(b) 3D model
The 3D model is the core of the entire CAD system and is the hub for connecting the various modules. An abstract description of a part of a computer language. The information that the 3D model needs to record is divided into the following categories:
Geometric information: record the spatial position of the part;
Assembly information: record the assembly relationship between parts and other parts;
Production information: record processing information of parts, such as size;
Drawing information: Explain how the part expresses itself on the drawing.
The 3D model is not only the recorder of information, but also the maintainer of information. There is a complex constraint relationship between various kinds of information, and the maintenance of consistency between them is naturally taken care of by the three-dimensional model. For example, when the user changes the position of a view in the component on the drawing, the other two views must also be modified accordingly, which must be done by maintaining the consistency of the drawing information and the geometric information. For example, when the position or size of a part changes, the parts with which it is assembled must also be modified to maintain the assembly relationship. This necessitates maintaining the consistency of assembly information and production information. The following is an example of a simplified angle iron object to illustrate the design of an angular iron three-dimensional model:
Class JT
{
Geometric information:
Point1, Point2: The position of the two anchor points in the space in the space Rotation: the angle of rotation of the angle iron in the space Assembly information:
HeadID, TailID: ID number of the angle iron connected to the corner iron joint JointIDArray: ID number sequence of the angle iron connected to the middle of the angle iron Production model:
Width, Length, Thick: The three most basic size parameters of the angle iron, width, length and thickness. Drawing information:
ViewID[3]: ID number of the three views of the angle iron (top view, top view, left view). Operation of maintaining geometric information and drawing information:
TranslateViewToModal(): converts a point in the model to a plane point in a view TranslateModalToView(): converts a point in the view into a 3D space point ...
}
(c) Expression of assembly relationship
The assembly relationship between components can be abstracted by the association, inheritance, and containment between objects. The connection relationship between the angle irons is an association, and the relationship between the chamber and the angle iron is tolerance and the like.
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