You’ve already seen how you can assign a material to an object by adding the granite pebbles and glass materials to the buildings in the Facade3. dwgfile. Many of these materials make use of bitmap image files to simulate textures. You can create your own surface textures or use bitmaps in other ways to help enhance your rendering. For example you can include a photograph of existing buildings that may exist within the scene you are rendering.
Figure 17.25 shows a bitmap image that was scanned into the computer and edited using a popular paint program.Now imagine that this building is across the street from the Facade model and you want to include it in the scene to show its relationship to your building.
The following exercise will show you how it’s done.
1. Click Redraw on the Standard toolbar and then adjust your view so it looks like the top image of Figure 17.26.
2.Draw a line-133 feet long, as shown in the top image of Figure 17.26.
3.Change the thickness of the line to 80′ using the Properties tool.
4. Choose View> Render> Materials. Then in the Materials dialog box click New. Notice that the New Standard Material dialog box is the same as the dialog box for the Glass material. The settings are not the same however.
5. Enter Build 1 for the material name.
6. Make sure the Color IPattem radio button is selected, and then click the Find
File button in the lower-right comer of the dialog box.
7. Click the List Files of Type drop-down list. Notice that you have several file
types from which to choose.
8. Choose GIF from the list and then locate the Market 2. gif file. This file comes with the other sample files on the companion CD-ROM.
9. Choose Open to exit this dialog box. Then click OK in the New Standard Material dialog box.
10. In the Materials dialog box make sure Build l is selected in the Materials list and then click the Attach-e button.
11. Select the line yoti added in step 2, and then press .
12. Click OK to exit the Materials dialog box and then render the scene. Your view will look like the bottom image of Figure 17.26.
The bitmap image does not appear properly in the rendered view. Instead it looks like a vertical streak of colors. When you see this streaking you know your bitmap image or material is not properly aligned with the object to which it is attached. The following exercise introduces you to the tools you need to properly align a bitmap image to an object.
1. Redraw the-screen. Then choose View ~ Render > Mapping or click Mapping on the Render toolbar.
2. At the Select objects: prompt select the extruded line you created in the last exercise. The Mapping dialog box appears .
3. Click the Adjust Coordinates button. The Adjust Planar Coordinates dialog box appears.
Notice the rectangle in the area labeled Center Position. This shows the relationship of the bitmap image to the object to which it has been assigned. All you can see is a vertical line.
4. Click the WCS YZ Plane radio button. The plane defined by the Y: and z-axes is parallel to the surface on which you want the bitmap to appear.
5. Click the Preview button. Now you can see how the bitmap will appear on the vertical surface. You now need to adjust the positioning of the bitmap.
6. First you want to increase the size of the bitmap in relation to the surface so the image of the building completely covers the surface. To do this you need one other dialog box. Click the Adjust Bitmap button. The Adjust Object Bitmap Placement dialog box appears (see the top image of Figure 17.27).
7. Enter .95 in the Scale input box to the left of the U, and then enter .76 in the Scale input box to the left of the V.The U is the horizontal direction scale and the V is the vertical direction scale.
8. Click the Preview button to view the effect of the scaling. Notice that the image is larger but still not centered vertically .
9. Use the vertical Offset sliders to move the outer rectangle in the graphic. upward so it looks like the bottom image of Figure 17.27 and then click the Preview button again. Now the image fits within the rectangle.
10. Click OK in each of the dialog boxes to close them, and then render the model. Your view will look like Figure 17.28.
Notice that the image of the building across the street now appears correctly and no longer looks like vertical streaks. Neither are there any odd blank spaces on the building. As you have seen in the previous exercise the Adjust Object Bitmap Placement dialog box allows you to stretch the image vertically or horizontally in case the image is distorted and needs to be fitted to an accurately drawn object.
Another option is to use a paint program to refine the bitmap image before it is used in AutoCAD. AutoCAD attempts to place the bitmap accurately on a surface so if the bitmap is fairly clean and doesn’t have any extra blank space around the edges you can u~”ally place it on an object without having to make any adjustments other than its orientation.