Join Veejay Gahir for an in-depth discussion in this video Create curves on a surface, part of Alias Essential Training.
- Let's take a look at how to create a curve on a surface. We've looked at similar commands in the past and those were creating what we call a curve on surface. This is actually curve data on the surface. We're gonna move over to this example here. What we have is essentially, we have a surface with the lettering "Alias" behind it. Let's go to wireframe. We're going to, just very quickly I'm going to add a little bit of the patch precision lines so you can see the complexity of that surface.
That surface actually is quite a complex surface to project and create curves on top of. Let's go to the Surface Edit, Create CurveOnSurface, Project, and you can see from the example here this is what we've been using in the past which was Curves on surfaces. We're actually gonna select Curves. If we do a reset we're gonna go back to Curve on surface by default but check on Curves. What we're gonna do is we're gonna use Curve fit. You'll see the difference between Curve fit and Match original is that I have the ability with Curve fit to use explicit control.
I always like this because it gives me full control over the complexity of the end result. We're gonna select the Curve fit option and we're gonna project in the Y direction. I can tell that because my green arrow down the bottom here is my Y vector, and that's the direction I wanna project in. Let's go ahead, select the surface, space bar. And let's just window over the letter "A" and then space bar. The default when we use explicit control always goes back to one-to-one.
This is quite a complex command, there's a lot of number crunching going on in the background so Alias always starts you off with a very simple degree one, single span. That way it avoids any potential for the system to lock up with a complex project. We can see from this here that we are 9.5 millimeters distance at this point here. What we're doing is we have basically a straight line, and we're trying to project a straight line onto a curved surface. Obviously we're gonna have quite a lot of error. The thing to do here now is again, very gradually increase the degree, one at a time here.
Now we've dropped down to 0.026 in that particular area. We just scan over the whole result. That's not too bad but we could go up to a degree three. And that's much better. When would we jump into increasing the spans? When you get to degree three or four make sure that you get to that level at least, on the degree before you start increasing spans. There's no point increasing spans when you're at, let's say a degree two. With three or four, if that wasn't accurate enough then I would increase the span, let's say to maybe two.
So far this is giving us a great result and I'm quite happy with that. If I go to Match original you'll notice we've jumped back to a pretty poor result here. Match original uses the complexity of the original data, holds that complexity and tries to the do the best projection that it can. If we delete this data and we select the "A" ... And let's just light up the CV hull. You can see that essentially they are straight lines so we don't have a lot of flexibility in that lettering to be able to project onto a curved surface and get an accurate result.
We'll take the CV hulls off and let's go ahead and do the command again. We're gonna do Project, Create Curves and this time we're gonna say Fit curve. Again, make sure that you've got the right vector set because this time, what I'm gonna do is select the surface, space bar, and select over all of the lettering Alias. If I've got the wrong projection and I've got the wrong value of degree or span from my previous command this could take a long time. Space bar to project. That took a while to do, it took about a minute.
And again it depends on the power that you have within your processing chip on your computer and also exactly what we're asking Alias to do. This is quite a jumbled mess here but you can actually go in there and just quickly scan over. I try to decipher any areas that are out of tolerance or greater tolerance than you are willing to accept. In this case this is gonna work for us. I'm gonna say ... Let's come out of the command and press L to delete those locators. Now let's just select over everything to tidy this up.
You'll notice now I'm gonna switch off CV hulls. Here's a point to note: If you select entities that the CVs are active on and you select entities that the CVs are not active on, for example the lettering at the back here, this comes back with a grayed-out check mark. You can just check it and you can check it again to switch off. The same with the edit ones. In other words, Alias is telling you you've selected entities with the edit points active, and not active, at the same time. It's not a big deal; You just switch them off like this. At this point here I'm gonna go ahead and select all of this data behind.
I'm gonna keep them invisible by pressing I and this now actually is curve data, not Curve on surface data. Let's go back to visible. In this case I'm going to pick the entity at the back here, the Alias word, and just press T for template. If we wanted to we could trim this data out. You could do it very simply by Surface Edit, Trim, Trim Surface. I'm gonna do the 3D trimming because we're gonna use curves here; We don't have a Curve on surface. We only have curves. So we have to check on 3D trimming.
And I'm gonna project Normal, or I could project back in the Y direction. It really doesn't matter. Normal works just fine. Select the surface. And then I'm gonna select the lettering like this and it goes through another calculation. Then I'm gonna select the area that I want to keep. I want to keep that outer portion, this portion here, and this inner portion. Space bar to accept. Let's go ahead, just pick this surface and then press H to hide everything else. Let's do a quick shade on that.
- Manipulating views and entities
- Working with layers
- Creating curves
- Sweeping, extruding, revolving, offsetting, and blending surfaces
- Modifying geometry
- Moving, scaling, flipping, and rotating objects
- Trimming curves and surfaces
- Creating copies of objects
- Aligning, combining, and splitting objects
- Analyzing geometry
- Shading models