Sketcher ConstrainTangent: Difference between revisions

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{{GuiCommand
{{GuiCommand
|Name=Sketcher ConstrainTangent
|Name=Sketcher ConstrainTangent
|MenuLocation=Sketch → Sketcher constraints → Constrain tangent or collinear
|Workbenches=[[Sketcher Workbench|Sketcher]]
|Workbenches=[[Sketcher_Workbench|Sketcher]]
|MenuLocation=Sketch → Sketcher constraints → Constrain tangent
|Shortcut={{KEY|T}}
|Shortcut={{KEY|T}}
|SeeAlso=[[Sketcher ConstrainPointOnObject|Constraint point on object]]
|SeeAlso=[[Sketcher_ConstrainPointOnObject|Sketcher Constraint point on object]]
}}
}}


==Description== <!--T:29-->
==Description== <!--T:29-->


<!--T:2-->
<!--T:2-->
Tangent Constraint makes two curves to touch each other (be tangent). Lines are treated infinite, and arcs are treated as full circles/ellipses. The constraint is also capable of connecting two curves, forcing them tangent at the joint, thus making the joint smooth.
The [[Image:Sketcher_ConstrainTangent.svg|24px]] [[Sketcher_ConstrainTangent|Sketcher ConstrainTangent]] tool constrains two edges, or an edge and an axis, to be tangent. Lines are treated as infinite, and open curves are virtually extended as well. The constraint can also connect two edges, forcing them to be tangent at the joint. If two lines are selected, or a line and the endpoint of another line, the lines are made collinear.


==Usage== <!--T:30-->
Tangent Constraint can also be used with two lines to make them colinear.


See also: [[Sketcher_Workbench#Drawing_aids|Drawing aids]].
==Usage== <!--T:30-->


===[[Sketcher_Workbench#Continue_modes|Continue mode]]===
<!--T:3-->
There are four different ways the constraint can be applied:
# between two curves (available not for all curves)
# between two endpoints of a curve, making a smooth joint
# between a curve and an endpoint of another curve
# between two curves at user-defined point


# Make sure there is no selection.
<!--T:4-->
# There are several ways to invoke the tool:
To apply tangent constraint, one should the follow the steps:
#* Press the {{Button|[[Image:Sketcher_ConstrainTangent.svg|16px]] [[Sketcher_ConstrainTangent|Constrain tangent or collinear]]}} button.
* Select two or three entities in the sketch.
#* Select the {{MenuCommand|Sketch → Sketcher constraints → [[Image:Sketcher_ConstrainTangent.svg|16px]] Constrain tangent or collinear}} option from the menu.
* Invoke the constraint by clicking its icon on the toolbar, or selecting the menu item, or using keyboard shortcut.
#* {{Version|0.22}}: Right-click in the [[3D_view|3D view]] and select the {{MenuCommand|Constrain → [[Image:Sketcher_ConstrainTangent.svg|16px]] Constrain tangent or collinear}} option from the context menu.
#* Use the keyboard shortcut: {{KEY|T}}.
# The cursor changes to a white cross with the tool icon.
# Do one of the following:
#* Select two edges. The edges can be any edge except a B-spline.
#* Select a point and two edges (in that order).
#* Select an edge, a point and another edge (idem).
# A Tangent constraint is added. If a point and two edges have been selected, up to two [[Sketcher_ConstrainPointOnObject|Point onto object constraints]] can also be added. See [[#Between_two_edges_at_point|Examples]].
# Optionally keep creating constraints.
# To finish, right-click or press {{KEY|Esc}}, or start another geometry or constraint creation tool.


===Run-once mode===
===Between two curves (direct tangency)=== <!--T:5-->
[[Image:Sketcher ConsraintTangent mode1.png|600px]]


# Do one of the following:
<!--T:6-->
#* Select two edges (see above).
Two curves will be made tangent, and the point of tangency will be implicit. This mode is applied if two curves were selected.
#* Select two endpoints belonging to different edges.
#* Select an edge and the endpoint of another edge (in any order).
#* Select a point and two edges (idem).
# Invoke the tool as explained above, or with the following additional option:
#* {{Version|0.22}}: Right-click in the [[3D_view|3D view]] and select the {{MenuCommand|[[Image:Sketcher_ConstrainTangent.svg|16px]] Constrain tangent or collinear}} option from the context menu.
# A Tangent constraint is added. If a point and two edges have been selected, up to two [[Sketcher_ConstrainPointOnObject|Point onto object constraints]] can also be added. See [[#Between_two_edges_at_point|Examples]].


==Examples==
<!--T:7-->

'''Accepted selection:'''
===Between two edges=== <!--T:5-->
* line + line, circle, arc, ellipse, arc-of-ellipse

* circle, arc + circle, arc
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If direct tangency between selected curves is not supported (e.g. between a circle and an ellipse), a helper point will be added to sketch automatically, and tangency-via-point will be applied.
[[Image:Sketcher_ConsraintTangent_mode1.png|400px]]
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The two edges are made tangent. If one of the edges is a [[Sketcher_Workbench#Sketcher_CompCreateConic|conic]], a [[Sketcher_CreatePoint|Point object]] that has a [[Sketcher_ConstrainPointOnObject|Point onto object constraint]] with both (extended) edges is added.


<!--T:8-->
<!--T:8-->
It is not recommended to reconstruct the point of tangency by creating a point and constraining it to lie on both curves. It will work, but the convergence will be seriously slower, jumpier, and will require about twice as many iterations to converge than normal. Use other modes of this constraint if the point of tangency is needed.
It is not recommended to reconstruct the point of tangency by manually creating a point and constraining it to lie on both curves. It will work, but the convergence will be seriously slower, jumpier, and will require about twice as many iterations to converge than normal. If the point of tangency is needed, select two edges and an existing point instead.


===Between two endpoints (point-to-point tangency)=== <!--T:9-->
===Between two endpoints=== <!--T:9-->
[[Image:Sketcher ConsraintTangent mode2.png|600px]]


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<!--T:10-->
[[Image:Sketcher_ConsraintTangent_mode2.png|400px]]
In this mode, the endpoints are made coincident, and the joint is made tangent (C1-smooth, or "sharp", depending on the placement of curves before the constraint is applied). This mode is applied when two endpoints of two curves were selected.
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The endpoints are made coincident, and the angle between the edges at that point is set to 180° (smooth joint) or 0° (sharp joint), depending on the placement of the edges before the constraint is applied.
<!--T:11-->
'''Accepted selection:'''
* endpoint of line/arc/arc-of-ellipse + endpoint of line/arc/arc-of-ellipse (i.e., two endpoints of any two curves)


===Between curve and endpoint (point-to-curve tangency)=== <!--T:12-->
===Between edge and endpoint=== <!--T:12-->

[[Image:Sketcher ConsraintTangent mode3.png|600px]]
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[[Image:Sketcher_ConsraintTangent_mode3.png|400px]]
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<!--T:13-->
<!--T:13-->
In this mode, an endpoint of one curve is constrained to lie on the other curve, and the curves are forced tangent at the point. This mode is applied when a curve and an endpoint of another curve were selected.
The endpoint of one edge is constrained to lie on the other edge, and the edges are made tangent at that point.


<!--T:14-->
===Between two edges at point=== <!--T:15-->
'''Accepted selection:'''
* line, circle, arc, ellipse, arc-of-ellipse + endpoint of line/arc/arc-of-ellipse (i.e., any curve + endpoint of any curve)


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[[Image:Sketcher_ConsraintTangent_mode4.png|400px]]
===Between two curves at point (tangent-via-point) (v0.15)=== <!--T:15-->
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[[Image:Sketcher ConsraintTangent mode4.png|600px]]


<!--T:16-->
<!--T:16-->
The two edges are made tangent at a given point. The point can be any point, e.g. the center of a circle, the endpoint of an edge, or the origin, it can belong to one of the edges, and it can also be a [[Sketcher_CreatePoint|Point object]]. If required [[Sketcher_ConstrainPointOnObject|Point onto object constraint(s)]] are added to ensure the point lies on both (extended) edges. These additional constraints are called [[Sketcher_helper_constraint|helper constraints]].
In this mode, two curves are made tangent, and the point of tangency is tracked. This mode is applied when two curves and a point were selected.


<!--T:17-->
<!--T:19-->
Compared to direct tangency, this constraint is slower, because there are more degrees of freedom involved, but if the point of tangency is needed, it is recommended because it offers better convergence.
'''Accepted selection:'''
* any line/curve + any line/curve + any point
"Any point" can be a lone point, or a point of something, e.g. a center of a circle, an endpoint of an arc, or the origin.


<!--T:18-->
===Between two lines=== <!--T:32-->
For the constraint to work correctly, the point must be on both curves. So, as the constraint is invoked, the point will be automatically constrained onto both curves ([[Sketcher helper constraint|helper constraints]] will be added, if necessary), and the curves will be forced tangent at the point. These [[Sketcher helper constraint|helper constraints]] are plain regular constraints. They can be added manually, or deleted.


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<!--T:19-->
[[Image:Sketcher_ConstraintTangent_mode5.png|400px]]
Compared to direct tangency, this constraint is slower, because there are more degrees of freedom involved, but if the point of tangency is needed, it is the recommended mode because it offers better convergence compared to direct tangency + point on two curves.
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The two lines are made collinear.
<!--T:20-->
The placement of the point before the constraint is applied is a hint for the solver for where the tangency should be. With this constraint, one can constrain two ellipses to touch each other in two places.


==Scripting== <!--T:21-->
==Scripting== <!--T:21-->


<!--T:22-->
<!--T:22-->
Tangent Constraint can be created from [[macros]] and from the python console by using the following:
Tangent Constraint can be created from [[Macros|macros]] and from the [[Python|Python]] console by using the following:
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{{Code|code=
{{Code|code=
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:* {{incode|pointpos1}}, {{incode|pointpos2}} should be 1 for start point and 2 for end point.
:* {{incode|pointpos1}}, {{incode|pointpos2}} should be 1 for start point and 2 for end point.
:* {{incode|geoidpoint}} and {{incode|pointpos}} in {{incode|TangentViaPoint}} are the indexes specifying the point of tangency.
:* {{incode|geoidpoint}} and {{incode|pointpos}} in {{incode|TangentViaPoint}} are the indexes specifying the point of tangency.

<!--T:35-->
The [[Sketcher_scripting|Sketcher scripting]] page explains the values which can be used for {{incode|incurve1}}, {{incode|incurve2}}, {{incode|pointpos1}}, {{incode|pointpos2}}, {{incode|geoidpoint}} and {{incode|pointpos}} and contains further examples on how to create constraints from Python scripts.



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Latest revision as of 17:38, 25 March 2024

This documentation is a work in progress. Please don't mark it as translatable since it will change in the next hours and days.

Sketcher ConstrainTangent

Menu location
Sketch → Sketcher constraints → Constrain tangent or collinear
Workbenches
Sketcher
Default shortcut
T
Introduced in version
-
See also
Sketcher Constraint point on object

Description

The Sketcher ConstrainTangent tool constrains two edges, or an edge and an axis, to be tangent. Lines are treated as infinite, and open curves are virtually extended as well. The constraint can also connect two edges, forcing them to be tangent at the joint. If two lines are selected, or a line and the endpoint of another line, the lines are made collinear.

Usage

See also: Drawing aids.

Continue mode

  1. Make sure there is no selection.
  2. There are several ways to invoke the tool:
    • Press the Constrain tangent or collinear button.
    • Select the Sketch → Sketcher constraints → Constrain tangent or collinear option from the menu.
    • introduced in version 0.22: Right-click in the 3D view and select the Constrain → Constrain tangent or collinear option from the context menu.
    • Use the keyboard shortcut: T.
  3. The cursor changes to a white cross with the tool icon.
  4. Do one of the following:
    • Select two edges. The edges can be any edge except a B-spline.
    • Select a point and two edges (in that order).
    • Select an edge, a point and another edge (idem).
  5. A Tangent constraint is added. If a point and two edges have been selected, up to two Point onto object constraints can also be added. See Examples.
  6. Optionally keep creating constraints.
  7. To finish, right-click or press Esc, or start another geometry or constraint creation tool.

Run-once mode

  1. Do one of the following:
    • Select two edges (see above).
    • Select two endpoints belonging to different edges.
    • Select an edge and the endpoint of another edge (in any order).
    • Select a point and two edges (idem).
  2. Invoke the tool as explained above, or with the following additional option:
  3. A Tangent constraint is added. If a point and two edges have been selected, up to two Point onto object constraints can also be added. See Examples.

Examples

Between two edges

The two edges are made tangent. If one of the edges is a conic, a Point object that has a Point onto object constraint with both (extended) edges is added.

It is not recommended to reconstruct the point of tangency by manually creating a point and constraining it to lie on both curves. It will work, but the convergence will be seriously slower, jumpier, and will require about twice as many iterations to converge than normal. If the point of tangency is needed, select two edges and an existing point instead.

Between two endpoints

The endpoints are made coincident, and the angle between the edges at that point is set to 180° (smooth joint) or 0° (sharp joint), depending on the placement of the edges before the constraint is applied.

Between edge and endpoint

The endpoint of one edge is constrained to lie on the other edge, and the edges are made tangent at that point.

Between two edges at point

The two edges are made tangent at a given point. The point can be any point, e.g. the center of a circle, the endpoint of an edge, or the origin, it can belong to one of the edges, and it can also be a Point object. If required Point onto object constraint(s) are added to ensure the point lies on both (extended) edges. These additional constraints are called helper constraints.

Compared to direct tangency, this constraint is slower, because there are more degrees of freedom involved, but if the point of tangency is needed, it is recommended because it offers better convergence.

Between two lines

The two lines are made collinear.

Scripting

Tangent Constraint can be created from macros and from the Python console by using the following:

# direct tangency
Sketch.addConstraint(Sketcher.Constraint('Tangent',icurve1,icurve2))

# point-to-point tangency
Sketch.addConstraint(Sketcher.Constraint('Tangent',icurve1,pointpos1,icurve2,pointpos2))

# point-to-curve tangency
Sketch.addConstraint(Sketcher.Constraint('Tangent',icurve1,pointpos1,icurve2))

# tangent-via-point (plain constraint, helpers are not added automatically)
Sketch.addConstraint(Sketcher.Constraint('TangentViaPoint',icurve1,icurve2,geoidpoint,pointpos))

where:

  • Sketch is a sketch object
  • icurve1, icurve2 are two integers identifying the curves to be made tangent. The integers are indexes in the sketch (the value, returned by Sketch.addGeometry).
  • pointpos1, pointpos2 should be 1 for start point and 2 for end point.
  • geoidpoint and pointpos in TangentViaPoint are the indexes specifying the point of tangency.

The Sketcher scripting page explains the values which can be used for incurve1, incurve2, pointpos1, pointpos2, geoidpoint and pointpos and contains further examples on how to create constraints from Python scripts.