# Sketcher Эллипс по 3 точкам

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Расположение в меню |
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Sketch → Геометрия эскиза → Начертить эллипс по трём точкам |

Верстаки |

Sketcher |

Быстрые клавиши |

отсутствуют |

Представлено в версии |

0.15 |

См. также |

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

## Contents |

## Описание

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.*

## How to use

- Press the
**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

**The tools:**New sketch, Edit sketch, Leave sketch, View sketch, View section, Map sketch to face, Reorient sketch, Validate sketch, Merge sketches, Mirror sketch

**Sketcher geometries:**Point, Line by 2 point,**Create an arc,**Arc, Arc by 3 Point,**Create a circle**, Circle, Circle by 3 Point,**Create a conic**, Ellipse by center, Ellipse by 3 points, Arc of ellipse, Arc of hyperbola, Arc of parabola,**Create a B-spline**, Create B-spline, Create periodic B-pline, Polyline (multiple-point line), Rectangle,**Create regular polygon**, Triangle, Square, Pentagon, Hexagon, Heptagon, Octagon, Create Regular Polygon, Slot, Fillet, Trimming, Extend, External Geometry, CarbonCopy, Construction Mode

**Sketcher constraints****Geometric constraints**Coincident, Point On Object, Vertical, Horizontal, Parallel, Perpendicular, Tangent, Equal Length, Symmetric, Constrain Block**Dimensional constraints**Lock, Horizontal Distance, Vertical Distance, Distance, Radius, Internal Angle, Snell's Law, Internal Alignment, Toggle reference/driving constraint,

**Sketcher tools**Select solver DOFs, Close Shape, Connect Edges, Select Constraints, Select Origin, Select Vertical Axis, Select Horizontal Axis, Select Redundant Constraints, Select Conflicting Constraints, Select Elements Associated with constraints, Show/Hide internal geometry, Symmetry, Clone, Copy, Move, Rectangular Array, 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, Convert Geometry to B-spline, Increase degree, Increase knot multiplicity, Decrease knot multiplicity

**Sketcher virtual space**Switch Virtual Space

User documentation

**Getting started****Installation:**Download, Linux, Windows, MacOS, Docker, AppImage**Basics:**About FreeCAD, Interface, Mouse navigation, Selection methods, Object name, Preferences, Workbenches, Document structure, Properties; Help FreeCAD, Donate

**Help:**Tutorials, Video tutorials**Workbenches:**Std Base; Arch, Draft, FEM, Image, Inspection, Mesh, OpenSCAD, Part, PartDesign, Path, Points, Raytracing, Reverse Engineering, Sketcher, Spreadsheet, Start, Surface workbench, TechDraw, Test Framework, Web**Unmaintained workbenches:**Plot, Robot, Ship**Deprecated workbenches:**Complete, Drawing

**Code:**Addon Manager, Addons, Macros, External workbenches

**Hubs:**User hub, Power users hub, Developer hub