Three point perspective is probably the most challenging of all. In three-point perspective every line will eventually converge on one of three points. Three-point perspective is the most dramatic of all and can often be seen in comic books when the hero is flying over buildings or whooping butt in the alley below as the buildings tower above.
When we view an object from the top, we are most likely viewing it in three-point perspective. Most often we are able to draw this view without worrying too much about the third point, but if the object is viewed at such as angle as to make the sides appear to be oblique from side to side and top to bottom, then we must use the third point. A good example of three-point perspective is to look at a tall building from either a top view or a bottom view as shown below. Establish the corner of the building that is closest to you and draw the vertical height line. Next, establish the angles of the sides by drawing in the top and bottom guidelines. Using visual measurements, establish the bottom width of each side by placing dots on the bottom lines. Now, measure the top width of the left side only and place a dot on the guideline. Draw a vertical line downward. Now draw a line down from the top left through the bottom left and extend it down below the building. The point where the lines cross is the position of the third vanishing point.
One-point and two-point perspective techniques can be used in the same image if needed to represent different objects. Determine if an object’s face (one-point) or edge (two-point) is closest to the viewer and then use the appropriate method. Each object may also have its own vanishing points, since only aligned objects will share them.
If the corner of an object is closest to the picture plane, then three-point perspective can be used. The third vanishing point is not on the horizon line. The position where the third vanishing point is placed, either above or below the horizon line, indicates whether the viewer is looking up at the object or looking down.
Notice that in the chair illustration the picture plane does not contain the vanishing points. It is not necessary for the vanishing points to be within the picture plane for perspective to work. When creating smaller images using two or three-point perspective, the results will often appear more natural if no more than one vanishing point is in the picture plane at any given time.
An example of where this would be utilized is the view as you look up at large buildings, or look down from the fortieth floor balcony window to see the street below. The three-point perspective drawing consists of two vanishing points that are both situated on a horizon line while a third point is introduced far above or below the horizon line. Be patient when drawing objects in three-point perspective. Understand that the third vanishing point is located off the horizon line and now becomes the z-axis. All lines on the z-axis converge towards this vanishing point. Beware of forced or distorted products that occur when drawing an object outside of the vanishing point triangle.
Incline Plane: Similar to three-point perspective, incline planes are areas which slant to or away from the main perspective grid by utilizing a third vanishing point directly above one main VP.
The name varies, but the reason behind incline planes remains the same. Incline planes are used to develop believable steps, stairs and roads to name a few items. The best example of the incline plane is the roof of a house. A third vanishing point and application of the equal spacing knowledge can be used to create hills, man-made ramps and even stairs.