# Sketcher CreateEllipseBy3Points

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Sketcher CreateEllipseBy3Points |

Menu location |
---|

Sketch → Sketcher geometries → Create ellipse by 3 points |

Workbenches |

Sketcher |

Default shortcut |

G 3 E |

Introduced in version |

0.15 |

See also |

Sketcher Ellipse by center, Sketcher Circle, Sketcher Arc of Ellipse |

## Description

This tool draws an ellipse by picking three points : (1) the periapsis (first crossing of longer diameter with ellipse), (2) the apoapsis (second crossing of longer diameter with ellipse), (3) one point on a side of the longer diameter (a) defining the minor radius (b). (c) is the resulting center and (f) are the focal points.

When starting the tool, the mouse pointer changes to a white cross with a red ellipse icon.

The sequence of clicks is indicated by yellow arrows with numbers. 1 is the periapsis, 2 is the apoapsis, 3 is the defining point for minor diameter, green lines are major and minor diameters. Blue lines are random construction lines just for illustration purpose.

## Usage

- Press the Create ellipse by 3 points button.
- First click in 3D view sets a point that defines the crossing of the major diameter with the ellipse (periapsis). Second click in 3D view sets a point that defines the crossing of the major diameter with the ellipse opposite to the center point (apoapsis). Third click sets a point on the ellipsis defining the minor radius.

- After the third click, the ellipse is created, together with a set of construction geometry aligned to it (major diameter, minor diameter, two foci). The construction geometry can be manually deleted if not needed, and recreated later. See Internal Alignment Constraint and Sketcher Show Hide Internal Geometry.
- Pressing ESC or clicking the right mouse button cancels the function.

## Peculiarities

- Major and minor axes of ellipses are strict and cannot be swapped by resizing the ellipse. This is a consequence of the solver parametrization used (center (x,y), focus1 (x,y) and minor radius length (b)) and the same strict behavior of OpenCascade. The ellipse must be rotated to swap the axes.
- Ellipse can function as a circle when its major and minor diameter lines are deleted, and one of the foci is constrained to coincide with the center. But radius constraint won't work on such a circle.
- Moving the ellipse by edge is the same as moving ellipse's center.

Sketcher

**General:**Create sketch, Edit sketch, Leave sketch, View sketch, View section, Map sketch to face, Reorient sketch, Validate sketch, Merge sketches, Mirror sketch, 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, B-spline, Periodic B-pline, Polyline, Rectangle, Centered rectangle, Rounded rectangle, Triangle, Square, Pentagon, Hexagon, Heptagon, Octagon, Regular polygon, Slot, 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, Diameter, Radiam, Angle, Snell's law, Internal alignment**Constraint tools:**Toggle driving/reference constraint, Activate/deactivate constraint

**Sketcher tools:**Select unconstrained DoF, Close shape, Connect edges, Select associated constraints, Select associated geometry, Select redundant constraints, Select conflicting constraints, Show/hide internal geometry, Select origin, Select vertical axis, Select horizontal axis, Symmetry, Clone, Copy, Move, Rectangular array, Remove axes alignment, Delete all geometry, Delete all constraints

**Sketcher B-spline tools:**Show/hide B-spline degree, Show/hide B-spline control polygon, Show/hide B-spline curvature comb, Show/hide B-spline knot multiplicity, Show/hide B-spline control point weight, Convert geometry to B-spline, Increase B-spline degree, Decrease B-spline degree, Increase knot multiplicity, Decrease knot multiplicity, Insert knot

**Sketcher virtual space:**Switch virtual space

**Additional:**Sketcher Dialog, Preferences, Sketcher scripting

User documentation

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