Sketcher ConstrainCoincident: Difference between revisions

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<languages/>
<languages/>
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<!--T:37-->
{{Docnav
{{Docnav
|[[Sketcher_ToggleConstruction|Construction Mode]]
|[[Sketcher_ToggleConstruction|Construction Mode]]
|[[Sketcher ConstrainPointOnObject|Point On Object]]
|[[Sketcher_ConstrainPointOnObject|Point On Object]]
|[[Sketcher_Workbench|Sketcher]]
|[[Sketcher_Workbench|Sketcher]]
|IconL=Sketcher_ToggleConstruction.svg
|IconL=Sketcher_ToggleConstruction.svg
|IconC=Workbench_Sketcher.svg
|IconR=Constraint_PointOnObject.svg
|IconR=Constraint_PointOnObject.svg
|IconC=Workbench_Sketcher.svg
}}
}}


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{{GuiCommand
{{GuiCommand
|Name=Sketcher ConstrainCoincident
|Name=Sketcher ConstrainCoincident
|Icon=Constraint_PointOnPoint.svg
|Workbenches=[[Sketcher Workbench|Sketcher]]
|Shortcut={{KEY|C}}
|MenuLocation=Sketch → Sketcher constraints → Constrain coincident
|MenuLocation=Sketch → Sketcher constraints → Constrain coincident
|Workbenches=[[Sketcher_Workbench|Sketcher]]
|SeeAlso=[[Sketcher_ConstrainLock|Constrain Lock]], [[Sketcher ConstrainPointOnObject|Constrain Point onto Object]]
|Shortcut={{KEY|C}}
|SeeAlso=[[Sketcher_ConstrainLock|Sketcher Constrain Lock]], [[Sketcher_ConstrainPointOnObject|Sketcher Constrain Point onto Object]]
}}
}}


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<!--T:3-->
As stated above, this tool takes two arguments - both are points.
As stated above, this tool takes two arguments - both are points.
# First, it is necessary to highlight two distinct points. ({{Emphasis|Note:}} this will not work if, for example, you attempt to select the start and end point of the same line).
# First, it is necessary to highlight two distinct points. ({{Emphasis|Note:}} this will not work if, for example, you attempt to select the start and end point of the same straight line; selecting the start and end points of an arc will produce a closed circle or ellipse but will constrain the location of the seam to be on that point).
# Highlighting of a drawing item is achieved by moving the mouse over the item and clicking the left-mouse-button.
# Highlighting of a drawing item is achieved by moving the mouse over the item and clicking the left-mouse-button.
# It is also possible to highlight all items inside a rectangle by clicking and dragging. When dragging from left to right (with any vertical motion), only the shapes which are entirely contained within the rectangle will be highlighted; in the other direction all shapes which intersect with the selection rectangle will be highlighted. This can be used to select only the vertices without selecting the edges, by dragging a small recangle around some vertices from left to right, as long as there are no edges which are fully contained within the rectangle.
# A highlighted item will change its color to green. (This color can be customized in {{MenuCommand|Editing → Preference → Display → Colors → Selection}})
# A highlighted item will change its color to green. (This color can be customized in {{MenuCommand|Editing → Preference → Display → Colors → Selection}})
# Subsequent items can be highlighted by repeating the above procedure(s). {{Emphasis|Note:}} it's unnecessary to hold-down any special key like {{KEY|Ctrl}} to achieve multiple item selection in a drawing.
# Subsequent items can be highlighted by repeating the above procedure(s). {{Emphasis|Note:}} it's unnecessary to hold-down any special key like {{KEY|Ctrl}} to achieve multiple item selection in a drawing.
# Once you have two points highlighted, you can invoke the command using several methods:
# Once you have two points highlighted, you can invoke the command using several methods:
#* Pressing on the {{Button|[[Image:Constraint_PointOnPoint.svg|24px]] [[Sketcher_ConstrainCoincident|PointOnPoint]]}} constraint button in the toolbar.
#* Pressing on the {{Button|[[File:Sketcher_ConstrainCoincident.svg|16px]] [[Sketcher_ConstrainCoincident|Coinstrain coincident]]}} constraint button in the toolbar.
#* Using the {{KEY|C}} keyboard shortcut.
#* Using the {{KEY|C}} keyboard shortcut.
#* Using the {{MenuCommand|Sketch → Sketcher constraints → Constrain coincident}} entry in the top menu.
#* Using the {{MenuCommand|Sketch → Sketcher constraints → Constrain coincident}} entry in the top menu.
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{{Emphasis|Note:}} In order to make two points coincident, FreeCAD must out of necessity move one (or both) of the original points.
{{Emphasis|Note:}} In order to make two points coincident, FreeCAD must out of necessity move one (or both) of the original points.


==Scripting== <!--T:8-->
== Alternatives to Coincident constraint == <!--T:42-->

<!--T:43-->
The two constrained items of a [[Sketcher_ConstrainCoincident|Coincident]] constraint must be start point or end point vertices, or center points of arcs, circles or ellipses. Some combinations which are not possible with a coincident constraint can be emulated using other constraints:
* The [[File:Sketcher_ConstrainSymmetric.svg|24px]] [[Sketcher_ConstrainSymmetric|Symmetric]] constraint can be used to place a start point, end point or center point on the midpoint of a straight line.
* A midpoint-to-midpoint placement of two straight lines can be achieved by creating a new [[File:Sketcher_CreatePoint.svg|24px]] [[Sketcher_CreatePoint|Point]] and using two [[File:Sketcher_ConstrainSymmetric.svg|24px]] [[Sketcher_ConstrainSymmetric|Symmetric]] constraints so that it lies on the midpoint of both lines.
* A vertex can be constrained to lie along an edge using a [[File:Sketcher_ConstrainPointOnObject.svg|24px]][[Sketcher_ConstrainPointOnObject|PointOnObject]] constraint. Note that with this constraint, the point can lie anywhere on the full extension of a segment or curve (i.e. also before the start point or beyond the end point).
* A collinear placement of two straight lines can be obtained by applying a [[File:Sketcher_ConstrainTangent.svg|24px]] [[Sketcher_ConstrainTangent|Tangent]] constraint to them, or by combining a [[File:Sketcher_ConstrainPointOnObject.svg|24px]] [[Sketcher_ConstrainPointOnObject|PointOnObject]] constraint and a [[File:Sketcher_ConstrainParallel.svg|24px]] [[Sketcher_ConstrainParallel|Parallel]] constraint.
* Two edges can be made identical by using two [[File:Sketcher_ConstrainCoincident.svg|24px]] [[Sketcher_ConstrainCoincident|Coincident]] constraints, one for each pair of extremities.
* Two circles can be made identical by using a [[File:Sketcher_ConstrainCoincident.svg|24px]] [[Sketcher_ConstrainCoincident|Coincident]] constraint to merge the centers, and applying an [[File:Sketcher_ConstrainEqual.svg|24px]] [[Sketcher_ConstrainEqual|Equal]] constraint to their edges. For arcs, this will ensure both arcs are part of the same circle, while allowing them to have different start and end points.

==Scripting== <!--T:14-->

<!--T:44-->
The constraint can be created from [[Macros|macros]] and from the [[Python|Python]] console by using the following command:


===General scripting=== <!--T:14-->
The constraint can be created from macros and from the python console by using the following command:
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</translate>
{{Code|code=Sketch.addConstraint(Sketcher.Constraint('Coincident',LineFixed,PointOfLineFixed,LineMoving,PointOfLineMoving)) }}
{{Code|code=Sketch.addConstraint(Sketcher.Constraint('Coincident',LineFixed,PointOfLineFixed,LineMoving,PointOfLineMoving)) }}
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<translate>

<!--T:9-->
<!--T:9-->
where :
where :
* {{incode|Sketch}} is a sketch object
* {{incode|Sketch}} is a sketch object
* {{incode|LineFixed}} is the number of the line, that will not move by applying the constraint
* {{incode|LineFixed}} is the number of the line, that will not move by applying the constraint
* {{incode|PointOfLineFixed}} is the number of the vertex of the line {{incode|LineFixed}} that has to fulfilled the constraint
* {{incode|PointOfLineFixed}} indicates which vertex of {{incode|LineFixed}} has to fulfill the constraint
* {{incode|LineMoving}} is the number of the line, that will move by applying the constraint
* {{incode|LineMoving}} is the number of the line, that will move by applying the constraint
* {{incode|PointOfLineMoving}} is the number of the line {{incode|LineMoving}}, that has to fulfilled the constraint
* {{incode|PointOfLineMoving}} indicates which vertex of {{incode|LineMoving}} has to fulfill the constraint


<!--T:10-->
<!--T:45-->
As the names {{incode|LineFixed}} and {{incode|LineMoving}} indicate, if both constrained vertices are free to move in any direction, the first one (first to be selected in the Gui) will remain fixed and the other one will move. In the presence of existing constraints, however, both edges may move.
The main issue by using this function is to identify correctly the line number and the vertex number of the lines you want to process.


<!--T:11-->
<!--T:46-->
The [[Sketcher_scripting|Sketcher scripting]] page explains the values which can be used for {{incode|LineFixed}}, {{incode|PointOfLineFixed}}, {{incode|LineMoving}} and {{incode|PointOfLineMoving}}, and contains further examples on how to create constraints from Python scripts.
The next paragraph will explain you how to identify the numbering of a line and of a vertex of a line.


===Identifying the numbering of a line=== <!--T:15-->

<!--T:12-->
I have drawn three lines as shown in the following figure.

<!--T:16-->
[[File:PartDesignConstraintPointOnPointScriptingFigure1.jpg|600px]]

<!--T:17-->
By moving the cursor of the mouse above the line you can see the line number at the bottom left of the FreeCAD windows, see next figure.

<!--T:18-->
[[File:PartDesignConstraintPointOnPointScriptingFigure2.jpg|600px]]

<!--T:19-->
Unfortunately the numbering displayed on the FreeCAD windows start from 1 whereas the numbering of the line used to script start from 0: this means that you have to retrieve one each time you want to refer to a line.

===Identifying the numbering of the vertices of a line=== <!--T:20-->

<!--T:21-->
The vertices of one line can only have the value 1 or 2. (Don’t ask me, why the vertices numbering does not start from 0 …) The vertices are numbered according to their order of creation. To find out the order of their creation (If you have a lot of lines, you cannot remember which vertex you have created first), you just have to move the cursor of your mouse above the two vertices of one line, see following figure.

<!--T:22-->
[[File:PartDesignConstraintPointOnPointScriptingFigure3.jpg|600px]]

<!--T:23-->
If you read e.g. 4 and 5, it means that the vertex 4 will be referenced by using the number 1 in the script command and the vertex 5 will be referenced by using the number 2 in the script command. Etc.

=== Example === <!--T:24-->

<!--T:25-->
Let us take the previous example of the three lines. The subsequent figure indicates the numbering of each line and their vertices according to the convention for scripting.

<!--T:26-->
[[Image:PartDesignConstraintPointOnPointScriptingFigure3Bis.jpg|600px]]
{{Caption|<b>blue text:</b> numbering of line, <b>black text:</b> numbering of vertices}}

<!--T:27-->
The command {{incode|Sketch.addConstraint(Sketcher.Constraint('Coincident',1,2,2,1))}} yields following result:

<!--T:29-->
[[Image:PartDesignConstraintPointOnPointScriptingFigure4.jpg|600px|center]]

<!--T:30-->
The command {{incode|Sketch.addConstraint(Sketcher.Constraint('Coincident',0,2,2,2))}} yields following result:

<!--T:38-->
[[Image:PartDesignConstraintPointOnPointScriptingFigure5.jpg|600px|center]]


<!--T:33-->
<!--T:33-->
{{Docnav
{{Docnav
|[[Sketcher_ToggleConstruction|Construction Mode]]
|[[Sketcher_ToggleConstruction|Construction Mode]]
|[[Sketcher ConstrainPointOnObject|Point On Object]]
|[[Sketcher_ConstrainPointOnObject|Point On Object]]
|[[Sketcher_Workbench|Sketcher]]
|[[Sketcher_Workbench|Sketcher]]
|IconL=Sketcher_ToggleConstruction.svg
|IconL=Sketcher_ToggleConstruction.svg
|IconR=Constraint_PointOnObject.svg
|IconC=Workbench_Sketcher.svg
|IconC=Workbench_Sketcher.svg
|IconR=Constraint_PointOnObject.svg
}}
}}



Revision as of 13:00, 24 January 2021

Sketcher ConstrainCoincident

Menu location
Sketch → Sketcher constraints → Constrain coincident
Workbenches
Sketcher
Default shortcut
C
Introduced in version
-
See also
Sketcher Constrain Lock, Sketcher Constrain Point onto Object

Description

Create a coincident constraint on the selected item

This constraint tool takes two points as its argument and serves to make the two points coincident. (Meaning to make them as-one-point).

In practical terms this constraint tool is useful when there is a break in a profile for example - where two lines end near each other and need to be joined - a coincident constraint on their end-points will close the gap.

Usage

As stated above, this tool takes two arguments - both are points.

  1. First, it is necessary to highlight two distinct points. (Note: this will not work if, for example, you attempt to select the start and end point of the same straight line; selecting the start and end points of an arc will produce a closed circle or ellipse but will constrain the location of the seam to be on that point).
  2. Highlighting of a drawing item is achieved by moving the mouse over the item and clicking the left-mouse-button.
  3. It is also possible to highlight all items inside a rectangle by clicking and dragging. When dragging from left to right (with any vertical motion), only the shapes which are entirely contained within the rectangle will be highlighted; in the other direction all shapes which intersect with the selection rectangle will be highlighted. This can be used to select only the vertices without selecting the edges, by dragging a small recangle around some vertices from left to right, as long as there are no edges which are fully contained within the rectangle.
  4. A highlighted item will change its color to green. (This color can be customized in Editing → Preference → Display → Colors → Selection)
  5. Subsequent items can be highlighted by repeating the above procedure(s). Note: it's unnecessary to hold-down any special key like Ctrl to achieve multiple item selection in a drawing.
  6. Once you have two points highlighted, you can invoke the command using several methods:
    • Pressing on the Coinstrain coincident constraint button in the toolbar.
    • Using the C keyboard shortcut.
    • Using the Sketch → Sketcher constraints → Constrain coincident entry in the top menu.

Result: the command will cause the two points to become coincident and be replaced by a single point.

Note: In order to make two points coincident, FreeCAD must out of necessity move one (or both) of the original points.

Alternatives to Coincident constraint

The two constrained items of a Coincident constraint must be start point or end point vertices, or center points of arcs, circles or ellipses. Some combinations which are not possible with a coincident constraint can be emulated using other constraints:

  • The Symmetric constraint can be used to place a start point, end point or center point on the midpoint of a straight line.
  • A midpoint-to-midpoint placement of two straight lines can be achieved by creating a new Point and using two Symmetric constraints so that it lies on the midpoint of both lines.
  • A vertex can be constrained to lie along an edge using a PointOnObject constraint. Note that with this constraint, the point can lie anywhere on the full extension of a segment or curve (i.e. also before the start point or beyond the end point).
  • A collinear placement of two straight lines can be obtained by applying a Tangent constraint to them, or by combining a PointOnObject constraint and a Parallel constraint.
  • Two edges can be made identical by using two Coincident constraints, one for each pair of extremities.
  • Two circles can be made identical by using a Coincident constraint to merge the centers, and applying an Equal constraint to their edges. For arcs, this will ensure both arcs are part of the same circle, while allowing them to have different start and end points.

Scripting

The constraint can be created from macros and from the Python console by using the following command:

Sketch.addConstraint(Sketcher.Constraint('Coincident',LineFixed,PointOfLineFixed,LineMoving,PointOfLineMoving))

where :

  • Sketch is a sketch object
  • LineFixed is the number of the line, that will not move by applying the constraint
  • PointOfLineFixed indicates which vertex of LineFixed has to fulfill the constraint
  • LineMoving is the number of the line, that will move by applying the constraint
  • PointOfLineMoving indicates which vertex of LineMoving has to fulfill the constraint

As the names LineFixed and LineMoving indicate, if both constrained vertices are free to move in any direction, the first one (first to be selected in the Gui) will remain fixed and the other one will move. In the presence of existing constraints, however, both edges may move.

The Sketcher scripting page explains the values which can be used for LineFixed, PointOfLineFixed, LineMoving and PointOfLineMoving, and contains further examples on how to create constraints from Python scripts.