section plane drawing issue

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uwestoehr
Posts: 1425
Joined: Sun Jan 27, 2019 3:21 am

section plane drawing issue

Post by uwestoehr » Sun Mar 29, 2020 4:16 pm

I noticed that under some circumstances the drawing of section planes fail.

- Take this example document:
ttt.FCStd
testfile
(26.55 KiB) Downloaded 5 times
- open the section view and change its z-position to +3 and Apply
- increase the z-step in steps of one and apply

result: if you go beyond 3 you get strange results, like this one for z = 7:
ttt.FCStd
testfile
(26.55 KiB) Downloaded 5 times

Since the cut section is a plane I don't understand the result and think this is a bug.
Attachments
FreeCAD_wr5goNblla.png
z=7
FreeCAD_wr5goNblla.png (8.15 KiB) Viewed 140 times
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wandererfan
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Joined: Tue Nov 06, 2012 5:42 pm

Re: section plane drawing issue

Post by wandererfan » Sun Mar 29, 2020 7:09 pm

uwestoehr wrote:
Sun Mar 29, 2020 4:16 pm
I noticed that under some circumstances the drawing of section planes fail.
Your section origin (red) is far outside the Cube. The cutting tool (pale blue) doesn't intersect the shape properly.
Attachments
ttt.png
ttt.png (10.43 KiB) Viewed 123 times
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uwestoehr
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Re: section plane drawing issue

Post by uwestoehr » Sun Mar 29, 2020 8:23 pm

wandererfan wrote:
Sun Mar 29, 2020 7:09 pm
Your section origin (red) is far outside the Cube. The cutting tool (pale blue) doesn't intersect the shape properly.
But this is what I mean: the blue plane in your image has an end while a plane is basically endless. It seems I misunderstood the concept. I thought a section is placed in the space (like a datum plane in PartDesign) and the area intersecting it, is drawn as section cut plane.

If it is correct, that we don't have a real plane, where can I set the plane size?
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wandererfan
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Re: section plane drawing issue

Post by wandererfan » Sun Mar 29, 2020 11:38 pm

uwestoehr wrote:
Sun Mar 29, 2020 8:23 pm
But this is what I mean: the blue plane in your image has an end while a plane is basically endless. It seems I misunderstood the concept. I thought a section is placed in the space (like a datum plane in PartDesign) and the area intersecting it, is drawn as section cut plane.
The blue bit gets extruded into a prism which cuts the base shape. I don't know if you can do a boolean cut with a half space. Will have to look at the OCC docs.

IIRC the "plane" is 2x the diagonal of the bounding box of the base figure, centred on the section origin. So if the section origin is within the box of the base figure it should work fine.
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