Sketcher Dialog
Introduction
While a sketch is being edited, or, in other words, while a sketch is in edit mode, the Sketcher Dialog is displayed on the Task tab of the Combo view.
To put a sketch in edit mode do one of the following:
 Doubleclick the sketch in the Tree view.
 Rightclick the sketch in the Tree view and select Edit sketch from the context menu.
 Select the sketch and press the Edit sketch button.
 Select the sketch and then select the Edit sketch option from the menu.
The dialog consists of the following sections:
Solver messages
This section informs about the state of the sketch. A sketch can be under constrained, fully constrained or have redundant constrains.
If a sketch is under constrained the number of degrees of freedom (or Dofs) is indicated. Clicking this text will select the under constrained sketch elements.
If a sketch has redundant constraints the indices of the constraints are indicated. Clicking that text will select these constraints.
Available options:
Option  Description 

This button opens a menu:

Advanced solver control
This section will only appear if you check the Show section 'Advanced solver control' option in the sketcher preferences.
Note that most of the options in this section are of no practical use. They can however help with testing and understanding the solvers.
Available options:
Option  Description 

Default solver  The solver that is used for solving the geometry. LevenbergMarquardt and DogLeg are trust region optimization algorithms. The BFGS solver uses the Broyden–Fletcher–Goldfarb–Shanno algorithm. 
DogLeg Gauss step  This setting is only available for the solver DogLeg. It is the step type used in the DogLeg algorithm. 
Maximum iterations  If the solver needs more iterations to find a convergence to a solution, it will stop and output that it failed. 
Sketch size multiplier  If checked, the maximum iterations will be multiplied by the number of parameters. The idea is that bigger sketches would need more iterations to converge. 
Convergence  The threshold for the squared error. This error is used to determine whether a solution converges or not. 
Eps/Eps1/Tau  These settings are only available for the solver LevenbergMarquardt. You should only change something here if you fully understand how the LevenbergMarquardt solver works. 
Tolg/Tolx/Tolf  These settings are only available for the solver DogLeg. You should only change something here if you fully understand how the DogLeg solver works. 
QR Algorithm  During diagnosing the rank of the matrix is calculated which enables to further analyze the constraint system to determine if there are redundant/conflicting constraints. The rank revealing decomposition used in FreeCAD is QR. There are two algorithms: Eigen Dense QR is a dense matrix QR with full pivoting, which is the legacy proven algorithm that works very well but it is rather slow as the system grows. The Eigen Sparse QR algorithm is an optimization for sparse matrices (having lots of zeros), which is usually much faster, since FreeCAD's systems do have a lot of zeros. 
Pivot threshold  When doing a QR, values under the pivot threshold are treated as zero. 
Redundant Solver  The solver that is used during diagnosing to determine whether a group is redundant or conflicting. 
Red. Max Iterations  The same as Maximum iterations, but for the redundant solving. 
Red. Sketch size multiplier  The same as Sketch size multiplier, but for the redundant solving. 
Red. Convergence  The same as Convergence, but for the redundant solving. 
R.Eps/R.Eps1/R.Tau  The same as Eps/Eps1/Tau, but for the redundant solving. 
R.Tolg/R.Tolx/R.Tolf  The same as Tolg/Tolx/Tolf, but for the redundant solving. 
Console Debug mode  Setting to specify the verbosity of the console output. 
Solve  This button explicitly starts the solver. 
Restore Defaults  This button restores the default solver settings. 
Constraints
This section lists the constraints in the sketch. Unchecking a constraint in the list will hide it in the sketch. Constraints can be selected in the list as well as in the sketch.
Available options:
Option  Description 

Filter  If the Filter checkbox is checked the Filter dropdown list controls which constraints are listed:

This button toggles the visibility of the listed constraints in the sketch.  
This button opens a menu:
 
Context menu  Rightclicking constraints selected in the list opens a context menu. The menu has the following options:

Elements
This section lists the elements in the sketch. Unchecking an element in the list will hide it in the sketch. Elements can be selected in the list as well as in the sketch.
Available options:
Option  Description 

Filter  If the Filter checkbox is checked the Filter dropdown list controls which elements are listed:

This button opens a menu:
 
Each element in the list has 1 to 4 buttons organized in 4 columns. These select a specific part of the element. Only applicable buttons are shown.
Clicking the text has the same effect as clicking the first available button of the element.  
Context menu  Rightclicking elements selected in the list opens a context menu. The menu contains the Geometric constraint tools, the Dimensional constraint tools and the following additional options:

 General: Create sketch, Edit sketch, Map sketch to face, Reorient sketch, Validate sketch, Merge sketches, Mirror sketch, Leave sketch, View sketch, View section, Toggle grid, Toggle snap, Configure rendering order, Stop operation
 Sketcher geometries: Point, Line, Arc, Arc by 3 points, Circle, Circle by 3 points, Ellipse, Ellipse by 3 points, Arc of ellipse, Arc of hyperbola, Arc of parabola, Bspline by control points, Periodic Bspline by control points, Bspline by knots, Periodic Bspline by knots, Polyline, Rectangle, Centered rectangle, Rounded rectangle, Triangle, Square, Pentagon, Hexagon, Heptagon, Octagon, Regular polygon, Slot, Fillet, Cornerpreserving fillet, Trim, Extend, Split, External geometry, Carbon copy, Toggle construction geometry
 Sketcher constraints:
 Geometric constraints: Coincident, Point on object, Vertical, Horizontal, Parallel, Perpendicular, Tangent, Equal, Symmetric, Block
 Dimensional constraints: Lock, Horizontal distance, Vertical distance, Distance, Radius or weight, Diameter, Auto radius/diameter, Angle, Refraction (Snell's law)
 Constraint tools: Toggle driving/reference constraint, Activate/deactivate constraint
 Sketcher tools: Select unconstrained DoF, Select associated constraints, Select associated geometry, Select redundant constraints, Select conflicting constraints, Show/hide internal geometry, Select origin, Select horizontal axis, Select vertical axis, Symmetry, Clone, Copy, Move, Rectangular array, Remove axes alignment, Delete all geometry, Delete all constraints
 Sketcher Bspline tools: Show/hide Bspline degree, Show/hide Bspline control polygon, Show/hide Bspline curvature comb, Show/hide Bspline knot multiplicity, Show/hide Bspline control point weight, Convert geometry to Bspline, Increase Bspline degree, Decrease Bspline degree, Increase knot multiplicity, Decrease knot multiplicity, Insert knot, Join curves
 Sketcher virtual space: Switch virtual space
 Additional: Sketcher Dialog, Preferences, Sketcher scripting
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