We can now see that orthographic projection is actually a system or network of lines connected through direct projection or via the reflecting plane. By adding a mirror or a reflecting plane at a 45 degree angle, any vertex can be projected up, and vice versa, without distortion. The answer is through mirrors, and the same thing works in orthographic projection. Or, for that matter, how the image is projected on to film or digital sensor in a single-lens reflex camera. Just consider for a moment how important information is transferred through a periscope down to a sailor in a submarine below. 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. But in order to determine the length, we'll need to transfer dimensions from the top view down to the side view. 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. 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. 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. Notice I use a dotted line to indicate what is not visible from the top view.
I still don't know the overhang of the roof, but I can decide that now. And with another horizontal line, I can define or determine the length of the rod the bird will perch on. Likewise, I can project lines up from the vertices of the perch. 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. 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. We also don't know the depth of the overall structure or the thickness of the walls. We don't know, for example, how long the perch is, or if the roof has an overhang. However, from that view, we don't see enough to create a mental image of the three dimensional form. In fact, it looks very much like the house model. Notice right away that we have some good information from the front view. So let's use the birdhouse as an example. 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 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. But because each view is separate, the users of an orthographic drawing must also combine them into a single view inside their head. clear and accurate document that can be dimensioned as well as measured directly off of, much like a map. The multi-view nature of orthographic projection results in a non-ambiguous, i.e. 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. 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. In our case, a wooden model of a house inside a box. I used the analogy of a box inside a box. We've discussed orthographic projection quite a bit over the past few movies.