Global warming is a challenging topic. Not only challenging for middle and high school students, but for scientists as well. This topic involves extremely complex, difficult to visualize mathematics that include numerous environmental variables occurring on all scales from the molecular to the global. This is why we chose it as the central theme for a virtual environment.
Virtual reality allows us to gain firsthand experience with complex phenomena of great scope and varying scale while at the same time maintaining control over the variables involved. Students using the Global Warming world will be able to visit places and contexts that do not exist, take measurements, make observations, and control the very rules that nature follows.
We started the planning process by choosing some goals for both what the environment would achieve, and for what participants would take away with them (see a list of the Ecological Variables involved). Next we chose a setting, and created storyboards of what we wanted to have happen in the environment, and the experiences that would be available. The storyboards helped us to create a design document with descriptions of the world, all the objects that would be part of it, and how they would behave. Finally, we would be able to fine-tune this design according to the constraints presented by our development system.
We started by setting some educational goals for the Global Warming world.
Next we stated some more specific goals for the environment. While visiting the Global Warming World, students will be able to:
Once we had established goals, the next step was to choose the setting or settings for the experience. One of the primary advantages of virtual reality is the ability to convey spatial relationships. Accordingly we chose to base our environment on a three-dimensional map of Seattle based on topographical data. Using a familiar setting has a host of advantages including a "recognition factor" where a participant, soon after being immersed in the environment will be able to say: "I know where I am!" The participants bring their set of associations into the simulation with them, which will tend to make it all the more real for them, and perhaps make them care a bit more about the virtual place that they visit. This is an especially desirable characteristic, given the topic.
The next step was to think of the interactions that are called for by our goals and create sketches or storyboards. This step is rather like planning a movie or a play, as you can use storyboards both as a design guide and to construct a list of objects to be acquired or constructed. Storyboards diagram the specific interactions that embody your goals. In our case they depicted the interactions we wanted to provide, for example: Measuring water temperature, changing the number of cars on the road, and traveling through time.
The storyboards helped us to determine the virtual tools we would need, the types of information displays we would use, the controls we would need to provide, and the objects that all of these would require. The next step was therefore to create a large list of all of these items. Since we were doing this in the context of a interface research laboratory, we generated this list in HTML format, and put it up on the web. This would make it accessible from whatever workstations or networked personal computers we might use to build the different aspects of the environment. Linking in descriptions of each object-- a description of its appearance, properties, an how it would behave-- evolved this simple list into a hypertext design document.
See Global Warming World's HTML-based Design Document
The raw materials of virtual environments are pixels, polygons, and sound samples. The resources you have to handle these raw materials are memory and processing power. When building a virtual environment, you must gain an understanding of the resources you have available, and design your environment within those constraints.
We designed the Global Warming world to run on a Division Provision 100 VPX-2 computer. This system has the following constraints:
| Rendering Speed | 600,000 polygons/second |
| Texture Memory | 1 MB |
| Max. Texture Size | 256x256 (must be square) |
| Random Access Memory | 16 MB |
The rendering speed of the computer system determines how much
detail can be visible on the screen at any given time (see What
is VR, section on Computer
hardware). From the rendering speed you can determine the number
of polygons that characterizes this complexity:
The number of polygons per second quoted by the manufacturer is
usually the theoretical maximum given optimal conditions (such
as all polygons are small triangles and part of a single mesh).
Since this is rarely the case the actual performance can be significantly
lower. Also, 20 views per second (also called 20 frames per second)
is a minimum. It is generally better to strive for 30-60 frames
per second. A revised formula looks something like this:
Using this formula (and prior experience with the platform) we determined our total polygon budget to be 5000 polygons. One we had this number, we could go down the list of objects and allot a ration of polygons to each.
Sometimes, we can get away with using a picture of an object instead of creating a 3-D model of the object. Textures can appear in a virtual world with the help of a single polygon on which to "map" the texture. Imagine a brick face on a building. If each brick was actually modeled in 3-D, we would spend 6 polygons per brick (actually 12 triangles: two per face). After just 400 bricks we would have nearly spent our budget creating a single wall. If instead we use a picture of a brick wall and apply that as a texture to the building, a wall that might have used up our entire triangle budget can cost us only two triangles. There is a trade-off, in that if we are not frugal, this brick texture could cost us up to 1/4 of the texture budget.