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Once created, the light parameters for the Daylight system, including light intensity and shadows, are located in the Modify panel, but the Date, Time, and Location parameters are in the Motion panel when the light object is selected. You can access the Motion panel parameters by clicking the Setup button in the Daylight Parameters rollout.

Understanding Azimuth and Altitude

Azimuth and Altitude are two values that help define the location of the sun in the sky. Both are measured in degrees. Azimuth refers to the compass direction and can range from 0 to 360, with 0 degrees being North, 90 degrees being East, 180 degrees being South, and 270 degrees being West. Altitude is the angle in degrees between the sun and the horizon. This value ranges typically between 0 and 90, with 0 degrees being either sunrise or sunset and 90 degrees when the sun is directly overhead.

Specifying date and time

The Time section of the Control Parameters rollout lets you define a time and date. The Time Zone value is the number of offset hours for your current time zone. You can also set the time to be converted for Daylight Saving Time.

Specifying location

Clicking the Get Location button in the Control Parameters rollout opens the Geographic Location dialog box, shown in Figure 20.12, which displays a map or a list of cities. Selecting a location using this dialog box automatically updates the Latitude and Longitude values. In addition to the Get Location button, you can enter Latitude and Longitude values directly in the Control Parameters rollout.

The Daylight system also includes an option to set the Sky value from Clear to Partly Cloudy to Cloudy.

FIGURE 20.12

The Geographic Location dialog box lets you specify where you want to use the Sunlight system. You have many different cities to choose from.

Tutorial: Animating a day in 20 seconds

You can animate the Sunlight system to show an entire day from sunrise to sundown in a short number of frames. In this tutorial, you focus on an old tree positioned somewhere in Phoenix, Arizona, on Christmas. The tree certainly won't move, but watch its shadows.

To use the Sunlight system to animate shadows, follow these steps:

1. Open the Sunlight system.max file from the Chap 20 directory on the CD.

This file includes a tree mesh created by Zygote.

2. Add a Sunlight System by selecting the Systems category in the Create panel and clicking the Sunlight button. Then drag in the Top view to create the Compass helper, and click again to create the light. In the Control Parameters rollout (found in the Motion panel), enter 12/25 and the current year for the Date and an early morning hour for the Time.

3. Click the Get Location button, locate Phoenix in the Cities list, and click OK. Rotate the compass helper in the Top view so that north is pointing toward the top of the viewport.

4. Click the Auto Key button (or press the N key), and move the Time slider to frame 100.

5. In the Control Parameters rollout, change the Time value to an evening hour. Then click the Auto Key button (N) again to disable animation mode.

Note

You can tell when the sun comes up and goes down by looking at the Altitude value for each hour. A negative Altitude value indicates that the sun is below the horizon. •

Figure 20.13 shows a snapshot of this quick day. The upper-left image shows the animation at frame 20, the upper-right image shows it at frame 40, the lower-left image shows it at frame 60, and the final image shows it at frame 80.

FIGURE 20.13

Several frames of an animation showing a tree scene from sunrise to sunset

Using Volume Lights

When light shines through fog, smoke, or dust, the beam of the light becomes visible. The effect is known as a Volume Light. To add a Volume Light to a scene, choose Rendering⇒Environment (or press the 8 key) to open the Environment dialog box. Then click the Add button in the Atmosphere rollout to open the Add Atmospheric Effect dialog box, and