Warning : work in progress. Early stage of development
Osvcad is a CAD system that models systems using Acyclic Directed Graphs of heterogeneous geometrical entities.
If installing on Linux, make sure that glxgears (just type glxgears at the prompt) display its 3 gears !
The recommended way to install osvcad uses Docker and is explained in INSTALL.rst
The geometry of a product in Osvcad is handled by 2 classes: PartGeometryNode and AssemblyGeometryNode (see nodes.py).
Both PartGeometryNode and AssemblyGeometryNode inherit from GeometryNode which is an abstract class used to define a common interface. In addition, AssemblyGeometryNode inherits from networkx.DiGraph. The consequence is that AssemblyGeometryNode can contain a graph and be a node of a graph of GeometryNode(s) at the same time.
Fig. 1 : Class diagram for geometry nodes
A PartGeometryNode can be created from a variety of sources (a STEP file, a STEPZIP file, a specifically formatted Python script/module or a Library part). An AssemblyGeometryNode is created by defining the PartGeometryNode(s) that compose it and the positioning relationships between the PartGeometryNode(s).
stepzip files are zip files containing a STEP file and a *.anchors file. The *.anchors file specifies where the anchors are on the STEP file. It is a convenient way to store and use a STEP file with its logical anchors in a single file that can be used to create a PartGeometryNode. Any unzipping utility can be used to view its content. In Osvcad, the stepzip files are handled by the stepzip.py module.
A single part is normally designed in its own frame of reference, usually near the origin where x, y and z are 0. To define an assembly, we need a way to express that "part A's bottom goes on top of part B". This is why Oscad uses a system of anchors. An anchor is made of a point and a direction (i.e. an attached vector); the anchors on parts are chosen to be functionally meaningful (e.g. the exit of a hole in a part, the center of the bottom of the head on a screw ....). By expressing how 2 anchors on different parts should be positioned relative to each other, it is possible to position the parts in an assembly.
The relative positioning of 2 parts in an assembly is the object contained by an edge of the graph representing the assembly. This object is a Constraint (see edges.py). Constraint is an abstract class that defines the minimum set of methods that all constraints should implement (actually, a single transform() method). Osvcad currently implements the ConstraintAnchor constraint that positions 2 anchors opposite to each other while allowing a rotation and a translation aound/on the axis defined by the now colinear anchors. It is planned to implement more types of constraints.
Fig. 2 : Class diagram for graph edges/constraints
As an illustration of how the ConstraintAnchor works, here is a very simple example. 2 cubes (red and green) each define 1 anchor (the yellow arrows). The blue cube is a result of positioning the green cube on the red cube using their anchors:
To be completed