Varkon Geometry Tutorial: Coordinate Systems 2006-03-12

Coordinate Systems

Please refer to the
Varkon Users Manual: mode_global, mode_local and mode_basic
Varkon Users Manual (MODULE type and attribute): LOCAL, GLOBAL, BASIC
Varkon Programmers Manual: mode_global, mode_local, mode_basic, csys_1p and csys_3p
Varkon Programmers Manual (MODULE, keywords and identifiers): Attributes LOCAL, GLOBAL, BASIC

All objects in CAD systems should be defined in named coordinate systems!
Many real objects (subassemblies/parts) are defined in local system, and this is a good idea. A definition (local) coordinate system for an object can optimally be chosen, the coordinates need not to be big, etc.
Unfortunately many objects are defined in a CAD systemís basic coordinate system, i.e. the position is un-defined relative other objects in an assembly. An import/export function (or a user must manually) transformate the object to the right position, and there is a risk for mistakes.
With Varkon there are many options to get a good and safe handling of coordinate systems. Many of the requirements on coordinate systems originally came from Saab Aircraft.


Saab Aircraft defines hundreds of coordinate systems in an aircraft project. It is a tree of coordinate systems where each coordinate system (child) is defined relative a parent coordinate system.

Coordinate System Tree

In an assembly model can the coordinate systems first be defined and then are all the LOCAL modules (subassemblies/parts) created.

Assembly based on local csys

Lower level modules are normally GLOBAL. The module should inherit the active coordinate system from its parent. Sometimes, for instance for planar sections curves may LOCAL be a good alternative.
Very few modules shoul be (are) BASIC. Exceptions could be for some curves, like for instance a P-value curve for a Conic Lofting Surface. This curve shall be defined in the basic coordinate system.

Lower level modules

When I look at all my applications I realize that I also have created very few LOCAL modules. Instead are mode_local, mode_basic and mode_global called inside the model.

Inside module

When a local coordinate system is made active (with mode_local), immediately change back to the global (inherited, input) coordinate system (with mode_global), when the local system system no longer is used.

No samples for coordinate systems