Package layout

Five namespaces, ten classes and one middle layer: how the parts of drafting are arranged, and how an object made in one part becomes an object of another.

Five namespaces around one middle layer

Every public name in the package lives in one of five namespaces. +geom sits in the middle and the other four build on it: a solid is made from regions and cut back into regions, a mesh is cut into regions, and a drawing is made of geom objects. +geom depends on none of them, so a solid never depends on the drawing model, and the drawing model never depends on Open CASCADE.

Below them, in src, five compiled files do the heavy work. None of them is called directly; each is reached through the classes and functions above.

Open CASCADE 7.8 or later, its visualization libraries and X11 are needed to build the package; pkg install stops and names what is missing.

Rules that hold everywhere

• Objects are values. Every class except model.Viewer is a value class: a method returns a new object and leaves the one it was given unchanged, so a result is always assigned, S = fillet (S, E, 2). A viewer is a handle, because it stands for a window.
• Functions take objects. Only constructors take plain matrices. The planar geometry functions of +geom that work on point sets carrying no arcs, such as geom.offset or geom.curvature, take N-by-2 matrices, as before.
• Lengths are millimetres and angles are degrees, everywhere and in every file the package writes.
• Pieces come back as a row cell of regions. Region booleans, offset, section, projection and geom.text can give several separate pieces, so they return a row cell array of geom.Region objects, largest first, and cell (1, 0) when nothing is left.
• Reading is a function, writing is a method. A file is read by a function in the namespace of what it returns (solid.read, polymesh.read, model.read, geom.read, draw.read) and written by the write method of the object written, which picks the format from the file's extension.

The geometry classes

Four value classes are the package's one representation of outlines and curves, used by drawings and solids alike. Each lies in a geom.UCS, the world xy plane unless told otherwise.

A region is the hub of the package. It is what a solid is made from, what a section of a solid or a mesh is, what geom.text gives and what a hatch fills. It combines with union, subtract and intersect, grows and shrinks with offset, rounds and bevels with fillet and chamfer, and is wrapped by hull, resized, mirrored and copied in rows, columns or round a point.

The UCS, the frame they share

A geom.UCS is a user coordinate system: an origin, an x axis and a normal, so a plane with coordinates of its own. It is how the namespaces agree on where things are. Assigning a geom object another UCS moves it there, keeping its shape in its own coordinates, so a profile drawn in the xy plane is laid on any face of a part by giving it that face's UCS.

A UCS is made from a normal and an origin, geom.UCS (NORMAL, ORIGIN), with a point the x axis points to as a third argument, or from three points with geom.UCS.threepoint. geom.UCS () is the world xy plane. toworld and tolocal carry points between a UCS and the world.

From one class to another

Every way an object of one class becomes an object of another:

One object through every layer

A plate with a bore, made once as a region and carried through the package:

## A plate 60 by 40 with a bore of diameter 20, in the xy plane
R = geom.Region ([0, 0; 60, 0; 60, 40; 0, 40], {[20, 20, 1; 40, 20, 1]});

## A solid from the region, and a mesh from the solid
S = solid.extrude (R, 10);
M = tessellate (S);

## A cut through the middle of the bore gives two pieces, each a region
## lying in the plane of the cut
C = section (S, geom.UCS ([0, -1, 0], [0, 20, 0]));

## A drawing is flat, so lay a piece in the xy plane before hatching it
Q = C{1};
Q.UCS = geom.UCS ();
D = draw.Drawing ('section');
D = D.hatch (Q);

## The plate twice in an assembly, the second stacked on the first
A = model.Assembly ('stack');
A = add (A, 'plate', S, geom.UCS ());
A = add (A, 'plate', [], geom.UCS ([0, 0, 1], [0, 0, 10]));

The second add passes [] for the part: the part named 'plate' is already defined, so the assembly places it again rather than storing it twice.

Files

How each geom class and each drawing entity is written to DXF and read back is set out in DXF and the classes.