Intersect Faces issue (please help ASAP)

grizzler · 9 Oct 2013, 10:18

I can't believe that I'm actually having to ask this, but I'm in a real pickle here as I can't get a 3D curved object to intersect with a plane! I've grouped, exploded, intersected the 3D object, intersected the plane. I've attached an xray view which shows the line around the 3D shape where the intersect appears to have taken place, but when I select the plane it also selects the segment within the 3D shape.

You're looking down on a ground floor ceiling that I have just begun and the shape is a cut out in the ceiling allowing light in from the 1st floor glass roof, so now you know why it's important that I sort this out

This is stuff I've done a millions times before and I don't know why it won't work.

Dave R · 9 Oct 2013, 10:20

Can you post the SKP file for the curved piece and the face you want it to intersect?

cotty · 9 Oct 2013, 10:25

You should not explode the object before the intersection.

TIG · 9 Oct 2013, 10:30

The 'Intersect' tool is limited by SketchUp inbuilt tolerances, so if the curved surface is very very faceted, and it could result in new edges <~1mm, then some might be missed out... [your screen-grab did not have hidden-geometry 'on']

The intersection geometry appears in the current context, so if you are editing an object when you do the intersect the cut lines appear in that context...

grizzler · 9 Oct 2013, 10:37

@cotty said:

You should not explode the object before the intersection.

I tried it before exploding and after exploding (basically every possible combination of grouping, one item grouped, all exploded etc)

The thing is though, you can see the outline part way up the 3D shape where the intersect must have occurred, but the face/plane remains unaffected.

I'm in a mega rush with this job as I've been given it at extremely short notice, so I've botched a fix by manually tracing round the 3D shape, which has worked.

Dave R, I'm afraid I've saved the botched version now so I don't have the faulty one to upload to satisfy your curiosity thanks for the offer though.

grizzler · 9 Oct 2013, 10:39

@tig said:

The 'Intersect' tool is limited by SketchUp inbuilt tolerances, so if the curved surface is very very faceted, and it could result in new edges <~1mm, then some might be missed out... [your screen-grab did not have hidden-geometry 'on']

The intersection geometry appears in the current context, so if you are editing an object when you do the intersect the cut lines appear in that context...

I did alter the number of facets from 12 to 48 for the curve, so maybe that's it, but 48 doesn't seem too much of a request for something that size... or does it?

TIG · 9 Oct 2013, 10:47

Intersection limitations usually depends on the the overall size of the objects.
But we can only guess from your screen-grab.
As a simple rule don't try to intersect objects which would result in new edges <~1mm - small surfaces that are very faceted can have facets that are very 'thin', another risk is an object with triangulated facets that are intersected very near to a pointed corner, which can have similar resultant tiny geometry...

grizzler · 9 Oct 2013, 10:49

Thank you chaps.