Use ArchiCAD to Conduct a Sun Study

Feb 15, 2005 By:Kurt Ameringer Cadalyst

When creating sustainable design and green architecture, the ability to create a sun study for a specific project location is an important component. ArchiCAD has an impressive and easy-to-use tool that allows users to run an accurate sun study with automatic time intervals from any perspective in the model.

Exterior sun studies can show the shadow impact upon your site by surrounding buildings before you begin your design as well as how your project will influence the surrounding site once built. These studies can also define and verify your passive solar design long before you have the opportunity to build it.

In the interior of the virtual building, sun studies allow us to observe how far natural light penetrates inside during winter or summer. This can again define design for passive solar systems or lighting levels for office occupancy.

Creating a Sun Study
The Create Sun Study command allows you to generate an animation or series of 3D images rendered in ArchiCAD based on the selected render engine and the Sun position settings defined in your project. Your animation can be displayed immediately on the screen or saved in a number of file formats to be shown in the future.

All the rendered projections in a sun study are generated based on the current parallel projection or perspective view 3D Projection Settings dialog box (figure 1).

Figure 1. All the rendered projections in a sun study are generated based on the current parallel projection or perspective view set in the 3D Projection Settings dialog box.

You can also set the geographical data for the location of the model and Sun parameters in the Sun dialog box available by clicking the More Sun button in the Parallel Projection Settings (figure 2).

Figure 2. Specify a variety of location and date parameters in the Sun settings.

Clicking the More Sun button in either the Perspective Settings or Parallel Projection Settings dialog box gives access to the Sun subdialog box for a series of more sophisticated sunlight settings, which can be used for PhotoRenderings.

Characteristics of light can be set in the upper part of the Sun dialog box. Double-click the color box to go to the Edit Color subdialog box. The color of directional light can be set here.

• You can decide how much of the directional light is represented in nondirectional, ambient light.
• Both the color and intensity of directional light can affect the ambient light, according to the percentage specified in the Contribution to Ambient (%) field.

As opposed to directional light -- for example, the sun -- ambient light is nondirectional and can stand as a substitute for the rich reflected and interreflected light experienced in a real environment. It can brighten otherwise overshadowed surfaces. Ambient light may have its own color -- in a pink room for instance -- and its intensity may have to vary to obtain special effects in renderings.

• Its color is set through the Edit Color subdialog box. Double-click the sample color to open it.
• Its intensity can be set between 0 and 100%.

To further enhance the realism of your renderings, the atmospheric fog effect alters light in proportion to the distance from your viewpoint. You can set the color of the fog by double-clicking its sample box to access the Edit Color subdialog box. You can also set one of four levels of intensity for the effect using the radio buttons. (To achieve a typical misting effect, set the color to white, and this will fade the more distant objects. To use light decay, set the fog color to black, and this will darken the more distant objects.) Note: To apply this effect, make sure the Fog feature is activated in the PhotoRendering Settings dialog box.

For a real-time preview of your sun, ambient light and fog settings, select the Auto Preview checkbox. If you leave the box unchecked, you can still get a preview at any time by clicking the preview window.

Click the Set City button to specify a geographical location by latitude and longitude, or by specifying a major city close to your site from the scrollable list (figure 3).

Figure 3. Specify a geographical location for your sun study.

• To add a new location, type into the appropriate edit boxes its name, the exact global coordinates and the time zone of the site, then click the Add button. The new location now appears in its alphabetical position in the list.
• To delete a location, select the city name by clicking on it, then click the Clear button to remove the city from the list.

In the Sun subdialog box, you can specify the date and time of day (just below the Set City button). The +1h correction (summer time) check box lets you adjust for Daylight Savings Time.

As a result of all these specifications, you can get the exact direction readings of the sun, with an icon indicating if it is day or night.

The orientation of your floor plan is defined by setting the North direction relative to the floor plan's orientation on screen. You can drag the compass needle or type in the angle numerically, relative to the x-axis of your sheet.

If you define the sun position by defining a location with date and time, its azimuth settings will be calculated with respect to this orientation (where East is at 0.00 degrees). Note: When using surveyor's units (Preferences / Working Units), the North of the Coordinate Box will be the same as the one set here.

Once you have defined the view you wish to begin with, you may choose to Create Sun Study from the Image menu (figure 4).

Figure 4. Establishing settings in the Create Sun Study dialog box.

Beginning on the top left, choose to create the view from the 3D Window or the PhotoRendering Window. This choice determines the quality of the finished image and will render with the current settings of the selected window.

In the Date field you can define a particular day of the year for the geographical location previously set under the Sun options. You may select the month and type the day in the edit box or use the arrows to advance up or down.

Use the radio buttons in the middle left section of the dialog box to define the duration of the sun study from sunrise to sunset for the selected day or specify a portion of the day for the sun study.

Type a number in the Interval edit box or use the arrows to define the time between two frames in minute intervals. You may also choose to render all the frames of the sun study or a single or specific series of images.

In the Results section of this dialog box, you are able to define the type and quality of the output. Available options allow export to movie files, image files and export to external renders such as 3Dstudio or VRML files.

Once you have established the criteria for the rendering, simply click the Show button to have the sun study processed and immediately displayed on your screen. You may also click the Save button to save the sun study in the selected file format.

Once created, the sun study may be used to evaluate any aspects of the sun shadows as the day progresses (figure 5).

Figure 5. The completed sun study shows how light and shadow play on your design as the day progresses.

Although traditional sketches are helpful for design evaluation, they do not compare with the accuracy of the sun study capability built into ArchiCAD. It is simply easier to understand the shadow effects during the day when the Virtual Building Model is used.