AutoCAD Backstage by Wm W Wells

Appendix B: Digitizers


      1. Setting up a Digitizer
        1. CADvise: know it all
        2. AutoCAD technique: tablet setup
      2. Digitizing Old Drawings
      3. Creating a Second Configuration

Appendix A. AutoCAD Backstage home. AutoCAD Backstage Index. Appendix C.

Setting up a Digitizer:

The digitizer tablet menu requires special setup. If you buy your computor system through an AutoCAD dealer, the dealer should help you with the setup. Even though the digitizer is not a necessary piece of hardware for current releases of AutoCAD, some drafters still prefer the digitizer menus to the onscreen menus. This is for you.

AutoCAD comes with a default tablet menu as a part of the standard AutoCAD menu file. Somewhere in your box of manuals you should find a plastic or cardboard menu that you tape to your digitizer. Tape it somewhere that is comfortable to reach. Then you must tell AutoCAD where to find the menu and drawing area on the tablet. The standard AutoCAD tablet menu has 25 columns by 25 rows broken up into four menu areas and one drawing area. There are other custom tablets available and you can change this one, (see my chapter on Advanced AutoCAD), but I suggest that you get used to this one first, and add to it when you are ready.

Another way of releaving wrist stress is to move the tablet menu once in a while. A colleague of mine was assured by his advanced AutoCAD instructor that it would take four hours to do, so I timed myself. It took one minute. AutoCAD is very big and complex. Few people can claim total mastery of the program, so if you get an unsatisfactory answer to an important question, get a second opinion.

CADvise :
Nobody knows it all, get a second opinion.

To locate the tablet menu on the digitizer, type [TABLET] and press enter. Type [CFG] for configure and press enter. AutoCAD will direct you as follows:

AutoCAD Technique: Tablet Configure Command

Enter the number of tablet menus desired [1-4] <4>:
	[Accept the default <4>]
Do you want to realign the tablet menu areas? <N>:
	[Answer YES]

Digitize upper left corner of menu area 1:
	[pick the upper left corner of the top printed
	menu area, the corner is marked with a circle]
Digitize lower left corner of menu area 1:
	[pick the corner]
Digitize lower right corner of menu area 1:
	[pick the corner]
Enter the number of columns for menu area 1:
	[25]
Enter the number of rows for menu area 1:
	[9]

Digitize upper left corner of menu area 2:
	[pick the upper left corner of the middle left
		printed menu area]
Digitize lower left corner of menu area 2:
	[pick the corner]
Digitize lower right corner of menu area 2:
	[pick the corner]
Enter the number of columns for menu area 2:
	[11]
Enter the number of rows for menu area 2:
	[9]

Digitize upper left corner of menu area 3:
	[pick the upper left corner of the middle
		right printed menu area]
Digitize lower left corner of menu area 3:
	[pick the corner]
Digitize lower right corner of menu area 3:
	[pick the corner]
Enter the number of columns for menu area 3:
	[9]
Enter the number of rows for menu area 3:
	[11]

Digitize upper left corner of menu area 4:
	[pick the upper left corner of the bottom
	printed menu area]
Digitize lower left corner of menu area 4:
	[pick the corner]
Digitize lower right corner of menu area 4:
	[pick the corner]
Enter the number of columns:
	[25]

Enter the number of rows:
	[7]

Do you want to respecify the screen pointing area? <N>:
	[Yes]

Digitize lower left corner of screen pointing area:
	[pick corner]
Digitize upper right corner of screen pointing area:
	[pick corner]

That's it, you are done. If AutoCAD balks when you try to pick a corner, make sure that you have placed the tablet menu completely in the active area of the digitizer. The digitizer's active area is that portion of the tablet that is reading the signal from the puck. On many digitizers the power light will glow steadily until the puck's target passes out of the active area. The power light will begin to flash when the puck is out of the active area. This may be several inches from the side of the tablet.

Menu area 3 may seem strange. When you look at the printed menu there appear to be three pick columns and a blank column, or four columns. Actually the three columns on the tablet menu have been constructed of nine columns in the menu file. The blank column occupies three file columns and the three pick columns occupy two file columns each. That is why you have to tell AutoCAD that there are nine columns. If the drivers are all loaded properly and the menus are all in the active area, everything should be working properly. Try picking a command off the digitizer tablet menu. The command should type itself. This saves time shifting from keyboard to tablet and back again, and you will not have to remember what to type. Starting with Release 12, the on screen toolbox makes the tablet menu less important. The screen pointing area is your drawing area. The restricted drawing area requires less arm movement to draw a line.

Now is a good time to get out the AutoCAD tutorial in your manuals and get familiar with simple drawing techniques. Draw lines, arcs and circles. Get used to using the drawing coordinates. Place drawing elements on separate layers and get used to turning them on and off. Practice editing the drawing elements using mirror, copy, stretch, array, scale, etc. Get comfortable with using text styles and editing text. The tutorial also introduces blocks, hatches, dimensions, paperspace and printing or plotting.

chapter index.

Digitizing Old Drawings:

Generally digitizing is cheaper than scanning, and can be just as fast. Digitizing is also time consuming. Large drawings are difficult to digitize on a small digitizer. If you have much digitizing to do, get a big digitizer. Normally your tablet will be set up with tablet menus and a small drawing area. To digitize you will have to shut off the tablet menus using the TABLET command and CALIBRATE the digitizer. If the drawing or portion of a drawing that you wish to digitize is larger than the digitizer's active area you will have to create a match line.

To calibrate, you must locate two or three points on the drawing for which you know the coordinates in space. If the drawing is a ground plan, place the first point where the center line and the plaster line cross. That point will almost always be 0,0 (see the chapter on Ground Plans). The second point should be a good distance away for accuracy's sake. The back wall where the center line meets it is often a good choice on a ground plan. If you know that the back wall is 50'0" up stage, gently make a small pencil mark and write 0,50'0" on the drawing. These two points define a calibration line. This line could also serve as match line between the left and right halves of the stage house. A third point is useful if there is concern that the drawing might have stretched in one direction. Select the third point a good distance away at a right angle from the other two.

Tape the drawing down to the digitizer. If the drawing is small enough to fit in the active area of the digitizer, (see the section on Setting Up to Draw, above), tape it down so it fits. Do not be concerned with the title block and border on the drawing as yet.

To CALIBRATE the digitizer for digitizing, open a new drawing in AutoCAD. Type [TABLET] and press enter. Type [CAL] and press enter. AutoCAD will ask you to select the first point for digitizing. Carefully locate the puck's crosshairs over the first point and pick that point. You will be asked for the coordinates of that point. Type in the coordinates. In the example above you would pick the meeting of the plaster line and the center line. Type in [0,0] for coordinates. AutoCAD will now ask you to select a second point. Again carefully pick the other end of the calibration line. You will be asked for coordinates for the second point. Type in coordinates for the second point. In the above example, pick the point where the back wall and the center line meet. The coordinates would be [0,50'0"]. You will be asked to locate the third point. If you have one selected on the drawing, repeat the process for that point. Otherwise, press enter.

If the portion of the drawing that you wish to digitize is too large to fit in the active area, you will have to digitize one portion at a time. Create a match line in the middle of the portion of the drawing that you wish to digitize. Tape the drawing to the tablet with the match line placed to one side of the active area. Calibrate the tablet using that lines end points. When you finish digitizing that side of the drawing, pull up the drawing and move it so the match line is near the opposite edge of the active area. The remaining portion of the drawing should be in the active area of the digitizer, ready for digitizing. Repeat the calibration procedure with the match line in its new location. Digitize the rest of the drawing.

If you have picked the same points and supplied the same coordinates, the elements of both sides of the drawing should appear correct relative to the match line. Two factors play havoc with digitizing, inaccurate blueprints and sloppy digitizing. The first is the old problem of trying to make a silk purse out of a sow's ear. If the information you have says the back wall is back so many feet, but the drawing actually scales out to something different, how much can you trust the original drawing? If the walls on the drawing are not at right angles, are they drawn that way intentionally or by mistake, or has the blueprint stretched?

The smaller and fussier the original drawing the more difficult it will be to accurately pick points off the drawing. When doing a groundplan, put SNAP mode on. Set the SNAP aspect to the assumed accuracy of the original drawing. I generally digitize a groundplan to the nearest 1/2" or 1". This will also help get walls that are almost straight on the print, straightened in the digitized drawing. If you have been given exact coordinates of certain elements, use those coordinate to enter the elements. Then double check the location against the actual drawing. Place the puck crosshairs over the element. The cursor should line up with the typed coordinates. If not, check the drawing with a scale rule.

Avoid using SKETCH to trace out irregular shapes. Sketch can create a lot of tiny lines which fill the memory. Instead, use lines and arcs. Alternatively, use sketch to capture the shape, and then replace small lines with longer lines and arcs wherever possible.

As the puck moves across the taped down drawing, it passes its relative location to AutoCAD. Neither AutoCAD, nor the digitizer are concerned with what the actual scale of the drawing is. You can be digitizing feet and inches from a metric drawing. If the drawing that you are digitizing is a fax or Xerox, the scale may be a mystery. As long as you know the location of two points on that drawing in AutoCAD's current drawing units, and as long as the scale is consistent across the drawing (a definite maybe, maybe not, for a fax or Xerox), AutoCAD will translate those coordinates to the drawing units that you have established.

AutoCAD also does not care which direction you tape down your drawing. If you tape it upside down, but enter the coordinates correctly, the puck will be moving down the digitizer while the crosshairs are moving up the screen. In the example of the groundplan above, you might have confused the XY coordinates and entered the second point as [50'0", 0]. Now when you move the puck towards the center of the back wall, the screen crosshairs will be moving to stage left. You will have to re-calibrate.

If the drawing moves, or if you remove it and put it back, you will have to re-calibrate. The digitizer does not know that the drawing has moved, it only knows where the drawing should to be.

If the drawing fits the digitizer better sideways, but is hard to follow when the puck and screen crosshairs are moving at right angles to each other, change the viewpoint in AutoCAD. Type [VPOINT]. Your starting viewpoint is 0,0,1. To rotate 90, enter [-1,0,1] at the prompt. See if the puck and crosshairs are in sync. If the screen crosshairs are moving in the exact opposite direction, type in [VPOINT] again. Now enter [1,0,1] in answer to the prompt. By now, they should be in agreement. When you finish digitizing and want to get back to the normal strait up view of the drawing, type [PLAN] and press enter. I will cover viewpoint more completely in the chapter on 3D drafting.

chapter index.

Creating a Second Configuration:

If you are likely to be digitizing sometimes and working off the tablet menu at others, you will not want to be recalibrating your tablet menus continually. Create two configuration files, one for digitizing and one for normal drawing in the tablet menu.

Create a new directory called DIG in the root directory for the new configuration file.

If you are working in AutoCAD for Windows, copy the ACAD.INI and ACAD.CFG files to the new directory DIG. Open the AutoCAD workgroup. Do not open AutoCAD. Press Control and click on the AutoCAD program-item icon. Drag it to the side with control still pressed, then release. This should create another copy of the AutoCAD program-item icon. The title bar of the copy should be highlighted. From the Files pull-down menu, select Properties. A Dialogue box will come up. This will allow you to edit the new icon. For Description, type in Digitize. This is the name that will come up under the program-item icon. The Command Line entry calls the AutoCAD execute file, usually [C:\ACADWIN\acad.exe]. To the end of this line add a space and type [ /C C:\DIG]. This tells AutoCAD to find the configuration files in the DIG directory located in the root directory of the C drive. You may now enter a new Working Directory and use Change Icon to get a selection of icons to choose a new icon. This is not a good command for a Shortcut Key command so leave that blank. Click OK. The new icon should now say Digitizer in its title bar. Either icon will open AutoCAD, but each has a separate configuration and setup file. One program item icon accesses one configuration and set of preferences, and the other accesses the other set.

The original icon will have the tablet configured for tablet menus, while the copy is configured for digitizing. Each can be set with different screen preferences, as well. You will still have to recalibrate whenever you prepare to digitize, but you will not loose your tablet configuration in the process.

To load a separate configuration of AutoCAD for DOS, you must create a batch file. In a simple text editor, such as DOS's own Edlin, make a new file called DIG.BAT.

chapter index.

Appendix A. AutoCAD Backstage home. AutoCAD Backstage Index. Appendix C.

Copyright © 1999 Wm W Wells. All rights reserved.