Join Veejay Gahir for an in-depth discussion in this video Offset entities, part of Alias Essential Training.
- Let's take a look at how to offset entities. So the Offset command is an object edit command. So if I open the tab up, or right-click, you're gonna go to Offset. Let's do a Reset to use the default values. In this case these curves are 2D curves, and they're sitting flat in the Top view. So we can use, in this case, an Active view or Geometry average. This will give us the same result. So let's go with Active view. And we have three different types of entities. We have a very simple, single span bezier, and we have a nurb surface, which is multi-span, and then we have a more complex French curve down here, which is 37 spans.
So let's go to the Offset command. We'll pick the first one, and very simply, with the left mouse button, I can move left and right to decide on which direction I want the offset, and at the very top I can have a value dialed in here so I could actually type in an explicit value, of let's say -40 millimeters. Or I can use the slider, but in most cases, you're gonna be using the explicit value or just eyeballing this offset in like that. So let's do a space bar to accept, and that's the result we get.
Again, we can do next and pick the nurbs curve, and again, we can just move very carefully. Now, when you're using this command, you have to be realistic about the distance that we're gonna offset. Don't try to offset too far a distance because then you're gonna start getting errors in the actual quality of the offset, or the accuracy of the offset. So again, we're gonna set something like this, and space bar, and that will set that value. And you'll see in this case here, the edit points are offset normal. So let's open this back up again and go the French curve.
Now this is a lot more complex. Now in this case here, you can see that our temporary graphics are quite distorted. We're getting some very strange results here. Press the space bar, and the result actually is fine. It's just that the temporary graphics gives a little bit of a distorted view of the end result, but the end result itself is fine, but you have to be careful in areas like this. If I light up control points, you can see that we're getting a lot of bunching in areas like that. So again, just be realistic and try to look at what we're asking the curve to do, and what the end result could be, and this is not a desirable condition here.
So let's delete that. Now, if I open this up again, you can see that we're working in the Active view. So, if you are using the Active view, just be careful that if you go into this view here like this and I try to offset this entity, and let's dial in -40 again, like that. Press the space bar, and now if we take a look at that entity, you can see that it's a very strange result. Well, it's because we were in a View mode, and that's a 2D planar entity. So what we can do is we can still offset in a perspective view like this, but what we have to do then is we're gonna change to Geometry average, and the average of this flat geometry is a plane.
So even if we were in this view now, and I did an offset of -40, you can see that we'd get a good result. Okay, we're gonna go back to the Top view, and we're gonna take a look at these two entities here. Now, these are just two simple curves, and this one is one curve. So let's open up Offset again, and we're gonna go back to Active view, and let's take a look at Curve Break Connection. Now with the Curve Break Connection, let's just set this to Off. So if I window over these two entities, and we're gonna pull the offset to about here, and I'm gonna press the space bar to accept, and we end up with a gap here, and that's exactly what we're asking Alias to do for us.
Now with Linear, if I go ahead and pick those two entities, and I want to offset a little bit further, and space bar, what should happen is we should have a linear extension between these two entities here. Now in this particular installation, it's not working correctly, but just to show you what the end result should be, is, I'm just gonna go to Object, Edit, Extend. The result for this should be something similar to this. I'm just gonna eyeball these in, like that. So you should get an extension, and you should get a hard corner like that.
The other option is Circular. So with Circular I can window over these entities, offset like that, space bar, and we should get a circular blend between the two. And again, in this case, it's not working correctly. So what we would see here would be something similar to this. Like that. So again, on this particular installation, it's not working correctly, but that's what those options should do for you with the Extension mode. But in most cases, it's not a big deal.
We can just go ahead and manually extend them and trim them back. Now, in this mode here, we actually have one curve, and if I go back into the Offset command, let's do a Reset on this, and we've got an option for Curve Loop Cutting. Let's just switch that off for a second. I'm gonna select this entity, and if I go back on itself like that, and press the space bar, you can see we have a very strange result, and again, this can cause huge problems downstream if we try to generate a surface with a Sweep or a Loft command from this particular piece of data.
So what we can do, is we can switch on Curve Loop Cutting, and we can specify a radius, and in this case, let's just put in a 100 millimeters. So we'll pick this entity. And now if I offset again like this, press the space bar, you can see what happens. It actually creates a radius, or a smooth transition between the two. Now, even though I specified 100 millimeters, let's do this again and let's specify, let's say, 50 millimeters, and I'm gonna come back a little bit like that, and there.
So you can see we're getting very different results, so it's not that predictable on the internal part of that Curve Loop Cutting command, and the value of 50 millimeters and 100 millimeters is not exactly what we're gonna get here. Nevertheless, this is gonna be a lot better result than having the curve flip back on itself like we can see in this condition here. So if you want to tidy those up, and at least we can create a decent surface from that rather than this condition here. So let's delete those, and let's move on to surfaces now.
So let's shade this up. So what we have here is we have a surface, and onto that surface we've projected this circle. So these are curves on surfaces, and it's simply a simple project in the Y direction. So let's open up Offset again, and let's do a Reset, and I'm just gonna go ahead and pick this surface, and I'm gonna offset it like this, and space bar to accept. Now, if I press h to hide everything else, this is the offset surface. Now you can see with the offset surface, it's actually carried over the curve on surface as well.
Now, if that's what you want to do, you have the option to do that. So let's make everything visible, and let's delete this surface again. Go back to Offset, and we can uncheck Copy Curves on Surfaces. Let's pick this surface again, space bar to accept, and this time you'll see that if I shade this up, we don't have that curve on surface on there. Let's delete that. The other option I want to mention here that's quite important is the Normal mode. So right now we have Off. So when we pick a surface like this and we offset, Alias is trying to do its best to give you the most accurate offset to, let's say, 80 millimeters.
So internally, it's shifting the control points around until it can achieve 80 millimeters. If we select NUV or Normal, what Alias does then, it keeps the normal projection for each control point. So if a control point is located in the corner here, it will offset completely normal to that surface and hold that normal vector. So your control point distribution will be a lot nicer, or it will match the original surface better, but you may not get such an accurate result. I would recommend trying both and just observing the control points and seeing which one looks better.
So finally, let's take a look at these two surfaces here. So these are two independent surfaces. Now you'll notice that this surface here has an associativity to that surface there. So if we go to wire frame, what's the associativity? Well, the associativity is that we have an Align command. So if I move this, you can see that there's an Align command there, and it's basically matching the two together. And, let me show you how I did that very quickly. So, first of all, let's destroy the history here.
We're gonna go to Delete, Construction History, and now these are completely independent. So let's go to Object, Edit, Align, and we're gonna go with just a simple G1 Align. Pick this edge here, doesn't really matter which edge we pick, and then we pick the edge again, and we've put in a tangency constraint. And we'll accept that. Let's press l. So now we have a tangency constraint between the two. So let's go back to Offset. Let's do a Reset. I'm just gonna window over both of those entities, and let's just do an offset again.
The further you offset, the more chance of error. So, just be realistic with the offset. In this case, let's go with 50 millimeters, and I'm gonna do a space bar to accept that. So again, if I pick this entity, you'll notice that both of these entities light up because it's grouped. So let's go to Edit, Ungroup, and now if I pick this entity you'll notice this one doesn't go pink, so there's no associativity between the two entities. But let's go to Evaluate, Continuity, Surface Continuity, and let's check for Tangency.
There's our original surfaces, and that's fine. And these ones here, we've managed to meet tangency continuity with a smaller offset. Now let me show you what happens if we go with a larger offset, we may well break this. So let's go with Offset again, and this time I'm gonna go with a value way up here, space bar to accept, and let's just go straight to Ungroup. Now let's go to Evaluate, Continuity, Surface Continuity, and right now we've lost Positional Continuity. So with a larger distance, we had a greater chance of error, and I'm gonna do Control 5 to open up the Information window, and we can look at the Display, we'll put on the Labels, and you can see that the point that we have lost continuity is with the Positional Continuity, and the error is right at this point here, and the Gap distance is .004, so we've just come out of the core tolerances for Inventor.
So, this is a great way, again, to check where the error is, and in this case, it is quite small, and we could very easily correct that. So let's come out of this. Press l, and we're gonna go to Object, Edit, Align again, and just very simply we're gonna pick this surface. We're gonna lose History on the offset and that's fine. Pick again, and there we are, so we're back to tangency continuity.
- 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