3D AutoCAD 2004/2005: One Step at a Time

24.1 Two Types of Graphics

Two categories of graphic files are associated with AutoCAD: Vector Images and Raster Images.

• Vector Images

  By default, AutoCAD creates vector images. In fact, you've been drawing vector images since you began using AutoCAD.

  Vector images locate geometry by definition and coordinate. For example, a line has two defined endpoints. AutoCAD treats it as a single object – a line – by definition.

  Vector images hold their definition regardless of the resolution of the screen or drawing view. Since they only have to define coordinates and objects, their size is quite small compared to a raster image of the same objects.

  Types of files found in this category include:

  • .dwg – You're already familiar with how AutoCAD shares its drawing files within the AutoCAD program (blocks and Xrefs).

  • .3ds – This is another Autodesk file.

    This one works with 3D Studio.

  • .dxf – ASCII version of the image file.

  • .sat – The ACIS file format.

  • .eps – Adobe graphic file. Useful for sharing information with Adobe's publishing applications.

  • .wmf – Windows MetaFiles were created by Microsoft for use in its graphics programs. You can use them to share information with most Microsoft publishing software. (Note: A .wmf file actually contains both vector and raster imaging.)

• Raster Images

  Most non-CAD programs use raster images. These images locate geometry by screen pixel coordinate. In other words, objects aren't defined as circles, lines, and so forth but are the result of the color definition of a series of pixels.

  This method of graphics creation generally requires more memory and tends to lose image quality (sharpness) as the viewer gets close to the image.

  The more popular types of files in this category include:

  • .gif – An ideal Internet file because of its small size, the .gif file also works well for AutoCAD drawings. It is, however, limited to 256 colors, making it great for logos and cartoon-type images but of little use for photographs.

  • .jpg – Also good for Internet use, the .jpg (pronounced "jay'-peg") file doesn't have the .gif's color limitations, making it perfect for photographs. However, the .jpg file can become quite large.

  • .tif – Microsoft had a hand in developing this file type, so its acceptability in various graphics programs is almost universal.

  • .bmp – Microsoft's original bitmap, this file type also is almost universal in acceptability. Virtually all IBM-type computers (all those with the Windows operating system) use .bmps in the Windows' Paint program.

  • .pct – Use this Apple graphics file for easy exchange with the Apple-type computer.

Other and lesser-known file types include .rle, .dib, .rst, .gp4, .mil, .cal, .cg4, .flc, .fli, .bil, .ig4, .igs, .pcx, .pct, .png, .rlc, and .tga.

Since we're already familiar with the important vector images, let's look at raster images.