About LGS 2D                  About LGS 3D

LGS 2D is a computational module engineered to support two-dimensional parametric sketching/drawing in CAD and computer graphics systems, as well as any other application that requires parametric connections or constraints to be set between geometrical objects.

LGS 2D supports creation and modification of the geometric models by means of (explicit or implicit) constraints. Typical geometric objects are points, lines, circles, or black-box parametric curves. Objects can be fixed in the absolute coordinate system or with respect to each other (the latter feature is provided by the so-called rigid sets of objects). A set of geometric constraints includes logical constraints between geometric entities (like coincidence, parallelism, tangency, etc.), and dimensional constraints (that specify the required values for the given distances, angles or radii). LGS 2D also supports user-defined variables, algebraic and black-box equations, and tabular constraints that can be arbitrarily mixed with geometric dimensions. LGS 2D moves and rotates objects to positions where all constraints are satisfied with minimal possible transformations of the initial configuration. LGS 2D is a simultaneous solver: it can solve cyclic dependencies between constraints. Both under-constrained and over-constrained models can be efficiently solved. Additional features of LGS 2D are dynamic constraint solving (while dragging an object) and redundant/inconsistent constraint diagnostics.

LGS 2D is a cross-platform software package. It is a set of binary libraries that runs under all 32- and 64-bit Windows, Linux, *BSD, AIX, HP-Unix, Sun Solaris, MacOS and other OS. Coded in C++, LGS 2D has an API declared in pure C to be integrated into a broad range of software applications. LGS 2D can be used as a self-supporting component, or jointly with LGS 3D version. Both 2D and 3D versions have similar API, providing a complete parametric solution for all aspects of CAD/CAM/CAE system functionality - from 2D sketching to history-free parametric 3D modeling, assembly design, kinematic simulation, etc.

A sample sketching application called Lege'n'd 2D is available as a free download at the LEDAS web site with a set of representative examples of different industrial sketches. This application can be used by anyone to test functionality, robustness and performance of LGS 2D. It was created with the Open CASCADE open-source application framework. The source code of Lege'n'd 2D is available under special request.

Current version is LGS 2D 6.0

LGS 2D 6.0 implements segments and arcs as new types of entities. Jointly, they are known as edges. Edges can be interpreted as new kinds of geometric objects and as ternary constraints. (The latter means that each edge is created on top of three LGS2D objects — a line, circle, or ellipse, and two points — and then imposes two coincidence constraints between the first object and each point.)

In addition, the endpoints of edges keep their order during the constraint solving process. For segments, this means that the direction of lines is always oriented from the first to the second end point. (This direction can be reverted by modifying the edge’s alignment attribute.)

Each edge also has a length attribute, with values of free, fixed, or linked to a variable. Circular and elliptic arcs have the angle attribute with the same properties. Through edges, any LGS-based application can provide users with full parametric control over their drawings, which is unreachable when the geometry is modeled with unbounded objects (i.e., lines, circles, ellipses) that are connected with two incident points. See example below.

Edges also represent a special case of dependent curves with three control objects. This means that they can be linked with other geometries using the appropriate constraints, such as incidence with a point, and tangency to a line. For example, when users set the incidence constraint between a point and a segment, then the point will always lie between the segment's endpoints. This is behavior that cannot be modeled with unbounded geometry.

Edges are implemented as a new add-on module for LGS 2D named LGSProfiles. Programmers can use edges in the same way as they do other LGS 2D objects. In the future, LEDAS plans to extend the LGSProfiles module with other bounded geometries, such as composite and offset curves.

Version 6.0 produces more natural solutions for several constraint scenarios. The solver implemented two new techniques to minimize changes to the model, and to keep the sketch as close as possible to the initial drawing. These techniques work effectively for scenarios with one to three unsatisfied constraints, which are typical for interactive sketcher applications.

For the full list of changes see Release Status page.