Sketching

A free-form application - Sketcher - is an integral component of any modern CAD. Any 3D construction based on standard features usually starts with setting a 2D profile. A 2D profile comprising nodes (points), connected to each other with edges (segments and circular arcs or other curves), is an example of a standard parametric feature. Every profile feature has its own parameters. In traditional parametric systems (based on the constructing history), the profile form is controlled by changing the parameters of its elements (nodes and arcs). Variational sketch drawing has an essential advantage in comparison with the described approach: at any moment designers can add or remove any logic (incidence, parallelism, tangency) or parametric (arc radius, length of a segment, distance) constraint between geometric line elements. In this case the system automatically changes the form of profile (by selecting new parameter values for the profile elements) to conform to all imposed constraints. Another advantage of variational approach to sketching is diagnostic of sketching elements (in order to determine the excess or incompatible constraints, as well as identify the remaining degrees of freedom). Furthermore, users have a tool for dynamic relocation (with the «mouse» manipulator) of geometric profile elements along such trajectories where all given constraints are not violated. An important auxiliary functionality of sketching applications is automated imposing of constraints upon the elements, which enables removing all remaining degrees of freedom to fully control the profile form by changing constraint parameters.