# Fairing with Freeship

Discussion in 'Software' started by Swey, May 6, 2011.

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### philSweetSenior Member

My bad LP. I took some of my own advice when liki posted after me and I (re)read the bloody manual myself. FreeShip aint a NURBs routine, so it could mislead you in some important ways. The Wiki is, however, excellent and very densely crosslinked to other graphics and math topics. I'm referring to the real wiki, not boatdesigns's wiki.

So what you really want to wiki is "subdivision surfaces". I used to write this sort of code back when FORTRAN77 was hot code, so I kinda understand what goes on inside the machine. If the curvature seems to get silly near intersections and the CL, its most likely an artifact of the interpolation scheme being used to push the refined net back closer to the original control points. I tend to only use control curves when I'm adding a bunch of new points with edge split. Once I've got them, I remove the control curve. Also, there are references in the wiki and the manual that suggest that any faces that are not bounded by exactly four points might not smooth nicely around control curves, so try to keep the mesh regular, especially around the perimeter and adjacent to control curves.

Yes LP, that's the reference.

Last edited: May 9, 2011
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### DCockeySenior Member

Depending on the details of the algorithm used, a subdivision surface approaches some version of a NURBS surface as the subdivision surface is divided more and more. Likewise a realization of a NURBS surface using finite facets is generally equivalent to some subdivision surface scheme.

I have a copy of FreeShip Plus which I've looked at but not used yet. I do need to learn how to put surfaces into FreeShip Plus to make use of some the analysis tools it has.
I have been using Rhino which is based on NURBS and gives tremendous control, both local and global, over shapes. Not free however, though relatively inexpensive compared to most other software with similar capabilities.

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### LPFlying Boatman

Phil,
You've touched on some things that I've not seen anybody discuss here. I think it would enhance my usage and many others with a better understanding of the development of surfaces. If you have moment, I have some basic questions regarding the terminology you are using.

A) What do you define as edge split?

B) How does a control curve effect the mesh?

C) What do you call a stub and does it effect fillets and noses?

Thanks.

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