Sketcher CreateEllipseBy3Points

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Revision as of 15:49, 10 February 2024 by FBXL5 (talk | contribs) (some preparation before the final touch)

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

The Sketcher CreateEllipseBy3Points tool creates an ellipse by three points: the endpoints of the major axis (periapsis and apoapsis) and one point on the ellipse outline to define the minor radius. introduced in version 0.22: Or optionally by its center, the end point of the major radius, and the minor radius, see Sketcher CreateEllipseByCenter).

The sequence of clicks is indicated by yellow arrows with numbers.
1 is the periapsis, 2 is the apoapsis, 3 is the point defining the minor diameter,
a is the major diameter, b is the minor diameter (green lines),
c is the ellipse center and f are the focal points.
The blue lines are construction lines for illustration purposes.

Usage

  1. There are several ways to invoke the command:
  2. The cursor changes to a white cross with the command icon.
  3. The Ellipse parameters section (introduced in version 0.22) is added at the top of the Sketcher Dialog.
  4. Optionally press the M key or select from the dropdown list in the parameters section to change the tool Mode:
    • Axis endpoints and radius:
      1. Pick two points to define the major axis. Or with Pos-OVP: enter their X and/or Y coordinates.
      2. Pick a point on outline of the ellipse to define the minor radius. Or with Pos-OVP: enter its X and/or Y coordinates.
    • Center: introduced in version 0.22
      1. Pick the center of the ellipse. Or with Pos-OVP: enter its X and/or Y coordinate.
      2. Pick a point to set the major radius, and the orientation of the major axis. Or with Dim-OVP: enter the major radius of the ellipse and the angle of the major axis.
      3. Pick a point on the outline of the ellipse to define the minor radius. Or with Pos-OVP: enter the minor radius.
  5. The geometry is created and applicable Pos-OVP and Dim-OVP based constraints are added (none for Axis endpoints and radius). A set of internal geometry aligned to it (major diameter, minor diameter, two foci) is also created. The internal geometry can be manually deleted if not needed, and recreated later. See Sketcher Show Hide Internal Geometry.

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.