Apertures in Gerbonara

Gerbonara maps all standard Gerber apertures to subclasses of the Aperture class. These subclasses: CircleAperture, RectangleAperture, ObroundAperture and PolygonAperture. Aperture macro instantiations get mapped to ApertureMacroInstance (also an Aperture subclass).

All Aperture subclasses have these common attributes:

hole_dia: float with diameter of hole. 0 for no hole.
hole_rect_h: float or None. If not None, specifies a rectangular hole of size hole_dia * hole_rect_h instead of a round hole.
unit: LengthUnit for all of this aperture's fields
attrs: GerberX2 attributes of this aperture. Note that this will only contain aperture attributes, not file attributes. File attributes are stored in the attrs of GerberFile.
original_number: int of aperture index this aperture had when it was read from the Gerber file. This field is purely informational since apertures are de-duplicated and re-numbered when writing a Gerber file. For D10, this field would be 10. If you programmatically create a new aperture, you do not have to set this.
rotation: Aperture rotation in radians counter-clockwise. This field is not part of the Gerber standard. Standard rectangle and obround apertures do not support rotation. Gerbonara converts rotated apertures into aperture macros during Gerber export as necessary.

CircleAperture

This is the only one valid for use in Line or Arc.

Attributes:

Common attributes:: hole_dia, hole_rect_h, unit, attrs, and original_number. rotation is present but has no effect in CircleAperture.
diameter: float with diameter of aperture in the unit from the aperture's unit field.

RectangleAperture

Common attributes:: hole_dia, hole_rect_h, unit, attrs, original_number, and rotation
w, h: floats with width or height of rectangle in units from the aperture's unit field.

ObroundAperture

Aperture whose shape is the convex hull of two circles of equal radii.

Common attributes:: hole_dia, hole_rect_h, unit, attrs, original_number, and rotation
w, h: floats with width and height of bounding box of obround. The smaller one of these will be the diameter of the obround's ends. If w is larger, the result will be a landscape obround. If h is larger, it will be a portrait obround.

PolygonAperture

Aperture whose shape is a regular n-sided polygon (e.g. pentagon, hexagon etc.).

Common attributes:: hole_dia, unit, attrs, original_number, and rotation. hole_rect_h is not supported in PolygonAperture since the Gerber spec does not list it.
diameter: float with diameter of circumscribing circle, i.e. the circle that all the polygon's corners lie on.
n_vertices: int with number of corners of this polygon. Three for a triangle, four for a square, five for a pentagon etc.

ApertureMacroInstance

One instance of an aperture macro. An aperture macro defined with an AM statement can be instantiated by multiple AD aperture definition statements using different parameters. An ApertureMacroInstance is one such binding of a macro to a particular set of parameters. Note that you still need an ApertureMacroInstance even if your ApertureMacro has no parameters since an ApertureMacro is not an Aperture by itself.

Attributes:

Common attributes:: unit, attrs, original_number, and rotation. ApertureMacroInstance does not support hole_dia or hole_rect_h. rotation is handled by re-writing the ApertureMacro during export.
macro: The ApertureMacro that is bound here
parameters: list of ints or floats with the parameters for this macro. The first element is $1, the second is $2 etc.

ExcellonTool

Special Aperture subclass for use in ExcellonFile. Similar to CircleAperture, but does not have hole_dia or hole_rect_h, and has additional plated and depth_offset attributes.

Common attributes:: unit, original_number
plated: bool or None. True if this hole/slot is copper-plated, False if not, and None if it is undefined or unknown.
depth_offset: float with Excellon depth offset for this hole or slot. If the fab supports this, this can be used to create features that do not go all the way through the board.

Aperture generalization

Gerbonara supports rotating both individual graphic objects and whole files. Alas, this was not a use case that was intended when the Gerber format was developed. We can rotate lines, arcs, and regions alright by simply rotatint all of their points. Flashes are where things get tricky: Individual flashes cannot be rotated at all in any widely supported way. There are some newer additions to the standard, but I would be surprised if any of the cheap board houses understand those. The only way to rotate a flash is to rotate the aperture, not the flash. For cirlces, this is a no-op. For polygons, we simply change the angle parameter. However, for rectangles and obrounds this gets tricky: Neither one supports a rotation parameter. The only way to rotate these is to convert them to an aperture macro, then rotate that.

This behavior of using aperture macros for general rotated rectangles is common behavior among CAD tools. Gerbonara adds a non-standard rotation attribute to all apertures except CircleAperture and transparently converts rotated instances to the appropriate ApertureMacroInstance objects while it writes out the file. Be aware that this may mean that an object that in memory has a RectangleAperture might end up with an aperture macro instance in the output Gerber file.

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