AutoCAD Tutorial : Session Two

vpoint, list, vports, pan, chprop, hide, vslide, osnap, 3dface, zoom, transparent commands, pedit, undo, erase, oops

Begin by opening your model, using the open command or the pull-down menu.

In plan view, the four rectangles you have drawn seem to present simple figures. If you view them three-dimensionally, however, they will look quite a bit different.


* To obtain a view from the southeast (assuming the x axis to be the east-west axis), with a viewing position that will give you a 45-degree angle looking downward, type vpoint and then type 1,-1,1. (Alternatively, using Release 13 you could use the VIEW pull-down menu, and select, under preset, southeast isometric.

As you can see, this isometric view makes the rectangles appear to be very irregular. They are, of course, in the sense that the corners have different elevations. You will also see that the Rect. B and Rect. D are not at the same elevation. Can you figure out why? When we copied Rect. B (a 3d polyline with each corner at a different elevation), we put its lower left corner at the elevation (z-value) of 0, but when we drew the original rectangle, we put the upper left corner at 0 elevation.

Rect. C looks very strange because its corners are at different elevations. Where are the labels? They are all drawn at an elevation of 0; so some of them look as though they are in the wrong place here. (There is a default value for elevation; that is 0 now, and it determined the elevation of the text, since we could only indicate the x- and y-values when we picked the point for the text. If you type elev or elevation, you can change that default - but please don't do that now.)


* Type list; then select the lines in Rect. B and Rect. D. Then type . You will find a new window or the text screen showing the beginning and ending points of the two lines, among other things. Note that elevations of the points show how we changed them when we copied Rect. B. (If you use list on a polyline, it will tell you the total length of the polyline and, if it is a closed polyline, the area enclosed.) To return to the drawing window, type F2.


* To see that, in plan view, the rectangles are still positioned as they were, let's divide the drawing window into two halves - AutoCAD calls them viewports. Type vports and then 2 and just (to accept splitting the screen on a vertical line). The active viewport (some commands will affect only the active viewport) is the one with the heavy border and the only one in which the mouse cursor is indicated by a crosshair. If you want to change the active viewport, you can click with the mouse in the inactive one. (If you click in the active viewport, the system will assume that you are trying to select an object. In that case, you may need to click again to finish making a selection window, or you can type control-c - escape key in R13 - to interrupt the process.)

* Select the viewport on the right, if it's not the active one, and then type plan. (The second tells the system to accept the default, which is shown in brackets. Don't worry about the choices for now.)


You will probably find that the figures are too close to the corner of the viewport; so you may want to use the pan command to shift your image so that the part you are interested in lies more nearly in the center of your drawing window. Just type pan and then pick a point and a second point to indicate the distance and direction of the pan. Experiment with this command to see how it can help you get the right part of the drawing where you want it. When you have finished, type plan again to return to the basic plan view. The command will always show you the complete drawing.


* Use the viewport containing the plan view, and select Rect. A by clicking on it with the mouse.
* Having selected Rect. A, you should now type chprop to change one or more properties of the rectangle.
* You are going to change the thickness of the lines; so you should type t and then set the new thickness to 1. Then you must type another to complete the command. (Note: Thickness does not mean what you would expect. It does not refer to the width of the line as drawn but to the height or depth of the line.)

Observe the change in Rect. A, a change which is visible only in the viewport with the 3D view. The lines for Rect. A now have thickness (in AutoCAD's terminology); furthermore, these thick lines are treated as surfaces.


* To see that these thick lines are treated as surfaces, switch to the isometric viewport and type hide in the isometric viewport. (An isometric view is a 3D view without foreshortening. It's quicker to generate and easier to move about in than a true perspective view. We will not bother with perspective views for a while.) That command shows how the model should really look with surfaces (or thick lines), but it only works on the active viewport; so you may have to change viewports and try again.

Notice what is hidden. It now looks as if Rect. A is a box with no top or bottom. For all practical purposes, it is. (But the box should hide the text and does not. I don't know why.)


* To show more clearly how surfaces and lines differ in a 3D model, there is a prepared image for you to examine on the server. (You must download the file to see it - click here to download the file in .ZIP format while you're on line. Unzip it - the zipped file is called and the unzipped one hlsurf.sld - and put it in the directory where your model is stored. If you are not on line while working on the model, you may want to go back to your networked computer to download the file. The tutorial does not depend on your seeing the image, but your understanding of 3d views may.) Type vslide and select (from the drawing directory) the file called "hlsurf." (This screen image overlays the drawing but does not replace it; when you type redraw, the model will reappear.) This drawing shows more clearly what happens when you have a fully surfaced model as opposed to a so-called wire-frame model. The wire-frame model is just that, a frame of wires that lacks surfaces so that all edges show. The surfaced model permits views as we have them in life, with some parts of the model hidden by others, because surfaces in the model are made explicit.

* Return to your model by typing redraw.


The only surfaces we have made so far are on the sides of a hollow box, Rect. A. To give the box a top, you must make an explicit surface, using the 3dface command. Since you are going to use only existing points in the model to make this surface, you can tell the system that all mouse clicks are intended to find the end of the nearest line (easier than typing endpoint before selecting the point, as we did before, when you're going to do so several times).

* Type osnap and then endpoint. (Osnap stands for object snap; this command simply allows you to select a standard part of an object - endpoint, midpoint, etc. - and have the cursor snap to it. Look in the manual to see what the other possibilities are.) Now AutoCAD will try to find the nearest end of a line any time you specify a point with the mouse. You can turn the object snap off by typing osnap and then off. (Using the object snap can cause problems when you're trying to pick a point close to another. If a new point is to be very close to an existing one, the system may also choose the existing point rather than making a new one - even if you're typing the coordinates of a new one. So it is very dangerous to work with the object snap on all the time.)


* To make the new top surface, type 3dface and then pick the four top corners of the box with the mouse, starting with any corner and working counter-clockwise. (Be sure to work on the 3D view. You can't select the top corners, as opposed to the bottom ones, in the plan view.) Hit the after selecting the fourth point and again to finish the figure; do not select the first point as first and last point. (A 3dface may have more than four corners, but the use of more than four points is tricky. Check your manual.

* Type hide again to see the results. Now the hollow box has a lid, and the hidden line drawing looks a bit different. But the text still shows! If your figure does not look correct, did you use endpoint when you made the top of the box? If not, it's not in the right place.

* Since we've finished drawing the 3D face, we need to turn off the requirement that the system find the ends of lines; if we don't, difficulties can arise, as mentioned above. So type osnap and then off.

* This is a good time to save your work. Type qsave. (If you were to quit now, you would find that, when you start up again, there would still be two viewports.

CHPROP (again)

* Since we've seen that thick lines make good surfaces, let's make the lines for Rect. B and Rect. D thick as well. Using the plan view viewport, select one edge of Rect. B and one edge of Rect. D (using the direct click method, not a window). Now change the thickness to 1 (the command is chprop, remember?).

* Now click on the other viewport and type redraw. Only part of each rectangle has thick lines. Why? Because each rectangle was constructed of lines; each line is independent and must be given a new thickness independently. Rect. A, though, was made of a polyline, and the entire polyline is one entity; so the entire polyline was made thicker when we selected one side of the rectangle. Now select the other sides of the two rectangles and make them 1 unit thick.

* Type hide again to see the results of adding these new surfaces.

One of the advantages of using a polyline is that it can be treated as a single entity; lines with multiple segments, on the other hand, are multiple entities. Polylines can be moved, rotated, colored, and altered in other ways with a single selection; lines cannot.

But polylines cannot have different elevations at different vertices. That's one thing that makes 3D polylines different. They can have a different elevation for each vertex. However, 3D polylines cannot have thickness. That's why you weren't asked to give thickness to Rect. C. That would not work. We can, however, add explicit surfaces (3D faces) to the basic rectangle with the 3dface command.

* Using either viewport (the 3D viewport is often best with complex shapes, but it can be confusing with a shape like this, one that has different elevations at the corners), find the coordinates of the northwest corner of Rect. C. To do that, type id and then, after typing endpoint, select the northwest corner of Rect. C. The system should respond with x=3.800; y=5.375; z=0.000. Using that information, we can define where the corners of our 3D face must be in order to make another box with sides one unit high. The first corner will be at 3.800,5.375,1.000 (1 unit above the corner we just located). You will need to work in the 3D viewport to make the 3dface; so be sure you understand the figure and then select the 3D viewport.

* So, type 3dface.
* Then enter the coordinates of the first point of the new surface, 3.8,5.375,1.
* Then, for the second point, type endpoint and pick the northwest corner of Rect. C.
* For the third point, type endpoint and pick the southwest corner.
* For the fourth point, type @0,0,1 (to place the last point is 1 unit above the third one). You will need another to complete the command.

Now, if you start with the correct corner, you should be able to make another 3D face for each of the other sides of Rect. C without knowing any coordinates but knowing that the last point will always be 1 unit above the third one. (Remember that typing will invoke the last command; so you needn't keep typing 3dface again and again. (Don't try to use the osnap command to avoid having to type endpoint over and over again. This is one of those figures that will cause problems. But be sure to use endpoint!) You may want to zoom in on the figure before trying to draw all these faces. If so, remember to type zp (for zoom previous) when you finish.

* Type hide again, and you will see no real differences between the thick lines and the 3D faces. Note, however, that only rectangle A has a top; the others have only sides.

* Now change to the plan viewport and draw another polyline ( pline command)
* From point 9,0,0
* To 1,0
* To 1,9, and here type arc (a would do)
* and then 9,9, for the end of the arc.
* Type close (or cl) to close the polyline.


* In the plan view you may not be able to see the entire new polyline; so type zoom .5x to make it smaller; then type pan and use the mouse to get the model where you want it. You may need to use the command more than once.


* Now use the list command; type list and then l, for last object drawn, and then again to finish choosing objects. The coordinates of the vertices, the perimeter, and the size of the area enclosed by the polyline will be displayed.

PAN, ZOOM, Transparent Commands

The pan and zoom commands are valuable viewing aids, of course, but they can also be crucial ways of letting you see the appropriate part of a model while you are making a new figure. Sometimes, though, you can be in the middle of making the entity when you realize that you need to pan or zoom. In an earlier lesson, you used the command 'z to zoom in the midst of a pline creation. That's called a transparent zoom (I don't know why they call it that either); you can also use 'p to do a transparent pan, panning in the midst of another process. (The apostrophe before a command - many commands but not all - indicates to the system that it can interrupt the current process to perform the command and then return to finish the current process. Check the manual to see what other commands can be used in this way. Note that you can use the help command in this way; in fact, typing 'help or '? will not only bring up the help screen, it will display the section pertaining to the command in progress.)


* You can edit a polyline in two ways. The easiest way is to click on it so that the "handles" show. The handles are the little blue boxes at the vertices.
* To move the southwest vertex of the last-drawn polyline, click on the handle so that it is solid-filled.
Now type @0,1. The vertex should move up one unit. (If it does not, make sure osnap is off.) When you first clicked on the handle to make it solid, the prompt stretch to point . . . showed in the command prompt area. You typed the coordinates to indicate how far to move - stretch - the point. There were some other possibilities that we will ignore for now.

* The other way to edit a polyline is to type pedit and then select the polyline with the mouse.
* Type e (edit vertex)
* and then keep typing n (for next point) until you have reached the last point in the polyline. Now type p (for previous point) and keep doing that until you get back to the first point. Using this system, you can select any point to change.
* Type m (for move) and type@0,1. Type x twice and you will have finished the command.

*You can also add a new vertex to a polyline with the pedit command. Type pedit and then select the polyline with the mouse.
* Type e (edit vertex)
* and then type i (for insert). You should now select the location of the point you want to insert; it will be the point after the first one in the polyline (assuming you did not move to another point before starting to insert the new point).
* To locate the point, type mid (for middle) and select the line that makes the bottom of Rect. D. Your new point will be in the middle of that line. * Type x twice and you will have finished the command.


*Since we don't want the point you just inserted to remain in the model, type undo.

You will be prompted for a response, with number being the default. The number you type will be taken to be the number of command operations to undo. Typing will be taken to indicate the last command only (equivalent to 1). So type a to undo the editing of the polyline.

* To erase the polyline, either type erase and select the polyline, or select the polyline and type erase.

Erase the polyline using one of the methods just described. Having done that, however, you have changed your mind

* so type oops.

Oops differs from undo, because it is intended only to change the last command, and it applies only to a small group of commands, including erase. Undo is a far more flexible command.

Save your work by typing qsave.

Then make slides of your current work. You will need two slides, because each viewport must be treated independently. Select one viewport, type mslide, then give your slide a name. Then switch viewports and repeat the process.

Now return to a single viewport using the vports command. Make sure you have a plan view showing.

Time to stop.

Type end.

End of Session Two

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