1. University of Maribor 1 CADUI'96 - 5-7 June 1996 - FUNDP Namur An Interactive Constraint-Based Graphics System with Partially Constrained Form-Features Borut Zalik Laboratory for Computer Graphics & Artificial Intelligence Faculty of Electrical Engineering & Computer Science MARIBOR (Slovenia)

2. University of Maribor 2 CADUI'96 - 5-7 June 1996 - FUNDP Namur Introduction Problems which exist at the input of geometric modelling systems: the designers still have to use the most primitive approach of 'trials and errors' the engineering vocabulary is not supported spatial relationships cannot be expressed. Two promissing approaches: constrained-based and feature-based design of geometric objects

3. University of Maribor 3 CADUI'96 - 5-7 June 1996 - FUNDP Namur 2D interactive constraint-based drawing system is considered. self-evident fact about geometric object are extracted automatically initial approximate data are used in the case of underdimensioning geometric constraints are specified in an interactive way.

4. University of Maribor 4 CADUI'96 - 5-7 June 1996 - FUNDP Namur geometry is divided into two groups –visible geometry (related with topology) –auxiliary geometry (related with geometric constraints).

5. University of Maribor 5 CADUI'96 - 5-7 June 1996 - FUNDP Namur Constraints refer only to the auxiliary geometry (points, lines, and circles).

6. University of Maribor 6 CADUI'96 - 5-7 June 1996 - FUNDP Namur Constraints A constraint describes a relation that should be satisfied. Structural constraints Through (l i, p j )line l i passes through point p j HLine (l i )line l i is horizontal Parallel (l i, l j )lines l i and l j are parallel Dimensional constraints Distance (p i, p j, d)distance between points p i and p j is d Angle (l i, l j,  )angle between lines l i and l j is  Numerical constraints

7. University of Maribor 7 CADUI'96 - 5-7 June 1996 - FUNDP Namur Problems at constraint description An efficient constraint solver has to be implemented. Inserting exact number of constraints. In real applications a huge number of constraints have to be specified. Constraining of free-form shapes is usually not considered.

8. University of Maribor 8 CADUI'96 - 5-7 June 1996 - FUNDP Namur Constraint Solving A local propagation of known states –supports an interactive design –easy to implement. An implementation with BCDG.

9. University of Maribor 9 CADUI'96 - 5-7 June 1996 - FUNDP Namur Form-Features A form-feature is a group of geometric and topolo- gical entities with functional meaning in a certain context. Parametrisation of a form-feature can be different.

10. University of Maribor 10 CADUI'96 - 5-7 June 1996 - FUNDP Namur Solutions: more than one constraining schemes is prepared transformation algorithms are used. Our approach: The form-features are not constrained completely at the time of forming but during the process of combining of individual form-features.

11. University of Maribor 11 CADUI'96 - 5-7 June 1996 - FUNDP Namur

12. University of Maribor 12 CADUI'96 - 5-7 June 1996 - FUNDP Namur Interactive Constraining Process An untrained user describes the serif as a feature having three line segments and two curves. Conclusion: The user describes the visible geometry. Description does not include spatial relations.

13. University of Maribor 13 CADUI'96 - 5-7 June 1996 - FUNDP Namur The actions of the designer are observed by the system to generate all self-evident facts. Which facts are self-evident? Should we used an automatic detection of constraints based on the "small number  "?

14. University of Maribor 14 CADUI'96 - 5-7 June 1996 - FUNDP Namur Demonstration of our system

15. University of Maribor 15 CADUI'96 - 5-7 June 1996 - FUNDP Namur

16. University of Maribor 16 CADUI'96 - 5-7 June 1996 - FUNDP Namur

17. University of Maribor 17 CADUI'96 - 5-7 June 1996 - FUNDP Namur

18. University of Maribor 18 CADUI'96 - 5-7 June 1996 - FUNDP Namur

19. University of Maribor 19 CADUI'96 - 5-7 June 1996 - FUNDP Namur

20. University of Maribor 20 CADUI'96 - 5-7 June 1996 - FUNDP Namur

21. University of Maribor 21 CADUI'96 - 5-7 June 1996 - FUNDP Namur Conclusions The system distinguishes between auxiliary and visible geometry By observing the actions of designer the self- evident information is extracted Bézier cubics are constrained in a natural way. Well-constrained and under-constrained objects are handled.

22. University of Maribor 22 CADUI'96 - 5-7 June 1996 - FUNDP Namur

23. University of Maribor 23 CADUI'96 - 5-7 June 1996 - FUNDP Namur