Surface analysis tool: Direction - Rhino Tutorial

- [Instructor] Next up, we'll check out the first of the surface analysis tools and dig deeper into this concept called direction. Many Rhino users are not even aware of this term, or what it does. We'll start off by zooming into some sample geometry down here, I've got to sphere labeled globe. One thing to be aware of, all surface and geometry in Rhino has two directions. These are represented by the ISO curves and Rhino refers to these also as U and V. But there's a third value and that's called W, also referred to as the normal. A normal is something that is perpendicular to a surface. So I've labeled this sphere as a globe to help you understand how these three terms now work together. If U and V are the latitude and longitude, then the W value would be the altitude kind of going up in a way. Now normally we don't see normals, we just assume where they are, but we can highlight these guys by selecting a piece of geometry and going over to the standard toolbar, which reveals the main toolbar and then select, Analyze Direction. These arrows pointing in one direction or the other will tell you where the surface normal is. Now for a closed object like the sphere, that means pretty much the outside. Now in many shapes, you can flip these the other way, except this is closed, so you can't. Let's show an example where we can flip them, I'm going to select this plane right here, zoom in a bit and hit the same command. So now we're seeing the normals, which a lot of times you assume going up or out, just pointing down. That's an important thing to understand. The outside really is kind of arbitrary when you're dealing with simple flat surfaces. It can be any direction you want, unless it's closed up. And you can change that by simply clicking anywhere. It's a toggle, you got two choices, one way or the other. We're up on the command line, you can click on flip. I'm going to right click to escape up the command. We'll try one more time on this flat surface, which just happens to be trimmed. Click on direction and then we see it's pretty much the same case. It's all pretty arbitrary and can change back and forth many times. Let's go ahead and look at this final shape, which most people would say, hey, the normals are going to be pointing away because it encloses a volume. However, since it's not closed, that is not the case. I like this guy, use the same directions, and they're currently pointing in which I can change. Let's go back and leave them pointing in, so I can show you the next sequence in this analysis. This is currently open. Let's go ahead and close it. Use the solid Cap Planar Holes. Now let's see what happened to those normals. They were pointing in, we've now closed it, so what happens? Well Rhino has unified them and had them point away from the center of the volume. So that's a few examples where things that are open and closed. Let's look at something a little more frequent in your modeling. We've got some surfaces here, we've got the hole, it is currently not connected to this little intake section here. I'm kind of curious which way the normals are now pointing, so I'm going to click on the direction command, those are going in the out direction, again, kind of of arbitrary. Let's click on the hole and see where those are going. I would generally call that towards the inside, so they're not really in agreement. So we just checked out how when something is closed, it unifies normals, the same thing happens with joining. So I'm going to split those two pieces we just looked at, you can hit Command or Control + J to join or little puzzle piece button. Now that those are joined, and I can verify that up here in the command line, I can now turn on the Analyze direction and those are all unified. It did pick one of the two pieces of geometry and had the other one match, but, like we've already demonstrated, we can just flip it back the other way. Since there are openings, we can keep going back and forth as much as you want. Hopefully that's pretty interesting and helps you understand how direction works in your workflow that probably doesn't come up too often except when you do Booleans. Let's take a look at these two situations. So we've got identical geometry. We have two spheres, of course we now know the normals are going outward. But, these planes above them that intersect, I've changed the normals, one on the left, normals are pointing upwards, the one on the right, normals are pointing down. So that changes the whole basis of Booleans and if you had problems with Booleans, this is probably what was happening. Okay, we're going to go to the solid tools tool bar. I'm going to select a Boolean difference and I'll try to do these the exact same way. First surface is a sphere, right click. Then we pick a plane, right click, so that's the result. You might expect it but now let's repeat this by right clicking. Pick the sphere, right click and then the plane, right click and check it out, we get the exact opposite result. It's all because of the planes normals pointing, two different directions. So if you ever get unexpected results from Boolean, this is exactly what's happening. Just stop for a moment, check the normals of anything that's not close, changing the other way. So another way to look at direction is this whole idea of inside versus outside. A closed or solid entity cannot have its normals direction facing the interior of the object because Rhino won't allow it. But, whenever you are still open, which is less than fully closed, that direction can be changed.