From the course: Sketching for Product Design and AEC

What is orthographic projection?

From the course: Sketching for Product Design and AEC

Start my 1-month free trial

What is orthographic projection?

“

- We've discussed orthographic projection quite a bit over the past few movies. I used the analogy of a box inside a box. In our case, a wooden model of a house inside a box. I emphasized that the six walls, or faces of that outer box, serve as separate projection screens onto which every vertex, line, and surface is projected at a 90 degree angle. As mentioned earlier, orthographic drawings are, for example, what a carpenter relies on to build a house, or a furniture maker uses to construct a chair, or a craftsperson needs to build a functioning push toy, or a birdhouse with an opening large enough for a bird but too small for a squirrel. You get the idea. The multi-view nature of orthographic projection results in a non-ambiguous, i.e. clear and accurate document that can be dimensioned as well as measured directly off of, much like a map. But because each view is separate, the users of an orthographic drawing must also combine them into a single view inside their head. So how do we actually create orthographic views? To create a multi-view orthographic sketch, we generally begin with one of the views, although this is not absolutely necessary. One of the strengths of this projection system is that even a single line from one view can be projected vertically or horizontally to provide useful information for another view before either view is completed. So let's use the birdhouse as an example. Notice right away that we have some good information from the front view. In fact, it looks very much like the house model. However, from that view, we don't see enough to create a mental image of the three dimensional form. We don't know, for example, how long the perch is, or if the roof has an overhang. We also don't know the depth of the overall structure or the thickness of the walls. Simply by projecting lines upwards from the vertices of the front view, I've added some critical information, concerning the width of the birdhouse to help inform the construction of the top view and to help in the overall decision making process. Now that there are projection lines, I can decide how deep I wish to make the birdhouse, and with one line to find the back or outer edge. Likewise, I can project lines up from the vertices of the perch. And with another horizontal line, I can define or determine the length of the rod the bird will perch on. I still don't know the overhang of the roof, but I can decide that now. Notice I use a dotted line to indicate what is not visible from the top view. This is called a hidden line. I want to see what the structure looks like from the side profile, so I need to project some geometry to the side view, and here's where things get interesting. The front and top view are aligned. We can see that by following the vertical projection lines, but all we have on the side view are the horizontal projection lines I just created. Specific elements of the side view, such as the overall height of the structure and the location of the perch, can be projected from the front view. But in order to determine the length, we'll need to transfer dimensions from the top view down to the side view. So how does the information get accurately projected down to the side view? Or conversely, how does the information from the side view get projected up to the top view? The answer is actually quite simple, and possibly one you're already aware of. Just consider for a moment how important information is transferred through a periscope down to a sailor in a submarine below. Or, for that matter, how the image is projected on to film or digital sensor in a single-lens reflex camera. The answer is through mirrors, and the same thing works in orthographic projection. By adding a mirror or a reflecting plane at a 45 degree angle, any vertex can be projected up, and vice versa, without distortion. We can now see that orthographic projection is actually a system or network of lines connected through direct projection or via the reflecting plane. You can think of it as a mirror sending crucial information to and from the various views to assist the designer in the sketching process. In order to truly appreciate this, let's animate a couple of simple forms, like these little wooden houses. The architectural details, like the shape and place of the dormer and chimney, are especially crucial.

Contents