Sun and Sky Simulation
The sun is a light that simulates the effect of sunlight and can be used to show how the shadows cast by a structure affect the surrounding area.
Sun and sky are the primary sources of natural illumination in AutoCAD. Whereas the rays of the sun are parallel and of a yellowish hue, the light cast from the atmosphere comes from all directions and is distinctly bluish in color. When the LIGHTINGUNITS system variable is set to photometric, more sun properties are available.
When the workflow is photometric (the LIGHTINGUNITS system variable is set to 1 or 2) the sun properties have more properties available and are rendered internally using a more physically accurate sunlight model. The sun color is disabled for the photometric sun as the color is computed automatically based on the time, date, and location specified in the drawing. The color is determined proceduraly based on the position in the sky. When the workflow is generic or standard lighting (the LIGHTINGUNITS system variable is set to 0), the additional sun and sky properties are unavailable.
The properties of the sun can be modified by using the SUNPROPERTIES command. The Sun Properties window is displayed. The details of the settings are located under SUNPROPERTIES in the Command Reference.
The rays of the sun are parallel and have the same intensity at any distance. Shadows can be on or off. To improve performance, turn off shadows when you don’t need them. All settings for the sun except geographic location are saved per viewport, not per drawing. Geographic location is saved per drawing.
The angle of the light from the sun is controlled by the geographic location you specify for your model and by the date and time of day. These are properties of the sun and can be changed in the Sun Properties window and the Geographic Location dialog box. The time zone used is based on the location, but you can adjust it independently ( TIMEZONE system variable).
The option to choose the sky background is only available when the lighting unit is photometric (the LIGHTINGUNITS system variable is set to 1 or 2). If you choose the sky background and change the lighting to standard (generic) lighting (the LIGHTINGUNITS system variable is set to 0), the sky background is disabled.
The sun and sky background can be interactively adjusted in a view that can be activated in the Sun Properties window by clicking the first button in the title bar of the Sky Properties. This button activates the Adjust Sun & Sky Background dialog box. Here you can change properties and preview the changes to the background.
The view can have a sky background or a sky background and illumination. This option is in the Sky Properties Status drop-down list in the Sun Properties window. Additional sky illumination adds extra light to the scene, simulating the effect of light scattered by the atmosphere throughout the scene. This additional light is only visible in rendered output when final gather is enabled. This can be found in the Advanced Render Settings palette.
The VIEW command provides a mechanism for creating and managing named views. The sun and sky background can be assigned to a new named view under Background. The sky background relies on the sun data in the named view.
You can adjust sun and sky background can be interactively in a view in the Adjust Sun & Sky Background dialog box. Click the first button in the title bar of the Sky Properties. This button activates the Adjust Sun & Sky Background dialog box. Here you can change properties and preview the changes to the background.
