Adobe CS5 has only been out for a month or so. Let's visit some of the new features in Illustrator, Adobe's leading graphic and illustration tool.
Perspective drawing is a new feature in Illustrator CS5 that let's you define a grid in 2D then map new dimension or map image against this grid. To get started simply create a new document then choose 'Perspective Grid' (shift P) from Illustrator's tool bar.
As soon as you apply perspective grid you see 2 vertical grids retreating into the page at approximately 45 degrees. Along the base of this image you will see a control line, a 'ground line' and about midway to top you see a similar guide for the horizon line.
As you play with these guides to experiment with their presentation you will see that as you raise the horizon guide the perspective changes as it would appear if you were viewing from a much higher elevation, even looking directly into say, a building. As you lower the horizon guide, the appearance is as if you were gazing up, from ground level.
As you view this grid you see identifying colors, orange on the right pane, blue on the left pane, and green on the ground. In the center, at the base of this grid structure, you see 3 control 'widgets' which allow you to shift and manipulate these grids. Simply moving any of these controls lets you move and control the angle of these different grid perspectives.
You will also notice additional control buttons which appear as diamonds. These let you define the size and appearance of the grid. On each colored pane, the diamond control on the bottom lets you define its width as you drag back into your drawing. The diamonds on top let you control their height. There is a single diamond in the center that changes the granularity of the grid as you adjust it.
Illustrator is both a visual and a precision graphic tool. The adjustment and perspectives you define with these control objects, can also be controlled by opening the perspective grid, 'define grid' menu option under the Illustrator 'View' menu. Using a combination of visual adjustment and checking the exact values defined is a good exercise on both learning to use this new feature, and developing your use of its abilities. Under this same menu option you will see other options such as display rulers to display the exact values you have defined.