This article will talk about some of the principles, requirements and concepts associated with class-A surfacing.
NURBS and Bezier
The difference between NURBS and Beziers (curves and surfaces), that NURBS "support span".Bezier curves have appeared earlier, and after development (support span) became NURBS. So sometimes they say no "patch no span" or "patch span free", and "Bézier surface", or "patch layout Bezier structure" It is believed that NURBS harder to control and therefore came up with a few requirements to the model, complying with these requirements in modeling the model has a class A surfaces. So if the curve 5 degrees and contains 6 CV (7 degree 8 CV, 9 degree 10 CV, 3 degrees 4 CV) can be called a Bezier or NURBS:), but if you let the curve of 3 degrees contains over 4 CV. then call it a Bezier impossible because there is Span.
These pictures can be seen that the same form can be modeled in different ways, different colors are shown Patch, and then how they look together is called Patch Layout (I think this is understandable)
As a general rule for model, create as few patches as possible but enough to reflect the required form of the object.
The main rule for the patch – it
It should be as simple as possible without span-s
tends to a rectangular shape
Avoid multiple curvature directions in single patches.
Primary | Secondary | Tertiary | Rank four surfaces
Primary, Secondary, Tertiary, Rank four surfaces what is it?
Primary - this is the surface created in the first place, bearing surfaces for further modeling. Secondary - a surface connecting the Primary, blend, fillet, etc. Requirements for Primary and Secondary - to achieve Class A necessary that continuity between them was G3 (see below), no span and 7 degree (8 CV). Tertiary - a surface formed with the participation of primary and secondary. Requirements - the minimum curvature continuity G2 (G3 desirable) is allowed up to 7 span (no spans desirable), and the degree can be more than 7. Rank four surfaces - these are the surfaces that are obtained by splitting for example a car body on the parts, hood, doors, trunk, etc. Requirements to them are minimum - allowed G1 continuity, and many spans.
G1 | G2 | G3 | G4
G1 – Tangent continuity. As mentioned above, is used in the most insignificant places, if we are talking about cars, and almost always used in the design of various parts such as engine, gearbox, etc. In general, all the details where the design does not really matter. G1 - where curve (or surface) is blend with another curve on a tangent, but with different radius. To achieve this continuity is sufficient degree of curve 3 with 4 CV Why not use the G1 in the construction of automobiles and other beautiful surfaces can be seen from the video below, because the transition (continuity) from one surface to another is very sharp in spite of the fact that they are tangent to each other.
G2 – Curvature continuity. Most popular continuity in the production of industrial products of any type, vacuum cleaners, hair dryers, cell phones, etc. G2 – where curve (or surface) is blend with another curve on a tangent and the radius of the beginning equal to the radius end of the primary curve (or surface), but is only the start point... this is the difference from G3. To achieve this continuity is sufficient degree of curve 5 with 6 CV G3 – G3 (super curvature :)). G3 – where curve (or surface) is blend with another curve on a tangent and the radius of the beginning equal to the radius end of the primary curve (or surface), and is not just the beginning, but after some point. To achieve this continuity is sufficient degree of curve 7 with 8 CV G4 – mega super G2 :) curve 9 degree with 10 CV
Rhino vs Alias
Rhino vs Alias Blend Tool in Rhino can create surfaces with continuity to the G4. In Alias surface tool Blend got G3 only in the last 2011 version. In the Rhino is no control of the span, which allows you to create a class A.
Curve creation. Create a curve of 3 degrees with 5 CV in Alias Surface in Rhino is almost identical. It creates a curve with one span. But if you delete after two CV, curve in the Alias will disappear because for curve of 3 degrees need at least 4 CV, and Rhino will automatically reduce the degree of curve, and it will continue to appear and work.