# User:LABoyd2/3D objects 150919

## cube

Creates a cube in the first octant. When center is true, the cube is centered on the origin. Argument names are optional if given in the order shown here.

```cube(size = [x,y,z], center = true/false);
cube(size =  x ,     center = true/false);
```
parameters:
size
single value, cube with all sides this length
3 value array [x,y,z], cube with dimensions x, y and z.
center
false (default), 1st (positive) octant, one corner at (0,0,0)
true, cube is centered at (0,0,0)
```default values:  cube();   yields:  cube(size = [1, 1, 1], center = false);
```
examples:
```equivalent scripts for this example
cube(size = 18);
cube(18);
cube([18,18,18]);
.
cube(18,false);
cube([18,18,18],false);
cube([18,18,18],center=false);
cube(size = [18,18,18], center = false);
cube(center = false,size = [18,18,18] );
```
```equivalent scripts for this example
cube([18,28,8],true);
box=[18,28,8];cube(box,true);
```

## sphere

Creates a sphere at the origin of the coordinate system. The argument name is optional.

Parameters

r
Radius. This is the radius of the sphere. The resolution of the sphere will be based on the size of the sphere and the \$fa, \$fs and \$fn variables. For more information on these special variables look at: OpenSCAD_User_Manual/Other_Language_Features
d
Diameter. This is the diameter of the sphere.

(NOTE: d is only available in versions later than 2014.03. Debian is currently known to be behind this)

\$fa
Fragment angle in degrees
\$fs
Fragment size in mm
\$fn
Resolution

Usage Examples

```sphere(r = 1);
sphere(r = 5);
sphere(r = 10);
sphere(d = 2);
sphere(d = 10);
sphere(d = 20);
```
```// this will create a high resolution sphere with a 2mm radius
sphere(2, \$fn=100);
```
```// will also create a 2mm high resolution sphere but this one
// does not have as many small triangles on the poles of the sphere
sphere(2, \$fa=5, \$fs=0.1);
```

## cylinder

Creates a cylinder or cone at the origin of the coordinate system. A single radius (r) makes a cylinder, two different radi (r1, r2) make a cone.

Parameters

h
Decimal. This is the height of the cylinder. Default value is 1.
r
Decimal. The radius of both top and bottom ends of the cylinder. Use this parameter if you want plain cylinder. Default value is 1.
r1
Decimal. This is the radius of the cone on bottom end. Default value is 1.
r2
Decimal. This is the radius of the cone on top end. Default value is 1.
d
Decimal. The diameter of both top and bottom ends of the cylinder. Use this parameter if you want plain cylinder. Default value is 1.
d1
Decimal. This is the diameter of the cone on bottom end. Default value is 1.
d2
Decimal. This is the diameter of the cone on top end. Default value is 1.
center
boolean. If true will center the height of the cone/cylinder around the origin. Default is false, placing the base of the cylinder or r1 radius of cone at the origin.
\$fa
The angle (in degrees) from one fragment to the next. See OpenSCAD_User_Manual/Other_Language_Features.
\$fs
The circumferential length of each fragment. See OpenSCAD_User_Manual/Other_Language_Features.
\$fn
The fixed number of fragments to use. See OpenSCAD_User_Manual/Other_Language_Features.

(NOTE: d,d1,d2 are only available in version later than 2014.03. Debian is currently know to be behind this)

Usage Examples

```cylinder(h = 10, r=20);
cylinder(h = 10, r=20, \$fs=6);
cylinder(h = 10, r1 = 10, r2 = 20, center = false);
cylinder(h = 10, r1 = 20, r2 = 10, center = true);
cylinder(h = 10, d=40);
cylinder(h = 10, d=40, \$fs=6);
cylinder(h = 10, d1 = 20, d2 = 40, center = false);
cylinder(h = 10, d1 = 40, d2 = 20, center = true);
```

Notes on accuracy Circle objects are approximated. The algorithm for doing this matters when you want 3d printed holes to be the right size. Current behaviour is illustrated in a diagram . Discussion regarding optionally changing this behaviour happening in a Pull Request

## polyhedron

Create a polyhedron with a list of points and a list of faces. The point list is all the vertices of the shape, the faces list is how the points relate to the surfaces of the polyhedron.

note: if your version of OpenSCAD is lower than 2014.03 replace "faces" with "triangles" in the below examples

Parameters

points
vector of points or vertices (each a 3 vector).
triangles
(deprecated in version 2014.03, use faces) vector of point triplets (each a 3 number vector). Each number is the 0-indexed point number from the point vector.
faces
(introduced in version 2014.03) vector of point n-tuples with n >= 3. Each number is the 0-indexed point number from the point vector. That is, faces=[[0,1,4]] specifies a triangle made from the first, second, and fifth point listed in points. When referencing more than 3 points in a single tuple, the points must all be on the same plane.
convexity
Integer. The convexity parameter specifies the maximum number of front sides (back sides) a ray intersecting the object might penetrate. This parameter is only needed for correctly displaying the object in OpenCSG preview mode and has no effect on the polyhedron rendering.

Syntax example

``` polyhedron(points = [ [x, y, z], ... ], faces = [ [p1, p2, p3..], ... ], convexity = N);
```

Point ordering for faces When looking at the face from the outside inwards, the points must be clockwise. You can rearrange the order of the points or the order they are referenced in each tuple. The order of faces is immaterial. Note that if your polygons are not all oriented the same way OpenSCAD will either print an error or crash completely, so pay attention to the vertex ordering. Again, remember that the 'pN' components of the faces vector are 0-indexed references to the elements of the points vector.

Example, a square base pyramid:

```polyhedron(
points=[ [10,10,0],[10,-10,0],[-10,-10,0],[-10,10,0], // the four points at base
[0,0,10]  ],                                 // the apex point
faces=[ [0,1,4],[1,2,4],[2,3,4],[3,0,4],              // each triangle side
[1,0,3],[2,1,3] ]                         // two triangles for square base
);
```

## polyhedron - polygon orientation issues

An example of a more complex polyhedron, and showing how to fix polyhedrons with badly oriented polygons.

When you select 'Thrown together' from the view menu and compile the design (not compile and render!) you will see a preview with the mis-oriented polygons highlighted. Unfortunately this highlighting is not possible in the OpenCSG preview mode because it would interfere with the way the OpenCSG preview mode is implemented.)

Below you can see the code and the picture of such a problematic polyhedron, the bad polygons (faces or compositions of faces) are in pink.

```// Bad polyhedron
polyhedron
(points = [
[0, -10, 60], [0, 10, 60], [0, 10, 0], [0, -10, 0], [60, -10, 60], [60, 10, 60],
[10, -10, 50], [10, 10, 50], [10, 10, 30], [10, -10, 30], [30, -10, 50], [30, 10, 50]
],
faces = [
[0,2,3],   [0,1,2],  [0,4,5],  [0,5,1],   [5,4,2],  [2,4,3],
[6,8,9],  [6,7,8],  [6,10,11], [6,11,7], [10,8,11],
[10,9,8], [0,3,9],  [9,0,6], [10,6, 0],  [0,4,10],
[3,9,10], [3,10,4], [1,7,11],  [1,11,5], [1,7,8],
[1,8,2],  [2,8,11], [2,11,5]
]
);
```

A correct polyhedron would be the following:

```polyhedron
(points = [
[0, -10, 60], [0, 10, 60], [0, 10, 0], [0, -10, 0], [60, -10, 60], [60, 10, 60],
[10, -10, 50], [10, 10, 50], [10, 10, 30], [10, -10, 30], [30, -10, 50], [30, 10, 50]
],
faces = [
[0,3,2],  [0,2,1],  [4,0,5],  [5,0,1],  [5,2,4],  [4,2,3],
[6,8,9],  [6,7,8],  [6,10,11],[6,11,7], [10,8,11],
[10,9,8], [3,0,9],  [9,0,6],  [10,6, 0],[0,4,10],
[3,9,10], [3,10,4], [1,7,11], [1,11,5], [1,8,7],
[2,8,1],  [8,2,11], [5,11,2]
]
);
```

Beginner's tip:

If you don't really understand "orientation", try to identify the mis-oriented pink faces and then permute the references to the points vectors until you get it right. E.g. in the above example, the third triangle ([0,4,5]) was wrong and we fixed it as [4,0,5]. In addition, you may select "Show Edges" from the "View Menu", print a screen capture and number both the points and the faces. In our example, the points are annotated in black and the faces in blue. Turn the object around and make a second copy from the back if needed. This way you can keep track.

Clockwise Technique:

Orientation is determined by clockwise indexing. This means that if you're looking at the triangle (in this case [4,0,5]) from the outside you'll see that the path is clockwise around the center of the face. The winding order [4,0,5] is clockwise and therefore good. The winding order [0,4,5] is counter-clockwise and therefore bad. Likewise, any other clockwise order of [4,0,5] works: [5,4,0] & [0,5,4] are good too. If you use the clockwise technique, you'll always have your faces outside (outside of OpenSCAD, other programs do use counter-clockwise as the outside though).

Think of it as a Left Hand Rule:

If you hold the face and the fingers of your hand curls is the same order as the points, then your thumb points outwards.

Succinct description of a 'Polyhedron'

```* Points define all of the points/vertices in the shape.
* Faces is a list of flat polygons that connect up the points/vertices.
```

Each point, in the point list, is defined with a 3-tuple x,y,z position specification. Points in the point list are automatically given an identifier starting at zero for use in the faces list (0,1,2,3,... etc).

Each face, in the faces list, is defined by selecting 3 or more of the points (using the point identifier) out of the point list.

e.g. faces=[ [0,1,2] ] defines a triangle from the first point (points are zero referenced) to the second point and then to the third point.

When looking at any face from the outside, the face must list all points in a clockwise order.