From the course: CATIA V5: Class A Surfacing

Primary, secondary, and tertiary geometry - CATIA Tutorial

From the course: CATIA V5: Class A Surfacing

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Primary, secondary, and tertiary geometry

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- [Instructor] When you're designing your Class A surfaces, there are three things you have to consider: your primaries, your secondaries, and your tertiaries. Your primary slabs are your biggest, most general shapes. They basically capture most of the intent. Your secondaries, these blue surfaces here are typically your blends between primary surfaces. These primary surfaces have a nice general flow capturing the largest slabs, over built geometry. So easier to overbuild and come back and trim things up as necessary. So to connect these primary slabs, we put these secondary surfaces in, and oftentimes, where secondaries and other primaries come together to form these little, almost ball corners, they're called tertiary surfaces. These are typically the most mathematically complex because they are built off of blend surfaces, which they themselves are relatively complex. For every order of continuity that you require out of a surface, you have additional math that needs to be imparted on that surface, and coming off of your primary surfaces which, even though they're the biggest shapes, they should be the simplest mathematical representations of shape in your part. We want to try to minimize the amount of math in these, and the reason is because every downstream function is going to increase the complexity of said surfaces, so the next surface built off of it's going to be a little more complex, and so on and so forth until we get into our tertiary surfaces. As you can see here, generally speaking our tertiary surfaces, these little ball corners, are the last things that we build. These are the things that are just taking, in this case, a tight little corner, wrapping it around these big, gentle blends, and just finishing off those surfaces. So when you're laying out these patches, when you're laying out your design, you want to try to encapsulate as much of that design with your primaries, and then think about where your tangencies are going to go to bridge across those primaries with your initial secondaries, and then to close everything off with that final tertiary surface.

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