So far, your views of 3D drawings have been in parallel projection. This means that parallel lines appear parallel on your screen. Although this type of view is helpful while constructing your drawing, you will want to view your drawing in true perspective from time to time, to get a better feel for what your 3D model actually looks like.
AutoCAD provides the 3D Orbit too! to help you get the 3D view you want. You can use the 3D Orbit tool to refine your parallel projection views, but it is also the gateway to perspective views of your model. 3D Orbit has a lot of features and settings. With this in mind, you may want to begin these exercises when you know you have an hour or so to complete them all at one sitting.
If you are ready now, let’s begin!
1. Open the Setting. dwg file from the sample files off of the CD-ROM. You’ll use this file to practice using the 3D Orbit tool. This file contains a simple 3D model of some chairs, a table, and a lamp.
2.-Right-dick any toolbar and. then select 3D Orbit from the popup list. Open the View toolbar as well.
To set up your view, use the Camera tool on the View toolbar.
1; Choose the Camera tool on the View menu.
2. At the Specify new camera point: prompt, click the lower-left comer of the drawing, as shown.
3. At the Specify new camera target: prompt, click the center of the circle that appears in the middle of the drawing,.Your view changes to a side view of the chairs, as shown.
This new view is from the camera point that you specified in step 2. The view’s center is the target point you selected in step 3. Now you’re ready to use the 3D .” Orbit tool. The camera and target points you selected are at the 0 coordinate on the z-axis, so your view is aimed at the bottom of the chairs. That’s why the view is oriented toward the top of the screen.
1. , Click the 3D Orbit tool on the 3D Orbit toolbar, You can also select 3D Orbit from the Standard toolbar.
You see a circle with four smaller circles at its cardinal points. This circle is called an arc ball. It helps you control your view, along with the cursor.
2. Place the cursor on the small circle at the top of the arc ball. The cursor changes its appearance to a vertically elongated ellipse:
3. Click and drag the cursor downward from the top circle of the arc ball but don’t let go yet. The view follows your cursor and the motion is restrained in to a vertical one. When you’ve got a view similar. Release the mouse button.
When you click and drag the circle at the top or bottom of the arc ball, your view rotates about the target point you selected in step 3 of the first exercise. You can relocate the rotation point by using the Camera tool to select a new target point.
Now let’s continue by rotating the view sideways.
1. Place the cursor on the circle on the left side of the arc ball. Notice that this time, the cursor changes to look like a ellipse that is elongated horizontally.
2. Click and drag the cursor to the left from this circle on the arc ball, but don’t let go. The view now rotates about the target point from left to right.
3. Position your view so it looks like Figure 16.40,then release the mouse.
By now, you should have a feel for the way the arc ball works. You click and drag until you get the view you want. But right now, the view is not exactly right. You’ll want to rotate the view to straighten it out.
1. Move the cursor to the outside of the arc ball. Notice that it now looks like a circle.
2. With the cursor outside of the arc ball. click and drag downward. The view rotates in the direction that you move the cursor.
3. Adjust the view until it looks similar tn the one.
When the cursor appears as a circle, you can rotate the view in the view plane. This allows you to “straighten” your view once you’ve moved your viewpoint or camera location.
You’ve tried nearly all of the arc ball options. There’s one more option that is a combination of the top and side circles.
1. . Place the cursor inside the arc ball. The cursor now looks like two superimposed ellipses.
2. Click and drag the cursor and move it in a slight circular motion. Notice how the view pivots in all directions about the target point.
3. Return the view to the one shown.
This last option gives you a bit more freedom to move the view, though it can be a bit unwieldy.
Turning on a Perspective View
The view is still a bit !Ugh in the AutoCAD window. You will want to move it downward to include more of the lamp and the chair at the top. You’re also still viewing your drawing in a parallel projection mode. In the next exercise, you’ll switch to a perspective view, ‘then use the Pan tool to center your view.
1. Right-click and select Projection >- Perspective from the popup menu. Your view changes to a perspective one. The view is a bit high so you’ll want to use . the 3D Orbit Pan tool to center your view.
2. Right-click and select 3D Pan from the popup menu. You can also select Pan from the 3D Orbit toolbar, The arc ball disappears and the cursor turns into the familiar Pan cursor.
3. Click and drop the view downward to center the table top in the view. Your ,view should look like.
You saw several things happen in this brief exercise. First, you saw how easy it Will to obtain a perspective view. You were also introduced to the 30 Orbit popup t1\~nu\ This menu offers a few options that don’t appear on the 3D Orbit toolbar. You also used the 3D Pan tool on the 3D Orbit toolbar.
The 3D Pan tool on the 3D Orbit toolbar works just like the standard Pan tool you’ve been using all along, but there is a difference. You may have noticed that when you panned your view, the perspective changed as you panned. The effect is similar to that of looking out of a car’s side window as you move down the highway. When you pan your view using the 3D Pan tool on the 3D Orbit toolbar, you are moving both the camera viewpoint and the target point together. This maintains your camera and target orientation while moving the overall scene.
Using Some Visual Aids
You’re still in 3D Orbit mode, even though you don’t see the arc ball anymore. This can be a bit confusing. You can use a visual aid to remind yourself that 3D Orbit is still active.
1. Right-click and then select Visual Aids > Compass from the popup menu. The 3D Orbit Compass appears.
2•. Right-click again and select Visual Aids> Grid. A grid appears at the o z-coordinate.
3:· To help visualize the forms of the objects in this scene, turn on the shade mode. Right-click and then select Shading Modes :> Hidden. You’ve already seen both the Grid and the Hidden Shade mode. shows how your, view will look after turning on the Compass, Grid, and Hidden Shade mode.
You may have noticed that the options under the Shading Modes cascading menu were the same options available from the Shade Mode toolbar. They’re offered in the 3D Orbit popup menu for easy access, in case you want to view your model with hidden lines removed.
Adjusting the Camera
The 3D Orbit arc ball lets you rotate your camera location about the target. You’ve also seen how the Pan option moves both the target and the camera to view a different part of your 3D model. All of these tools maintain the distance between the target and the camera. In the following set of exercises, you learn how to use the tools available that allow you to fine-tune your camera location and characteristics.
Start by changing the distance between the camera and target.
1. Right-click and then choose More >Adjust distance from the.popup menu. You can also choose the 3D Adjust Distance tool from the 3D Orbit toolbar .
The cursor turns into a double-headed arrow in a perspective view.
2. Click and drag the mouse downward. As you do, the view recedes as if you were backing away from the scene. You are moving the camera away from the target location.
3. Adjust your view so that it looks like.
You can adjust the camera distance from the target by clicking and dragging up or down. An upward motion brings the camera closer to the target. A downward motion moves the camera away.
At first glance, the Zoom option on the 3D Orbit toolbar appears to do the same thing as the 3D Adjust Distance option. However, the Zoom option actually has a very different effect on the display. The Zoom option has the effect of enlarging .or reducing the size of the image, but it does so by changing the field of view of the camera: This is like using a telephoto lens on a camera. You can zoom in on a scene without actually changing your position relative to the scene.
A telephoto lens does its work by changing its focal length. By increasing its focal length, you get a closer view. By decreasing the focal length, you see more of the scene. If you shorten the focal length a lot, the image begins to distort, like the image in a fish-eye lens. The Zoom option of the 3D Orbit tool works in the same way. Try the following exercise to see firsthand.
1. Right-click and select Orbit from the popup menu. The arc ball returns.
2. Click the circle on the right side of the arc ball and drag the view to the right ,so you get a side view of both the chairs.
3. Use the Arc ball to adjust your view so it looks like.
Next, you’ll temporarily leave the 3D Orbit tool to turn on a layer.
1. Right-click and then select Exit from the popup menu to exit the 3D Orbit tool.
2. Use the Layer drop-down list to locate and turn on the Wall layer. You’ll see some walls appear in the foreground.
3. Click the 3D Orbit tool in the Standard toolbar and then right-click and select Zoom. You can also select the Zoom tool from the 3D Orbit toolbar.
4. Click and drag the mouse slowly downward. As your view moves slowly away, it also begins to distort. The vertical walls start to splay outward more and more as you zoom out, as shown in the top image. You also see the 3D Orbit compass distort.
5. Bring your view back to normal by clicking and dragging the mouse upward until you have a view similar to the lower image.
In this exercise, you turned on the walls of the room and then used the Zoom option to see its affects. As you zoomed back, you were actually changing the field of view, or focal length of the camera, to that of a wide-angle lens. You can control the focal length in a more precise way by using another command outside of the 3D Orbit tool-the Dview command. The following exercise will show you how you can precisely set the focal length of the camera.
1. Right-click and then choose Exit from the popup menu.
2. Enter Dv↵↵ Z↵. Your display changes to show a crude house. This is a visual aid for the Dview command; your drawing hasn’t changed.
3. You see the Specify lens length: prompt, with the current lens focal length shown in brackets as a default.
4. Type 35↵ for a 35-mm lens focal length. Your view changes to offer a wider view of the room as shown.
5. Press↵ again to exit the Dview command.
The Dview command offers the same functions as the 3D Orbit tool, but it is much more difficult to use. However, it does offer the ability to precisely set the camera focal length. This one feature can be of great use when setting-up views of interior spaces in an architectural model.
Now, suppose you want to move the target of your view upward slightly to encompass more of the back of the room. You can accomplish this by rotating the camera. Here’s how it’s done.
1. Click the 3D Orbit tool from the Standard toolbar. Then right-click and select More >Swivel Camera. You can also click the 3D Swivel tool in the 3D Orbit toolbar. The cursor changes to a camera icon with a curved arrow.
2. Click and drag the mouse upward to view more of the back wall of the room so that it looks similar.
Using Clipping Planes to Hide Parts of Your View
The walls in the foreground obscure the current view of the interior of the room. While this may be an accurate view of your model, you may want to remove parts of your model that obstruct your view in the foreground. To do this, you can use clipping planes.
1. While in the 3D Orbit mode, right-click, and then select More» Adjust Clipping Planes. The Adjust Clipping Planes dialog box appears. It shows your model as though you were looking at it from above.
Also notice that the view of the room in the AutoCAD window changes. You see more of the room and the chairs appear to be sliced in half.
2. Right-click ~ the Adjust Clipping Planes dialog box. The popup menu that appears offers several options.
3. Make sure the Adjust Front Clipping option ships a check mark next to it; then click the screen to close the popup menu. This allows you to adjust the front clipping plane. You can also press the Adjust Front Clipping button on the dialog box toolbar.
4. Place the cursor over the horizontal line in the middle of the dialog box, then click and drag downward. The line moves downward. This line represents the location of the.front clipping plane in relation to the objects in the drawing. Notice what happens to your view in the main part of the Auto- CAD window as you move the clipping plane. The chairs become whole gain, and the lamp appears. Move the cursor up and down to the effect.
5. Move the clipping plane downward until it is just past the lamp toward the bottom of the dialog box.
6. Close the Adjust Clipping Planes dialog box. Your view should now show more of the room, as shown.
The front clipping plane is turned on as soon as you open the Adjust Clipping Planes dialog box. You can then adjust the clipping plane by moving in the dialog box. In addition, you can turn on and adjust a back clipping plane to hide objects in the back of your scene, as shown. To do this, you turn on the back clipping plane; then adjust it just as you did the front clipping plane. Two buttons control these functions in the Adjust Clipping Planes dialog box: The Adjust Back Clipping lets you adjust the location of the back clipping plane, and the Back Clipping On/Off turns the back clipping plane on or off.
A third option, the Create Slice button, lets you move both the back and front clipping planes in unison. All of these options are also on the Adjust Clipping Planes popup menu.