are very large, (they can contain as many as 1.5 million points) and as a result, it can take several minutes to display the file on a slow computer. As the file is read, you will see the screen being painted one stripe at a time. You can also see the Column Count (in the lower right hand side of the screen) increment as the file is read. There are 1201 columns in a one degree DEM file. Because of the fact that drawing is slow, you can interrupt or stop the process at anytime. To stop the process, click on the "Stop Sign." There will be a slight delay before the program notices the click. Also, you can access the scroll bars or the menus while the view is being drawn.

 

Examining The Terrain. After the terrain has been displayed, you can analyze the terrain in detail. There are several tools to help you. First, the scroll bars at the edge of the window allow you scroll parts of the image into view. As you scroll, the coordinates of the corners of the map are display at the corners of the image. Also, the coordinates of the mouse cursor are displayed at the bottom of the screen. Coordinates will displayed in longitude and latitude for one-degree maps and UTM for the 7.5 minute maps.

 

Zooming. You can use the mouse to select a portion of the screen for more detailed examination. Just press the left mouse button and drag. A box will form on the screen. You can zoom into this box by clicking on the "zoom" button. Because of the granularity of the data, there is a limit to how far you can zoom in with "zoom" button. But, when you do the actual linking, you will be able to use higher zoom factors to accurately link to the cave.

 

Linking. The next step in the process of attaching the surface information to the cave is called linking. Click here for detailed information about the process.