Doing Fast Perspective Setups in the Field

Part 5: Tips and tricks

And now, a few helpful facts. To find the center of a rectangle, you can draw an x from corner to corner. This also works if the rectangle is in perspective. This is how you find the perspective center of a rectangular object.

You can extend this fact to place a series of regularly spaced objects, such as telephone poles, out to the horizon, in perspective. 

To freehand an ellipse, start by drawing the perspective rectangle that bounds the ellipse. Then draw an x to find the perspective center of the rectangle, and draw a plus through the center. Mark each arm of the x about a third of the way in from the edge, and now you have all the points you need to freehand the ellipse. This is a very useful technique for drawing things like car tires.

Figures of equal height will intersect the horizon line at the same point on their bodies. So if the horizon line is at head level, it will intersect the heads of all the figures in the picture that are the same height as the viewer. This will remain true no matter how close or how far away they are. You can use this fact to hang the figures onto the horizon.

If a taller figure is N heads taller than the horizon, this will remain true no matter where in space the figure is. If a shorter figure is N heads shorter than the horizon, this also will remain true no matter where in space the figure is.

To prevent scale problems, you should select one vertical line somewhere in the drawing and designate that as you're measuring line. All measurements should be made on this line, and projected forward or back in space, using perspective. For example, if you're measuring line is a doorjamb, you could conjecture that the height of an average man will be about ¾ the height of the doorjamb. This will allow you to keep all the objects in the drawing on the same scale, no matter where they are in three dimensional space.  Draw a line from the vanishing point, through the height marking on the door jamb, and another one through the bottom of the door jamb, where it meets the ground. This will allow you to project the measurement anywhere in 3-D space.

That about wraps it up for fast perspective set-ups. There's a lot more to say about perspective, but many thick books have been written about it, so I won't repeat them here. This is just a guide to the particular tricks I find most useful for urban sketching. See you in the field...

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