Converting AutoCAD Drawings

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AutoCAD elevations are line drawings that often include line thickness (called line weight in AutoCAD) as another graphical dimension. Traditionally, elevations convey the outlines of a structure's major features, and line weight emphasizes depth and the relative importance of the objects shown.

Elevation layers in AutoCAD are usually numbered sequentially (Elev-1, Elev-2, and so on), thus identifying their line thickness; for example, progressive layer numbers might refer to thinner lines. In contrast, plan layers refer to the building systems to which the lines belong (for example, the layer A-wall represents an architectural wall).

Line thickness information is not needed when you convert AutoCAD drawings, because you will be illustrating the elevation's depth with more expressive tools available in Photoshop: texture, shadow, and reflection. Therefore, there is usually no benefit in preserving the layer structure with elevations when converting CAD drawings to images as you did in the previous chapter.

In the following steps, you will convert the entire elevation drawing from the CD as a single image. Later in this chapter, you'll see how you can reimport additional information from CAD once your Photoshop project is underway.

1. Launch AutoCAD and open the file Elevation.dwg from the Chapter 6 folder on the companion CD (see Figure 6.1).

Figure 6.1

Elevation line drawing in AutoCAD

Figure 6.1

Elevation line drawing in AutoCAD

Autocad Elevation Designs Dwg

NOTE I'm using AutoCAD 2005 in this book, but the .dwg files on the CD are stored in AutoCAD 2000 format for backward compatibility.

2. One the Command line, type LAYER and press Enter. The Layer Properties Manager dialog box (see Figure 6.2) shows how this drawing's layers are organized: numerical layer names range from Elev-1 through Elev-7 (plus layer 0), and each layer has a different line-weight setting. Click the Cancel button; this step was for your information only.

Figure 6.2

The Layer Properties Manager dialog box

Figure 6.2

The Layer Properties Manager dialog box

TIP The sample elevation CAD drawing has already been cleaned. See Chapter 5, "Presenting Plans," if you are referring to this tutorial but working on your own elevation drawing.

To convert this AutoCAD file to an image, you will use the printer driver, plot style table, and custom paper size that were set up in Chapter 5. If you haven't performed these steps, skip ahead to step 5 and open an already-converted image from the CD.

3. Choose File > Plot or press Ctrl+P to open the Plot dialog box, as shown in Figure 6.3. Click OK if you see a warning dialog about a driver and plot device.

Figure 6.3

Plotting with the Image-Printer in AutoCAD

Figure 6.3

Plotting with the Image-Printer in AutoCAD

4. Select ImagePrinter.pc3 from the Name drop-down list box in the Printer/Plotter group. Next, select ImageSize from the Paper Size drop-down list box. Click the More Options arrow button if necessary, and choose Images.ctb from the Plot Style Table drop-down list box. In the Plot Area group, select Extents from What To Plot drop-down list box; check Center The Plot. Change the plot scale to 4 pixels = 1 unit. Click the Portrait radio button in the Drawing Orientation group. Click OK, and save the image file as Elevation-Model.tif in the Browse for Plot File dialog box that appears.

5. Close AutoCAD without saving the file, and then launch Photoshop. In Photoshop, open the file Elevation-Model.tif that you saved in the preceding step. If you skipped that step, you can open this file from the companion CD.

6. The AutoCAD ImagePrinter outputs a bitmap image (white and black pixels only, see Chapter 1, "The Basics"). Because you can't convert directly from bitmap to RGB color mode, you must convert this image first to grayscale and then to RGB. Choose Image > Mode > Grayscale to open the Grayscale dialog box. Set a size ratio of 1 and click OK. Next, choose Image > Mode > RGB Color to change color modes.

TIP Switch to 50% or 100% magnification; press Ctrl++ or Ctrl+- to zoom in or out so that the image fills your screen as much as possible. The line work looks best when the magnification is either halved or doubled from the actual pixel size (12.5%, 25%, 50%, 100%, 200%, and so on). Intermediate magnifications (16.7%, 33.3%, 66.7%) suffer from partial resampling that causes some of the line work to appear to be missing.

7. An uneven border surrounds the elevation because the rectangular building was plotted on a square image size in AutoCAD. Automatically crop the excess border with the Trim command: choose Image > Trim to open the Trim dialog box. Click the Top Left Pixel Color radio button and click OK.

8. Now that the image is trimmed to the edges of the actual line work, we can add an even border back to the image using the Canvas Size dialog box. Type D to ensure that the default colors are set. Choose Image > Canvas Size to open the Canvas Size dialog box, as shown in Figure 6.4. Check Relative in the New Size group, and then change the measurement drop-down list boxes to inches if they're not already. Type 5 in both Width and Height text boxes and click OK. The background color was automatically used to color the added canvas (white in this case).

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