Ticket #4018 - Projecting an ellipse on an inclined plane
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Ticket #4018 - Projecting an ellipse on an inclined plane
I'm working with a model that requires me to constrain to projections of an ellipse to faces in different planes.
I've confirmed with some Googling that the projections are ellipses as well. However, FreeCAD projects these as B-Splines. This is in Sketcher, as external geometry. That's not all that helpful.
I can easily make an ellipse as construction geometry on the Sketcher plane. I have the end points; I just need third point on the original geometry: e.g. the end point of the minor axis would be a good addition. (I may need the center as well, but that problem hasn't come up in my cases yet.)
Question: What is a good way to allow me to get the minor axis end point on my Sketcher plane as external geometry?
The best I can come up with is: break up the original ellipse segments into two segments each. It's just going to be unnecessarily cumbersome all over my parts.
An example demonstrating the issue is attached.
Overall Part: External Geometry as spline: My ellipse construction geometry to work around: I need that third point:
OS: macOS 10.14
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.16117 (Git)
Build type: Release
Branch: (HEAD detached at 0.18.2)
Hash: dbb4cc6415bac848a294f03b80f65e888d531742
Python version: 3.6.7
Qt version: 5.6.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedStates (en_US)
I've confirmed with some Googling that the projections are ellipses as well. However, FreeCAD projects these as B-Splines. This is in Sketcher, as external geometry. That's not all that helpful.
I can easily make an ellipse as construction geometry on the Sketcher plane. I have the end points; I just need third point on the original geometry: e.g. the end point of the minor axis would be a good addition. (I may need the center as well, but that problem hasn't come up in my cases yet.)
Question: What is a good way to allow me to get the minor axis end point on my Sketcher plane as external geometry?
The best I can come up with is: break up the original ellipse segments into two segments each. It's just going to be unnecessarily cumbersome all over my parts.
An example demonstrating the issue is attached.
Overall Part: External Geometry as spline: My ellipse construction geometry to work around: I need that third point:
OS: macOS 10.14
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.16117 (Git)
Build type: Release
Branch: (HEAD detached at 0.18.2)
Hash: dbb4cc6415bac848a294f03b80f65e888d531742
Python version: 3.6.7
Qt version: 5.6.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedStates (en_US)
- Attachments
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- ellipseprojection.FCStd
- (52.56 KiB) Downloaded 41 times
Last edited by Kunda1 on Thu Jun 13, 2019 2:52 pm, edited 1 time in total.
Reason: Updated thread title with bug tracker ticket number
Reason: Updated thread title with bug tracker ticket number
Re: Projecting an ellipse on an inclined plane
Hi
You have to try to find a straight segment to avoid a projection in B-spline
In this case make a cross section "provisional"
You have to try to find a straight segment to avoid a projection in B-spline
In this case make a cross section "provisional"
- Attachments
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- elipse.FCStd
- (48.8 KiB) Downloaded 39 times
-
- elipse.PNG (5.99 KiB) Viewed 1683 times
Last edited by meme2704 on Sat Jun 08, 2019 2:04 pm, edited 1 time in total.
Re: Projecting an ellipse on an inclined plane
Thank you. This sounds promising. Can you elaborate on how?
The "clipping plane" view option is greyed out in Sketcher. The only other related thing I found was "Sketcher->View Section" which is the wrong plane.
Re: Projecting an ellipse on an inclined plane
Use a datumplane and datumpoint with proximity attachment mode between the sketch and edge. Then use the point for external geometry and hook the ellipse on it.
- Attachments
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- aa.FCStd
- (46.38 KiB) Downloaded 43 times
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- Capture2.JPG (22.39 KiB) Viewed 1639 times
Re: Projecting an ellipse on an inclined plane
Thanks. That works beautifully since I know and can define the line along the top of my part.
Of course, I took two steps forward and hit another snag. I wanted to use the same idea for line/plane intersection. The plane is offset from the face a few mm. The Line/Plane proximity point fails with:
Code: Select all
PositionBySupport: AttachEnginePoint::calculateAttachedPlacement: proximity calculation failed.
Re: Projecting an ellipse on an inclined plane
the proximity between datumline and datumplane works.
- Attachments
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- Capture2.JPG (76.14 KiB) Viewed 1576 times
Re: Projecting an ellipse on an inclined plane
Odd. It's never worked for me.
Re: Projecting an ellipse on an inclined plane
If there are no objections, I'll start a bug report on this. It's possible it's a platform-dependent issue (MacOS).
Re: Projecting an ellipse on an inclined plane
I will try to reproduce on the Mac. What are the exact steps?
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Re: Projecting an ellipse on an inclined plane
You can try this file: 1) Create a datum point
2) Select "DatumPlane Offset Incline" as a reference
3) Select "DatumLine Ridge" as a second reference
4) Try "Proximity Point 1" as Attachment mode.
The order of references doesn't matter. Proximity point 2 also does the same.
Alternately, you can start from a new file:
1) Create body
2) Create a Datum Plane (I used detached)
3) Create a Datum Line
4) Create a Datum point and try proximity point as above.