Large Caves

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CaveX creates passage models by creating "faces" or "polygons" that represent parts of the passage walls. Each survey shot can generate between 4 and 28 faces. Thus very large caves can generate lots of faces. If the faces count exceeds 64,000, CaveX will split the cave up into more than one mesh. This enables CaveX to deal with very large cave system.


The amount of work that CaveX has to do is governed by the number of faces an image has. For each face, CaveX has to position, color, texture, smooth, light, shade, and draw a separate image. With large caves, this can put a heavy load on your computer and your video card. For example, Lechuguilla Cave, which is about 100 miles (160KM) in length, can generate nearly 1,000,000 faces. Imagine how much work has to be done to display this image 10 times per second. Here is a detailed description of some of the issues you need to be aware of.


1. Memory. Windows has two types of memory: physical memory and virtual memory. Physical Memory is the actual hardware memory that is installed on your computer. Virtual memory is additional "pseudo" memory that Windows creates by saving data to the hard disk.


Modern video cards require that the entire image fit into physical memory. Otherwise, the program would be slowed down by having to read from the disk all the time. Before you display a cave, CaveX warns you if the image will exceed physical memory. You can reduce the amount of memory required to display the image by choosing a simpler model. You can do this by choosing a Square or Diamond model instead of an Octagon or by choosing no Corner Rounding. You can also solve the problem by installing more physical memory.


If you choose display a cave where the size exceed physical memory, the computer my grind to a halt trying to display the image. If the image only exceeds physical memory by a small amount, you may get away with it, because there is a certain amount of compression that takes place before the image is displayed.


2. Speed and Faces. As the size of the image exceeds 64,000 faces, certain operations slow down dramatically. For example, it may take a minute or two to set up the image for displaying. Also, things like texturing, coloring, or changing various display modes may take a long time.


Even so, the actual animation rates can be surprisingly high for large caves. For example, I get animation rates of 10 frames per second and 2,000,000 polygons per second when displaying Lechuguilla Cave on my 450 MHz PIII. On my latest computer, a 2.8 GHZ Pentium IV, I get over 25 frames per second and more than 5-million polygons per second.


4. Video Cards. The Video Card in your computer can have a dramatic effect when you are working with large caves. The newest video cards have special hardware to accelerate the drawing of complex images. They can also have up to 256 megabytes of on board memory, which helps the card deal with large meshes. You may find it useful to upgrade your video card if you are dealing with large caves.