In Part 1 we looked at 3D Perspective Views and 3D Orthogonal Views, but why are 2D Orthogonal Views so important?
Try this experiment:
Now, using add another cube to the Blender drawing:
The cube will be placed on top of the first. Without changing the view, move the cube until it is directly behind the first. The two cubes should look like this:
If you looked along the Y-axis (the green line) toward the first cube, would you expect that the front cube more or less obscures the rear cube? Yes or No?
Blender allows you to easily look down all three axes by using these three keys on the Numpad: for the top view along the Z-axis, for the side view along the X-axis, and for the front view along the Y-axis. This is what you will see:
By no stretch of the imagination is the second cube anywhere near being behind the first. Let’s try the Front view then:
There’s no way the second cube (the one which shows the yellow dot) is behind the first. Let’s try the Side view then:
If you answered YES to the question above then you are no doubt scratching your head by now. If you answered NO then did you think it would be so badly off?
These three views are 2D orthogonal views and they allow you to check whether what you see in the Perspective view is actually what you should be seeing. So these three views act as reality checks.
Drawing in a 2D Orthogonal View
Because of the danger of our eyes being fooled, we often draw an object in one 2D orthogonal view, move it into the correct position in a different 2D Orthogonal View, and cross-check in the third view.
Let’s see how this is done practically in Blender. Consider a simple scene. We have a bolt and a washer. We have to get the washer into position directly below the head. It looks like the washer is directly below the shaft, but we suspect that it is not. We know that if we just move the washer in this view it is going to go wrong:
The first step is to look at the two objects in one 2D Ortho view. It doesn’t really matter which. So we first choose the front view :
Well, we didn’t expect that now, did we? However, now in this view, we can begin to fix it. Select the washer and move it into the correct position. (Or, rather, into what appears to be the correct position in this front view):
Now it looks correct, but let’s make sure by looking at the side view :
It’s still not right. So, let’s move the washer to the right into position while constraining it to the Y-axis because we don’t want it to go upward . Now the reason why we work in 2D Ortho views is that for each 2D view we can only move the object in a mixture of two directions, not three. So when we move the washer to the right in this view, and not up or down because that looks OK, we can be sure that our previous movement will not be changed because in this view we cannot move the washer forward or back:
Now it must be correct? Surely?
Well, let’s check. We’ll take a look at the remaining ortho view – the Top View with the washer still selected:
And we change to transparent wireframe view with these two icons:
We can immediately see that the origin point of the washer (the yellow dot) is not exactly in the centre of the bolt. So for the third time, we move it into position. Just to check, toggle through the other two 2D Ortho views again and then . Finally, we check what it looks like in 3D perspective projection:
Here we have a classic case of non-precision for effect. This is the difference between CAD and Artistic Technical Illustration. Take a look at where the washer is situated:
Notice the slight gap between the top washer face and the lower surface of the bolt head. This would be totally unacceptable in a CAD drawing, but in an artistic illustration, this is actually a good thing because it gives us a slight shadow to differentiate the join. You can clearly see the effect in the 3D Perspective view picture above.
For a discussion on 3D perspective views vs 3D orthogonal views, click here.