Sketcher reference/en

Introduction
User wrote a lengthy 70-page reference manual for the Sketcher Workbench that covers many topics of using this workbench. For inexperienced users, it is a gentle introduction that covers the basic usage of the Sketcher, and then goes into many details of creating geometrical elements, and using each type of constraint.

The manual is a work in progress, as some sections are reviewed and updated depending on the development occurring on the Sketcher Workbench. The original manual was written for FreeCAD 0.17, and it has since been updated for 0.18. The latest manual can be found in the forum thread, Sketcher tutorial.



Contents
The general structure of the manual is:
 * Basics
 * Create a sketch
 * The Sketcher window
 * General remarks on degrees of freedom
 * Auto constraints
 * Geometric elements
 * Common usage
 * Line
 * Circle
 * Arc
 * Polyline
 * Rectangle
 * Polygon
 * Slot
 * B-splines
 * Conical sections
 * Construction geometry
 * Point
 * Constraints
 * Selecting constraints
 * Applying constraints
 * The solver
 * Coincidence
 * Point on object
 * Vertical
 * Horizontal
 * Parallel
 * Perpendicular
 * Tangency
 * Equality
 * Symmetry
 * Block
 * Lock
 * Horizontal distance
 * Vertical distance
 * Length
 * Radius and diameter
 * Angle
 * Dos and don'ts with constraints
 * External geometry
 * Creating objects based on sketches
 * Sketches for pads
 * Symmetry
 * Placement and attachment offset
 * Validate sketches