You’ve been gradually building up the detail and realism in your renderings by adding light and materials. In this section, you’ll learn how using a different rendering method’ can further enhance your 3D models. Up until now, you’ve been using the standard AutoCAD rendering method. Ray Tracing can ad d interest to a rendering especially where reflective surfaces are prominent in a model. In this section you’ll use the Ray Tracing method to render your model after making a few adjustments to the glass material.
Assigning a Mirror Attribute to Glass
Glass is a complex material to model in computer renderings. The AutoCAD standard rendering method simply gives glass a transparency with some “highlight” ”i-e flection. But glass has both refractive and reflective attributes that make it difficult to model. Because Ray Tracing models the way light works it is especially well suited to rendering views that contain large areas of glass.
To demonstrate what Ray Tracing can do, you’ll use it to render the Facade model that happens to contain an office building with a typical glass exterior. You’ll start by making an adjustment to the glass material to make it appear more reflective.
1. Choose View> Render > Materials and then in the Materials dialog box highlight Glass in the list box and click the Modify button.
2. Click the Reflection radio button in the Attributes button group.
3. Click the Mirror check box in the Color button group and then click OK to close the Modify Standard Material dialog box
4. Click OK again in the Materials dialog box and then open the Render dialog box. .
5. Choose Photo Raytrace from the Rendering Type list box at the top of the dialog box.
6. Click the More Options button. The Photo Ray trace Render Options dialog box appears.
7. Set the Minimum Bias setting to .1 and the Maximum Bias setting to .2.Whenever
you change the rendering type, you must reset these settings. AutoCAD
does not automatically transfer these settings to different rendering types.
8. Click OK and then select Day from the Scene to Render list. Next click the Background button.
9. In the Background dialog box make sure the Use Background check box is checked in the Env-ironment button group; !then click the OK button. This tells AutoCAD to reflect the background image in the glass.
10. Click the Render button. Your view will look simila/to Figure 17.22.
The sky bitmap used as a background is faintly reflected in the glass of the office building. The office building has also become brighter from the reflection. Also notice the secondary reflection of the interior ceiling on the west interior wall of the office.
The brightness of the office building is a bit overwhelming so you will want to adjust the glass material to tone it down
1. Choose View >Render > Materiais. Then with the Glass material highlighted select Modify.
2. In the Modify Standard Material dialog box, make sure the Color jPattern radio button is selected. Then set the Value setting above the Color button group to .20. This helps darken the office building.
3. Click OK to close the Modify Standard Material dialog box, and then click OK in the Materials dialog box.
4. Render the scene again. Your view will look something like Figure 17.23.
You can further reduce the brightness of the office building by reducing the intensity value of the point-light source you a-dded.early in this chapter.
Getting a Sharp Accurate Shadow with Ray Tracing
In the beginning of this chapter you learned. how to use the Shadow Map method for casting shadows. Shadow maps offer the feature of allowing a soft-edge shadow in exchange for accuracy. For exterior views, you may prefer a sharper shadow. The Facade example loses some detail using the Shadow Map method in particular the grooves in the base of the building disappear. By switching to the Ray Tracing method for casting shadows, you can recover some’ of this detail.
1. Choose View l> Render > Lights. Then from the Lights list select Sun and click.Modify.
2. In the Modify Distant Light dialog box click the Shadow Options button.
3.In the Shadow Options dialog box click the Shadow Volumes/Ray Traced Shadows check box to place a check mark there.
4. Click OK in all the dialog boxes to exit them and return to the AutoCAD view.
5. Render the view using the Photo Ray Trace rendering type. Your view will look like Figure 17.24.
Notice that you can now see the rusticated base clearly. The hadows also appear sharper especially around the surface detail of the Facade model