Sketch-based Interface for 3d Parametric Modelling

In this paper we present an experimental prototype called GEGROSS (GEsture & Geometric ReconstructiOn based Sketch System). This application allows using freehand sketches to create 3D parametric models onto a Tablet-PC. The modelling process consists of two stages. First, the user introduces the geometry of the 2D section using continuous sketches composed by line segments, circles and arcs, and then he can add, delete or edit the dimensional and geometric constraints by means a gesture alphabet (a gesture in this context represents a graphical symbol that is translated into a command). The supported gestures are geometry (line, arc, circle or ellipse), or constraint (dimension, parallel, perpendicular, tangent, concentric, horizontal or vertical). Later, in the second stage and also using gestures it is possible to make an extrusion or a revolution of the parametric section generated in the previous stage to create a 3D model. Then this process can continue, sketching new 2D sections onto the faces of the generated object and applying the corresponding modelling gestures. The application uses the geometric kernel ACIS to store geometric entities, and the 2D DCM constraint manager from UGS D-Cubed firm to manage geometric and dimensional constraints of the parametric sections. Preliminary tests have concluded the GEGROSS application is a feasible alternative to current approach used in commercial CAD applications in order to create shapes of small or medium complexity. In that situation it presents a more effective modelling time, and it has been rated as easier to learn than comparable commercial applications.