OpenSCAD User Manual/Using the 2D Subsystem
2D Primitives Edit
All 2D primitives can be transformed with 3D transformations. They are usually used as part of a 3D extrusion. Although they are infinitely thin, they are rendered with a 1 thickness.
Note: The try to substract with difference()
from 3D object will lead to unexpected results in final rendering.
squareEdit
Creates a square or rectangle in the first quadrant. When center
is true the square is centered on the origin. Argument names are optional if given in the order shown here.
square(size = [x, y], center = true/false); square(size = x , center = true/false);
 parameters:
 size
 single value, square with both sides this length
 2 value array [x,y], rectangle with dimensions x and y
 center
 false (default), 1st (positive) quadrant, one corner at (0,0)
 true, square is centered at (0,0)
 size
default values: square(); yields: square(size = [1, 1], center = false);
 examples:
equivalent scripts for this example square(size = 10); square(10); square([10,10]); . square(10,false); square([10,10],false); square([10,10],center=false); square(size = [10, 10], center = false); square(center = false,size = [10, 10] );
equivalent scripts for this example square([20,10],true); a=[20,10];square(a,true);
circleEdit
Creates a circle at the origin. All parameters, except r, must be named.
circle(r=radius  d=diameter);
 Parameters
 r : circle radius. r name is the only one optional with circle.
 circle resolution is based on size, using $fa or $fs.
 r : circle radius. r name is the only one optional with circle.
 For a small, high resolution circle you can make a large circle, then scale it down, or you could set $fn or other special variables. Note: These examples exceed the resolution of a 3d printer as well as of the display screen.
scale([1/100, 1/100, 1/100]) circle(200); // create a high resolution circle with a radius of 2. circle(2, $fn=50); // Another way.
 d : circle diameter (only available in versions later than 2014.03).
 $fa : minimum angle (in degrees) of each fragment.
 $fs : minimum circumferential length of each fragment.
 $fn : fixed number of fragments in 360 degrees. Values of 3 or more override $fa and $fs.
 If they are used, $fa, $fs and $fn must be named parameters. click here for more details,.
defaults: circle(); yields: circle($fn = 0, $fa = 12, $fs = 2, r = 1);
Equivalent scripts for this example
circle(10); circle(r=10); circle(d=20); circle(d=2+9*2);
EllipsesEdit
An ellipse can be created from a circle by using either scale()
or resize()
to make the x and y dimensions unequal.
See OpenSCAD User Manual/Transformations
equivalent scripts for this example resize([30,10])circle(d=20); scale([1.5,.5])circle(d=20);
Regular PolygonsEdit
A regular polygon of 3 or more sides can be created by using circle()
with $fn set to the number of sides. The following two pieces of code are equivalent.
circle(r=1, $fn=4);
module regular_polygon(order = 4, r=1){ angles=[ for (i = [0:order1]) i*(360/order) ]; coords=[ for (th=angles) [r*cos(th), r*sin(th)] ]; polygon(coords); } regular_polygon();
These result in the following shapes, where the polygon is inscribed within the circle with all sides (and angles) equal. One corner points to the positive x direction. For irregular shapes see the polygon primitive below.
script for these examples translate([42, 0]){circle(20,$fn=3);%circle(20,$fn=90);} translate([ 0, 0]) circle(20,$fn=4); translate([ 42, 0]) circle(20,$fn=5); translate([42,42]) circle(20,$fn=6); translate([ 0,42]) circle(20,$fn=8); translate([ 42,42]) circle(20,$fn=12); color("black"){ translate([42, 0,1])text("3",7,,center); translate([ 0, 0,1])text("4",7,,center); translate([ 42, 0,1])text("5",7,,center); translate([42,42,1])text("6",7,,center); translate([ 0,42,1])text("8",7,,center); translate([ 42,42,1])text("12",7,,center); }
polygonEdit
The function polygon() creates a multiple sided shape from a list of x,y coordinates. A polygon is the most powerful 2D object. It can create anything that circle and squares can, as well as much more. This includes irregular shapes with both concave and convex edges. In addition it can place holes within that shape.
polygon(points = [ [x, y], ... ], paths = [ [p1, p2, p3..], ...], convexity = N);
 Parameters
 points
 The list of x,y points of the polygon. : A vector of 2 element vectors.
 Note: points are indexed from 0 to n1.
 paths
 default
 If no path is specified, all points are used in the order listed.
 single vector
 The order to traverse the points. Uses indices from 0 to n1. May be in a different order and use all or part, of the points listed.
 multiple vectors
 Creates primary and secondary shapes. Secondary shapes are subtracted from the primary shape (like
difference()
). Secondary shapes may be wholly or partially within the primary shape.
 Creates primary and secondary shapes. Secondary shapes are subtracted from the primary shape (like
 default
 A closed shape is created by returning from the last point specified to the first.
 convexity
 Integer number of "inward" curves, ie. expected path crossings of an arbitrary line through the polygon. See below.
defaults: polygon(); yields: polygon(points = undef, paths = undef, convexity = 1);
Without holesEdit
equivalent scripts for this example polygon(points=[[0,0],[100,0],[130,50],[30,50]]); polygon([[0,0],[100,0],[130,50],[30,50]], paths=[[0,1,2,3]]); polygon([[0,0],[100,0],[130,50],[30,50]],[[3,2,1,0]]); polygon([[0,0],[100,0],[130,50],[30,50]],[[1,0,3,2]]); a=[[0,0],[100,0],[130,50],[30,50]]; b=[[3,0,1,2]]; polygon(a); polygon(a,b); polygon(a,[[2,3,0,1,2]]);
One holeEdit
equivalent scripts for this example polygon(points=[[0,0],[100,0],[0,100],[10,10],[80,10],[10,80]], paths=[[0,1,2],[3,4,5]],convexity=10); triangle_points =[[0,0],[100,0],[0,100],[10,10],[80,10],[10,80]]; triangle_paths =[[0,1,2],[3,4,5]]; polygon(triangle_points,triangle_paths,10);
The 1st path vector, [0,1,2], selects the points, [0,0],[100,0],[0,100], for the primary shape.
The 2nd path vector, [3,4,5], selects the points, [10,10],[80,10],[10,80], for the secondary shape.
The secondary shape is subtracted from the primary ( think difference()
).
Since the secondary is wholly within the primary, it leaves a shape with a hole.
Multi holeEdit
[Note: Requires version 2015.03] (for use of concat()
)
//example polygon with multiple holes a0 = [[0,0],[100,0],[130,50],[30,50]]; // main b0 = [1,0,3,2]; a1 = [[20,20],[40,20],[30,30]]; // hole 1 b1 = [4,5,6]; a2 = [[50,20],[60,20],[40,30]]; // hole 2 b2 = [7,8,9]; a3 = [[65,10],[80,10],[80,40],[65,40]]; // hole 3 b3 = [10,11,12,13]; a4 = [[98,10],[115,40],[85,40],[85,10]]; // hole 4 b4 = [14,15,16,17]; a = concat (a0,a1,a2,a3,a4); b = [b0,b1,b2,b3,b4]; polygon(a,b); //alternate polygon(a,[b0,b1,b2,b3,b4]);
Extruding a 3D shape from a polygonEdit
translate([0,20,10]) { rotate([90,180,90]) { linear_extrude(50) { polygon( points = [ //x,y /* O . */ [2.8,0], /* O__X . */ [7.8,0], /* O \ X__X . */ [15.3633,10.30], /* X_______._____O \ X__X . */ [15.3633,10.30], /* X_______._______X \ / X__X . O */ [7.8,0], /* X_______._______X \ / X__X . O__X */ [2.8,0], /* X__________.__________X \ / \ O / \ / / \ / / X__X . X__X */ [5.48858,5.3], /* X__________.__________X \ / \ O__________X / \ / / \ / / X__X . X__X */ [5.48858,5.3], ] ); } } }
convexityEdit
The convexity parameter specifies the maximum number of front sides (back sides) a ray intersecting the object might penetrate. This parameter is needed only for correct display of the object in OpenCSG preview mode and has no effect on the polyhedron rendering.
This image shows a 2D shape with a convexity of 2, as the ray indicated in red crosses the 2D shapes outside⇒inside (or inside⇒outside) a maximum of 2 times. The convexity of a 3D shape would be determined in a similar way. Setting it to 10 should work fine for most cases.
import_dxfEdit
[Deprecated: import_dxf() will be removed in future releases. Use import() instead.]
Read a DXF file and create a 2D shape.
Example
linear_extrude(height = 5, center = true, convexity = 10) import_dxf(file = "example009.dxf", layer = "plate");
Text Edit
The text
module creates text as a 2D geometric object,
using fonts installed on the local system or provided as separate font file.
[Note: Requires version 2015.03]
Parameters
 text
 String. The text to generate.
 size
 Decimal. The generated text has an ascent (height above the baseline) of approximately the given value. Default is 10. Different fonts can vary somewhat and may not fill the size specified exactly, typically they render slightly smaller. On a metric system a size of 25.4 (1" imperial) will correspond to 100pt ⇒ a 12pt font size would be 12×0.254 for metric conversion or 0.12 in imperial.
 font
 String. The name of the font that should be used. This is not the name of the font file, but the logical font name (internally handled by the fontconfig library). This can also include a style parameter, see below. A list of installed fonts & styles can be obtained using the font list dialog (Help > Font List).
 halign
 String. The horizontal alignment for the text. Possible values are "left", "center" and "right". Default is "left".
 valign
 String. The vertical alignment for the text. Possible values are "top", "center", "baseline" and "bottom". Default is "baseline".
 spacing
 Decimal. Factor to increase/decrease the character spacing. The default value of 1 results in the normal spacing for the font, giving a value greater than 1 causes the letters to be spaced further apart.
 direction
 String. Direction of the text flow. Possible values are "ltr" (lefttoright), "rtl" (righttoleft), "ttb" (toptobottom) and "btt" (bottomtotop). Default is "ltr".
 language
 String. The language of the text. Default is "en".
 script
 String. The script of the text. Default is "latin".
 $fn
 used for subdividing the curved path segments provided by freetype
Example
text("OpenSCAD");
 Notes
To allow specification of particular Unicode characters, you can specify them in a string with the following escape codes;
 \x03  hex charvalue (only hex values from 01 to 7f are supported)
 \u0123  Unicode char with 4 hexadecimal digits (note: lowercase \u)
 \U012345  Unicode char with 6 hexadecimal digits (note: uppercase \U)
The null character (NUL) is mapped to the space character (SP).
assert(version() == [2019, 5, 0]); assert(ord(" ") == 32); assert(ord("\x00") == 32); assert(ord("\u0000") == 32); assert(ord("\U000000") == 32);
Example
t="\u20AC10 \u263A"; // 10 euro and a smilie
Using Fonts & StylesEdit
Fonts are specified by their logical font name; in addition a style parameter can be added to select a specific font style like "bold" or "italic", such as:
font="Liberation Sans:style=Bold Italic"
The font list dialog (available under Help > Font List) shows the font name and the font style for each available font. For reference, the dialog also displays the location of the font file. You can drag a font in the font list, into the editor window to use in the text() statement.
OpenSCAD includes the fonts Liberation Mono, Liberation Sans, and Liberation Serif. Hence, as fonts in general differ by platform type, use of these included fonts is likely to be portable across platforms.
For common/casual text usage, the specification of one of these fonts is recommended for this reason. Liberation Sans is the default font to encourage this.
In addition to the installed fonts ( for windows only fonts installed as admin for all users ), it's possible to add project specific font files. Supported font file formats are TrueType Fonts (*.ttf) and OpenType Fonts (*.otf). The files need to be registered with use<>.
use <ttf/paratypeserif/PTF55F.ttf>
After the registration, the font is listed in the font list dialog, so in case logical name of a font is unknown, it can be looked up as it was registered.
OpenSCAD uses fontconfig to find and manage fonts, so it's possible to list the system configured fonts on command line using the fontconfig tools in a format similar to the GUI dialog.
$ fclist f "%60{{%{family[0]}%{:style[0]=}}}%{file}\n"  sort
...
Liberation Mono:style=Bold Italic /usr/share/fonts/truetype/liberation2/LiberationMonoBoldItalic.ttf
Liberation Mono:style=Bold /usr/share/fonts/truetype/liberation2/LiberationMonoBold.ttf
Liberation Mono:style=Italic /usr/share/fonts/truetype/liberation2/LiberationMonoItalic.ttf
Liberation Mono:style=Regular /usr/share/fonts/truetype/liberation2/LiberationMonoRegular.ttf
...
Under Windows, fonts are stored in the Windows Registry. To get a file with the font file names, use the command:
reg query "HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Fonts" /s > List_Fonts_Windows.txt
Example
square(10); translate([15, 15]) { text("OpenSCAD", font = "Liberation Sans"); } translate([15, 0]) { text("OpenSCAD", font = "Liberation Sans:style=Bold Italic"); }
AlignmentEdit
Vertical alignmentEdit
 top
 The text is aligned with the top of the bounding box at the given Y coordinate.
 center
 The text is aligned with the center of the bounding box at the given Y coordinate.
 baseline
 The text is aligned with the font baseline at the given Y coordinate. This is the default.
 bottom
 The text is aligned with the bottom of the bounding box at the given Y coordinate.
text = "Align"; font = "Liberation Sans"; valign = [ [ 0, "top"], [ 40, "center"], [ 75, "baseline"], [110, "bottom"] ]; for (a = valign) { translate([10, 120  a[0], 0]) { color("red") cube([135, 1, 0.1]); color("blue") cube([1, 20, 0.1]); linear_extrude(height = 0.5) { text(text = str(text,"_",a[1]), font = font, size = 20, valign = a[1]); } } }
Multi line text is not supported with `text()` but translating each line size × .72 will result in a leading (line spaceing) of 1 em (em= fonts body height or points). 20% (× 1.2) may be added.
Horizontal alignmentEdit
 left
 The text is aligned with the left side of the bounding box at the given X coordinate. This is the default.
 center
 The text is aligned with the center of the bounding box at the given X coordinate.
 right
 The text is aligned with the right of the bounding box at the given X coordinate.
text = "Align"; font = "Liberation Sans"; halign = [ [10, "left"], [50, "center"], [90, "right"] ]; for (a = halign) { translate([140, a[0], 0]) { color("red") cube([115, 2,0.1]); color("blue") cube([2, 20,0.1]); linear_extrude(height = 0.5) { text(text = str(text,"_",a[1]), font = font, size = 20, halign = a[1]); } } }
3D textEdit
Text can be changed from a 2 dimensional object into a 3D object by using the linear_extrude function.
//3d Text Example linear_extrude(4) text("Text");
3D to 2D Projection Edit
Using the projection()
function, you can create 2d drawings from 3d models, and export them to the dxf format. It works by projecting a 3D model to the (x,y) plane, with z at 0. If cut=true
, only points with z=0 are considered (effectively cutting the object), with cut=false
(the default), points above and below the plane are considered as well (creating a proper projection).
Example: Consider example002.scad, that comes with OpenSCAD.
Then you can do a 'cut' projection, which gives you the 'slice' of the xy plane with z=0.
projection(cut = true) example002();
You can also do an 'ordinary' projection, which gives a sort of 'shadow' of the object onto the xy plane.
projection(cut = false) example002();
Another Example
You can also use projection to get a 'side view' of an object. Let's take example002, and move it up, out of the XY plane, and rotate it:
translate([0,0,25]) rotate([90,0,0]) example002();
Now we can get a side view with projection()
projection() translate([0,0,25]) rotate([90,0,0]) example002();
Links:
 example021.scad from Clifford Wolf's site.
 More complicated example from Giles Bathgate's blog
2D to 3D Extrusion Edit
Extrusion is the process of creating an object with a fixed crosssectional profile. OpenSCAD provides two commands to create 3D solids from a 2D shape: linear_extrude() and rotate_extrude(). Linear extrusion is similar to pushing Playdoh through a press with a die of a specific shape.
Rotational extrusion is similar to the process of turning or "throwing" a bowl on the Potter's wheel.
Both extrusion methods work on a (possibly disjointed) 2D shape which exists on the XY plane. While transformations that operates on both 2D shapes and 3D solids can move a shape off the XY plane, when the extrusion is performed the end result is not very intuitive. What actually happens is that any information in the third coordinate (the Z coordinate) is ignored for any 2D shape, this process amounts to an implicit projection() performed on any 2D shape before the extrusion is executed. It is recommended to perform extrusion on shapes that remains strictly on the XY plane.
linear_extrudeEdit
Linear Extrusion is an operation that takes a 2D object as input and generates a 3D object as a result.
In OpenSCAD Extrusion is always performed on the projection (shadow) of the 2d object xy plane and along the Z axis; so if you rotate or apply other transformations to the 2d object before extrusion, its shadow shape is what is extruded.
Although the extrusion is linear along the Z axis, a twist parameter is available that causes the object to be rotated around the Z axis as it is extruding upward. This can be used to rotate the object at its center, as if it is a spiral pillar, or produce a helical extrusion around the Z axis, like a pig's tail.
A scale parameter is also included so that the object can be expanded or contracted over the extent of the extrusion, allowing extrusions to be flared inward or outward.
UsageEdit
linear_extrude(height = 5, center = true, convexity = 10, twist = fanrot, slices = 20, scale = 1.0, $fn = 16) {...}
You must use parameter names due to a backward compatibility issue.
height
must be positive.
$fn
is optional and specifies the resolution of the linear_extrude (higher number brings more "smoothness", but more computation time is needed).
If the extrusion fails for a nontrivial 2D shape, try setting the convexity parameter (the default is not 10, but 10 is a "good" value to try). See explanation further down.
TwistEdit
Twist is the number of degrees of through which the shape is extruded. Setting the parameter twist = 360 extrudes through one revolution. The twist direction follows the left hand rule.
0° of Twist
linear_extrude(height = 10, center = true, convexity = 10, twist = 0) translate([2, 0, 0]) circle(r = 1);
100° of Twist
linear_extrude(height = 10, center = true, convexity = 10, twist = 100) translate([2, 0, 0]) circle(r = 1);
100° of Twist
linear_extrude(height = 10, center = true, convexity = 10, twist = 100) translate([2, 0, 0]) circle(r = 1);
500° of Twist
linear_extrude(height = 10, center = true, convexity = 10, twist = 500) translate([2, 0, 0]) circle(r = 1);
CenterEdit
It is similar to the parameter center of cylinders. If center
is false the linear extrusion Z range is from 0 to height; if it is true, the range is from height/2 to height/2.
center = true
linear_extrude(height = 10, center = true, convexity = 10, twist = 500) translate([2, 0, 0]) circle(r = 1);
center = false
linear_extrude(height = 10, center = false, convexity = 10, twist = 500) translate([2, 0, 0]) circle(r = 1);
Mesh RefinementEdit
The slices parameter defines the number of intermediate points along the Z axis of the extrusion. Its default increases with the value of twist. Explicitly setting slices may improve the output refinement. Additional the segments parameter adds vertices (points) to the extruded polygon resulting in smoother twisted geometries. Segments need to be a multiple of the polygon's fragments to have an effect (6 or 9.. for a circle($fn=3), 8,12.. for a square() ).
linear_extrude(height = 10, center = false, convexity = 10, twist = 360, slices = 100) translate([2, 0, 0]) circle(r = 1);
The special variables $fn, $fs and $fa can also be used to improve the output. If slices is not defined, its value is taken from the defined $fn value.
linear_extrude(height = 10, center = false, convexity = 10, twist = 360, $fn = 100) translate([2, 0, 0]) circle(r = 1);
ScaleEdit
Scales the 2D shape by this value over the height of the extrusion. Scale can be a scalar or a vector:
linear_extrude(height = 10, center = true, convexity = 10, scale=3) translate([2, 0, 0]) circle(r = 1);
linear_extrude(height = 10, center = true, convexity = 10, scale=[1,5], $fn=100) translate([2, 0, 0]) circle(r = 1);
Note that if scale is a vector, the resulting side walls may be nonplanar. Use twist=0
and the slices
parameter to avoid asymmetry.
linear_extrude(height=10, scale=[1,0.1], slices=20, twist=0) polygon(points=[[0,0],[20,10],[20,10]]);
rotate_extrudeEdit
Rotational extrusion spins a 2D shape around the Zaxis to form a solid which has rotational symmetry. One way to think of this operation is to imagine a Potter's wheel placed on the XY plane with its axis of rotation pointing up towards +Z. Then place the tobemade object on this virtual Potter's wheel (possibly extending down below the XY plane towards Z). The tobemade object is the crosssection of the object on the XY plane (keeping only the right half, X >= 0). That is the 2D shape that will be fed to rotate_extrude() as the child in order to generate this solid. Note that the object started on the XY plane but is tilted up (rotated +90 degrees about the Xaxis) to extrude.
Since a 2D shape is rendered by OpenSCAD on the XY plane, an alternative way to think of this operation is as follows: spins a 2D shape around the Yaxis to form a solid. The resultant solid is placed so that its axis of rotation lies along the Zaxis.
Just like the linear_extrude, the extrusion is always performed on the projection of the 2D polygon to the XY plane. Transformations like rotate, translate, etc. applied to the 2D polygon before extrusion modify the projection of the 2D polygon to the XY plane and therefore also modify the appearance of the final 3D object.
 A translation in Z of the 2D polygon has no effect on the result (as also the projection is not affected).
 A translation in X increases the diameter of the final object.
 A translation in Y results in a shift of the final object in Z direction.
 A rotation about the X or Y axis distorts the cross section of the final object, as also the projection to the XY plane is distorted.
Don't get confused, as OpenSCAD renders 2D polygons with a certain height in the Z direction, so the 2D object (with its height) appears to have a bigger projection to the XY plane. But for the projection to the XY plane and also for the later extrusion only the base polygon without height is used.
It can not be used to produce a helix or screw threads. (These things can be done with linear_extrude() using the twist parameter.)
The 2D shape must lie completely on either the right (recommended) or the left side of the Yaxis. More precisely speaking, every vertex of the shape must have either x >= 0 or x <= 0. If the shape spans the X axis a warning appears in the console windows and the rotate_extrude() is ignored. If the 2D shape touches the Y axis, i.e. at x=0, it must be a line that touches, not a point, as a point results in a zero thickness 3D object, which is invalid and results in a CGAL error. For OpenSCAD versions prior to 2016.xxxx, if the shape is in the negative axis the resulting faces are oriented insideout, which may cause undesired effects.
UsageEdit
rotate_extrude(angle = 360, convexity = 2) {...}
You must use parameter names due to a backward compatibility issue.
 convexity : If the extrusion fails for a nontrival 2D shape, try setting the convexity parameter (the default is not 10, but 10 is a "good" value to try). See explanation further down.
 angle [Note: Requires version 2019.05] : Defaults to 360. Specifies the number of degrees to sweep, starting at the positive X axis. The direction of the sweep follows the Right Hand Rule, hence a negative angle sweeps clockwise.
 $fa : minimum angle (in degrees) of each fragment.
 $fs : minimum circumferential length of each fragment.
 $fn : fixed number of fragments in 360 degrees. Values of 3 or more override $fa and $fs
 $fa, $fs and $fn must be named parameters. click here for more details,.
ExamplesEdit
A simple torus can be constructed using a rotational extrude.
rotate_extrude(convexity = 10) translate([2, 0, 0]) circle(r = 1);
Mesh RefinementEdit
Increasing the number of fragments composing the 2D shape improves the quality of the mesh, but takes longer to render.
rotate_extrude(convexity = 10) translate([2, 0, 0]) circle(r = 1, $fn = 100);
The number of fragments used by the extrusion can also be increased.
rotate_extrude(convexity = 10, $fn = 100) translate([2, 0, 0]) circle(r = 1, $fn = 100);
Using the parameter angle (with OpenSCAD versions 2016.xx), a hook can be modeled .
eps = 0.01; translate([eps, 60, 0]) rotate_extrude(angle=270, convexity=10) translate([40, 0]) circle(10); rotate_extrude(angle=90, convexity=10) translate([20, 0]) circle(10); translate([20, eps, 0]) rotate([90, 0, 0]) cylinder(r=10, h=80+eps);
Extruding a PolygonEdit
Extrusion can also be performed on polygons with points chosen by the user.
Here is a simple polygon and its 200 step rotational extrusion. (Note it has been rotated 90 degrees to show how the rotation appears; the rotate_extrude()
needs it flat).
rotate([90,0,0]) polygon( points=[[0,0],[2,1],[1,2],[1,3],[3,4],[0,5]] );
rotate_extrude($fn=200) polygon( points=[[0,0],[2,1],[1,2],[1,3],[3,4],[0,5]] );
For more information on polygons, please see: 2D Primitives: Polygon.
Description of extrude parametersEdit
Extrude parameters for all extrusion modesEdit
convexity  Integer. The convexity parameter specifies the maximum number of front sides (or back sides) a ray intersecting the object might penetrate. This parameter is only needed for correctly displaying the object in OpenCSG preview mode when using the standard Goldfeather algorithm and has no effect on the polyhedron rendering (the mesh generation).

This image shows a 2D shape with a convexity of 2, as the ray indicated in red crosses the 2D shape a maximum of 4 times (2 front sides and 2 back sides). The convexity of a 3D shape would be determined in a similar way. Setting it to 10 should work fine for most cases. Just setting high numbers in general may result in slower preview rendering.
Extrude parameters for linear extrusion onlyEdit
height  The extrusion height 
center  If true, the solid is centered after extrusion 
twist  The extrusion twist in degrees 
scale  Scales the 2D shape by this value over the height of the extrusion. 
slices  Similar to special variable $fn without being passed down to the child 2D shape. 
segments  Similar to slices but adding points on the polygon's segments without changing the polygon's shape. 
DXF Extrusion Edit
With the import() and extrusion modules it is possible to convert 2D objects read from DXF files to 3D objects. See also 2D to 3D Extrusion.
Linear ExtrudeEdit
Example of linear extrusion of a 2D object imported from a DXF file.
linear_extrude(height = fanwidth, center = true, convexity = 10) import (file = "example009.dxf", layer = "fan_top");
Rotate ExtrudeEdit
Example of rotational extrusion of a 2D object imported from a DXF file.
rotate_extrude(convexity = 10) import (file = "example009.dxf", layer = "fan_side", origin = fan_side_center);
Getting Inkscape to workEdit
Inkscape is an open source drawing program. Tutorials for transferring 2d DXF drawings from Inkscape to OpenSCAD are available here:
 http://repraprip.blogspot.com/2011/05/inkscapetoopenscaddxftutorial.html (Very simple, needs path segments to be straight lines)
 http://tonybuser.com/?tag=inkscape (More complicated, involves conversion to Postscript)
 http://bobcookdev.com/inkscape/inkscapedxf.html (Better DXF Export, native support for bezier curves)
 http://www.bigbluesaw.com/saw/bigbluesawblog/generalupdates/bigbluesawsdxfexportforinkscape.html (even better support, works as of 10/29/2014, see link below registration window. Note: As of 6/17/15 only works with version 0.48.5 or earlier of inkscape, due to a breaking change made in 0.91.)
 http://www.instructables.com/id/Convertany2Dimagetoa3DobjectusingOpenSCAD/ (Convert any 2D image to a 3D object using OpenSCAD)
 http://carrefournumerique.citesciences.fr/fablab/wiki/doku.php?id=projets:de_inkscape_a_openscad (French, directly exports OpenSCAD file)