Currently I am doing a master thesis regarding geometric and parametric constraints similar to the ones that can be found in Autocad. There are a few modifications, but in general I would like to compare them with what is currently in Autocad. Could anyone point me out where those constraints are actually stored? I have searched through the DXF and DWG specs, but couldn't find the reference.
I would also like to know if constraints in Autocad are 'metainformation' along with a materilised shape or actually the base of the shape that is resolved, and is materialised each time a constraint changes.
AutoCAD isn't a fully constraint based parametric modeler like Inventor is. So to reuse your own words, constraint are 'metainformation' along with the materilised shape. They apply to sub-entity edges and vertices of the AutoCAD geometry.
To get an idea about how and where constraints are store inside a dwg database, the best is probably to take a look at the associative framework topic that is describe in details inside the ObjectARX SDK API Help Files. You will find there the relevant concepts and objects involved in the parametric behavior added to AutoCAD.
I also attach a sample ARX project that we created, entitled ArxConstrainDbg, by analogy to ArxDbg, which allows to dump existing constraints from a dwg.
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