The table works with the PET 2001, the Radio Shack TRS-80, and the Apple II and costs under $450. The digitizing table used in this book is made by Talos Systems and represents a good example of the state of the art for low-cost home computers. Later aĭemonstration program will be presented that will illustrate this most incredible application. This last application is called computer aided design. You can even create schematics on the screen and use the pen to move logic gates, draw wires between the gates, etc. You can trace out a polygon and have the area measure out super-accurately. You can trace the path of a trip on a map and get precise distance. With a digitizing table you can trace highly detailed drawings and have them scaled to any proportions and then echoed on the screen. This not only allows extremely accurate data to be entered but means that pen motion will be fluid and smooth. The digitizing table sends the computer over 100 coordinates per second and each coordinate can be a number from 0 to 2048. The table contains circuits that allow it to measure the position of the pen to an accuracy of 0.005 inch (127 μm)! A typical digitizing table has an active area of 11 by 11 inches (28 by 28 cm). Digitizing Tables-A digitizing table consists of a flat table surface about 15 inches by 15 inches (38 cm by 38 cm) square, with a penlike device connected to it via a cable.Further, if you wish to trace a drawing with the light pen from, say, paper to the screen of the computer you must get the drawing onto clear Mylar, tape it over the screen, and then trace it out on the screen with the pen. This means we can't expect much more than to be able to draw on the screen. The limits of resolution of the light pen are set by the resolution of the screen itself. With sufficient circuitry and software the position of the pen on the screen of the computer can be determined. Light Pens-A light pen is a small pen-sized device that contains a light-sensitive photocell in its tip and connects to the computer via a cable.Again this is time consuming but in some cases it may be adequate. If the computer offers shape tables like the Apple, the keyboard can be used to build shapes by specifying vectors instead of coordinates. Obviously this approach is very time consuming, but it has the redeeming advantage of needing no extra hardware. Keyboard Entry-The simplest method for entering graphics data is by using the keyboard and a program that lets you turn individual dots on and off or draw lines by typing in their coordinates.Today there are about three different approaches to entering graphics information in a computer: Although high screen density means increased realism, stop for a moment and ask yourself how would you get a highly detailed drawing onto the screen of a high-resolution graphics computer? The answer is not as simple as it would seem.
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