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In this video, we'll take a 3D tour of the most common types of Surfacing Commands. We'll see how they can all look the same and then with minor tweaks, how they can look quite a bit different. This will help to illustrate which one type of Surface Command will work best for you in your project. I've also purposely kept the examples pretty simple, so the before and after will be much easier to see. Let's start off with the CASE A, where all the surfaces that I am going to generate will look at the same, even though we are using 5 different commands. Just for reference though, I am going to go ahead and do this one Extrude and do it Straight.
So, this is the Surface > Extrude Curve > Straight, select and then right-click to Enter. Then I am just going out to the end. Well, this won't look the same as the others, but I want to use it for reference, because the next command is Extruding (Along Curve) is very similar. So, let's find this up on the Surface menu > Extrude Curve > Along the Curve. First, you select the curves to extrude and then when you are done, you press right-click or Enter, and then you select the path curve.
So, let's zoom in and take a look. So, it has basically taken that one profile and extruded it along the curve. We'll examine that a little more closely when we finish the others. Let's now do a 1 Rail Sweep, Surface > Sweep 1 Rail. Now, this is where you have to kind of pay attention to the Command Line. It first says, "Select the rail." Then it asks you to instantly select the cross-section profiles, of which that can be more than one.
So, therefore, when you only have one, you have to Enter as soon as you are finished. So, I am going to do that by right-clicking. I am just going to accept the defaults. Now, I am going to try the 2 Rail Sweep, Surface > Sweep 2 Rails, and pick the 2 rails, one after the other. Now, note it doesn't asked me to hit Enter when I am done. So, I want you to be aware of this because it knows you selected a 2 Rail command. There are only 2 rails that can possibly select. So, the next option up, immediately, is select the cross section curves. Now, we are done.
We have to hit Enter. I'm going to Accept the defaults. A few more curves here. Let's do the Surface Loft. Note, there is no rails for this command, which makes it extremely powerful in many situations. We just have the three separate curves. So, they're Lofted together with a minimal surface they can connect them. Finally, we'll end up with this Surface from Curve Network. This is about the most powerful surfacing command in Rhino, but we are going to keep it pretty simple for this demo.
Surface > From Curve Network. I am just going to rotate my view here and select all the curves at once. Hit Enter when done. Again, there is a lot of options here. I am going to go ahead and Accept the defaults. So, let's take a look. The surfaces are all identical, but some are more complicated than the others, so that's one key difference. I want to switch the top view and show you another difference here. Ok. I'm going to zoom in.
Note, that the Extrude here on the left doesn't bank or angle the profile, whereas the Sweeps do angle or bank the profile. So, as the curve arcs, it will bend that profile with it. We'll see that more pronounced in the next examples. Let's go back to the Perspective viewport. Then look at the same group of five Surface Commands with slight modifications to each of the curves and totally different surface results. So, this would be CASE B. Now, the modification here is just noted with the number one, so not much difference.
So, let's go ahead and do the Surface > Extrude Curve > Along Curve. It looks very similar. Now, we should start getting into some variations here. I'm going to do the Sweep 1 Rail, selecting the rail first, then the cross section, right-click to Accept. And accept the defaults. Now notice on the 2 Rail Sweep, I am taking the 2 rails and moving them out of alignment.
One rail is a little bit limiting, because that profile is not going to change too much, because it's only following one rail along the bottom. 2 Rail Sweep is where you can start getting some major variations. Just go ahead and execute that command, Surface > Sweep 2 Rails. Select each rail, cross section, right-click. So, you see a much bigger difference, is that profile - we only had one - is morphed as it goes down the 2 rails as they diverge, so it is actually stretched and scaled as it goes.
Now, in the Loft situation, I have made some changes to each of the three profiles there. This one is in the center here is much taller. Let's try that command. Surface > Loft, select the curves, right-click to finish, hit OK. Notice, once again, we've got a minimum surface connecting all the profiles that were generating the surface.
Finally, we have the Surface and Curve Network, where I have made major changes to the profiles. Notice that this profile is actually going inwards this way, out for the second one and completely different for the third one. Furthermore, we have got the rails diverging quite a bit from the top to the bottom. Let's try that command, Curve > Network. Select them in order, going in the two directions.
When I'm done I am going to accept the defaults. So, it's a very powerful command that can generate very complex, or even simple forms, but from a wide variety of curves for input. I am going to zoom back out, take a look. So, in the first CASE A, I have kept all the input curves such that the resulting surface would be identical. In that slight variations, we get completely different results, in the CASE B scenario.
So, I have a handy rule, and this is how it goes. There is always two or three ways to model the same shape, sometimes four, and occasionally five. So, you should focus on which edges then need to be exact, or you can focus on a resulting surface simplicity, or you can just use whatever command you prefer. Sometimes, I'll even get totally unexpected results, and I like it better than what I was planning. So, you can then decide to change the design. The key is to remain flexible and use whatever works for you.
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