# miniSageCAD

## by mechadense, published

## Thing Info

# Summary

A tool for Constructive Solid Geometry like OpenSCAD but written in Sage http://www.sagemath.org/

There is already quite some functionality in very little code.

You can (via the Jmole 3D viewer in sage) preview & turn the 3d output before saving to *.stl file. With Sage you have a fully blown computer algebra system CAS at hand. Transfinite unbounded objects can be used for construction.

Sages implicit_plot3d is not made for this purpouse so I think this is more useful for experimentation with system design than useful construction work. But I might be wrong.

In this context I like to mention

ImplicitCAD (written by Christopher Olah)

http://www.implicitcad.org/

https://github.com/colah/ImplicitCAD/blob/master/Graphics/Implicit/Primitives.hs

which Is ment to deliver good performance.

I started to code miniSageCAD because while trying sage it became patently obvious to me how easy It'd be to get a minimal useful CSG system.

I wanted to preserve symbolic derivability for all csg expressions (to have symbolic access to the surface normals). I found that only lambdas are symbolically derivable but those lambda expressions can not have line breaks. This makes it necessary to break more complex objects down into subfunctions. A good thing for documentation (names) but bad in that it clutteres the global namespace. Also obstucted by this is the idea to e.g. transport the positions of the edges of a cube up the csg graph accessible in e linearly-transformed way.

** edit: **

new in v0.04:

corrected translate

arbitrary arity union and intersection

prism rod, prism

inshell, onshell, outshell

zfunction

pieslicer

difference2

gyroid (left & right)

# Instructions

Either try it via the public worksheet (note: they are currently disabled 2012-01-04)

http://www.sagenb.org/home/pub/5036/

Or download it and use it within your own sage system.

If you make somthing with it please upload your results.

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How to implement hull or smth for emulating "extrude along the curved path"? In OpenScad I can do this via

union(){

hull(){

translate([0,0,10])rotate(15,[180,0,0])cylinder(h=0.1,r=5);

translate([0,-15,50])rotate(45,[180,0,0])cylinder(h=0.1,r=12);

}

hull(){

translate([0,-15,50])rotate(45,[180,0,0])cylinder(h=0.1,r=12);

translate([0,-30,70])rotate(60,[180,0,0])cylinder(h=0.1,r=20);

}}

Yes convex hulls are painfully lacking.

The reason is that convex hulls are rather nontrivial:

http://en.wikipedia.org/wiki/Convex_hull_algorithmshttp://en.wikipedia.org/wiki/C...

I think todays practically used algorithms are all vertex based.

You'd have to find a general way to generate an implicit function Surf(c):={x,y,z|f_hull(x,y,z)=c} such that forall c: Surf(c)=boundary(hull(Surf1(c),surf2(c),..)) without relying on vertex based algorithms. I guess that there isn't a noniterative direct way to do that. A hull of compositioned objects (planes & tubes) like your example is even harder. Concrete example: For easier reasoning imagine the convex hull of two circles in a two dimensional room. The implicit function for a circle is a cone. You'd have to generate a "roof" from this two cones only with elementary functions (provable impossible?).

Special cases could be implemented though. And I think this (with auto case choice) is a good way to go. Sadly two arbitrary orientated circles like in your specific case will not work this way. But e.g. a truncated cone as convex hull for two spheres will. In Haskell types could carry the necessary information or monads, but in sage I see hurdles/limits.

Another (less powerful) approach for things similar to this would be to to define an implicit function by the minimal distance to an user choosen parametrically defined spacecurve x(t),y(t),z(t).

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