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Kayak and Canoe Design Bulletin Board
Re: List ettiquette
Posted By: Nick Schade In Response To: Re: New Wave Systems hull design software (John Winters)
Date: Friday, 21 May 1999, at 9:55 a.m.
List ettiquette is still a little loose. At this time, just try not to antagonize "the competition". Since there is not much competition for your book, it would be hard to antagonize anyone by mentioning it here.
Feel free to discuss general technical terminology on this board. If the terminology is specific only to one software package, it might not be that interesting, but chances are anything in Nautilus is relevant to other software.
For example: I don't like the "Surface Points" editing method of the surfaces used in Nautilus. Contrary to what Mr Hollister says, I find it makes it more difficult to fair out the hull than the "Vertex Points". The Surface method tends to introduce more "inflection" points into the surface. Inflection points are where a curve changes from concave in one direction to convex in that direction.
To see this, try to make a straight line with 6 control points (2 end points and 4 intermediate controls). Try moving the second point. You will get a series of diminising waves proceeding through the curve when using the surface point-interpolated editing method. A slight change in any one point makes the whole line wiggly and non-fair. It is a little better with the Surface Point - Local method, but in this case the control point may not be on the part of the line most effected by the control point, ie you get a more motion away from the point than at the point.
One of the beauties of B-Spline curves like NURBS is that the character of the curve matches the character of the control vertex. If you align the control vertex in a fair curve, the spline will be fair. The number of inflection points on the spline will always equal the number in the vertex mesh. Also control vertex effects the curve closest to the vertex the most.
A fair hull requires a fair vertex mesh. The surface controls and the interpolation methods required to make them work can create a horrendous mess of a vertex mesh and while resulting hull may look fair on screen, if the vertex mesh is ugly, chances are very good that the hull is not fair.
In my opinion working directly with the vertex mesh gives far more control over the shape than working with the surface points. While while control points on the surface are easier to understand, the vertex points of a fair surface are rarely far from the surface so they are not that hard to understand, and in the long run more control is easier than less.
As an example, lets say you want the deck of your boat to flow smoothly into the hull. If you make the shared surface edge vertex and the next vertices in on each surface all lie on one straight line, the edges of the two surfaces will match without a crease, guarranteed. You do not have this ability with control points which lie on the surface. Trying to make that smooth joint would be very difficult.
Luckily Nautilus gives you both control methods which may give slightly more overall control than editing the vertex mesh alone.
> I have a glossary of common terms at
> http://home.ican.net/~735769/glossary.htm You might find it worthwhile
> reading some of my pages on canoe and kayak design to get a rough idea of
> primary concerns. My book (are we allowed to plug our books here? I will
> take a chance and apologise now if I have breeched list ettiquette), The
> Shape of The Canoe contains more detailed information on design.> If you have specific questions about terminology on Nautilus I will be
> happy to answer them off list since it will bore most readers on the list.> Cheers, John Winters
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Kayak and Canoe Design Bulletin Board is maintained by Nick Schade - Guillemot Kayaks with WebBBS 5.12.
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