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Facet error after conversion from TCSurface to ACIS Solid
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January 10, 2019, 03:11:22 AM
I needed to make the STL file 1 mm thicker from front to back.

The attached image shows what happened after I did the following:
(I'd have uploaded the TCW file, but it's 25 MB)

1. Imported hi-res STL original.
2. Drew two Arcs above and below the frame and Lofted them so that they created a front and rear boundary.
3. Copied the Loft forward and backward and Lofted each pair together so that the resulting solids overlapped the desired front and rear sections of the frame.
4. After converting Lofts to TCSurfaces, 3D Subtracted them from copies of the frame to make the front and rear sections.
5. Moved the rear section back 1 mm.
6. (Arduously) traced the edges of the front piece (outer frame and two lens holes) using 3D Polyline.
7. Copied the 3D Polyline and moved it back 1 mm.
8. Lofted the each 3D Polyline to its copy to create a 1 mm thick filler.
9. 3D Added the front, rear and filler sections together.
10. Converted to ACIS Solid.
11. Viewed in Dynamic Cut Plane (I should point out that saving as STL from either TCSurface or ACIS Solid and viewing with MeshLab also indicates the same error).

I'm wondering if this is caused by the order in which I select the 3D Polylines for Lofting, in part.

As it turns out, it is.  The direction in which you draw the 3D Polyline around the boundary interacts with the order in which you select the 3D Polyline and its copy for Lofting (steps 6 & 8).

Is there the means of flipping all the facets in a selected Loft?  I doubt it, but there should be.


Jeff

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TC Pro Platinum 2019, 2018, 2017, 2016 & 2015 (all with LightWorks & RedSDK) & V21
System: i7-5820K @ 3.30GHz, ASRock X99 Extreme4, 16GB DDR4-2133 RAM, Gigabyte GTX 970, Samsung NVMe SSD 950 (256GB), Windows 7 Pro (64-bit) SP1


* January 10, 2019, 09:44:43 AM
#1
Could you have cut the frame into two pieces (by extruding a suitable open 2D Spline and then using Slice by Surface), then moving one piece 1mm away from the other, then using Extrude to Face or F2F Lofting to fill the gap?

Henry H

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* January 10, 2019, 01:50:12 PM
#2
Can't you use node edit to displace front or rear faces of the original .stl mesh the 1mm you want?  It ought to do nothing more than alter the aspect ratio of the triangles in the stretch zone.   

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January 10, 2019, 03:01:12 PM
#3
... then using Extrude to Face or F2F Lofting to fill the gap?

Those were my first attempts (after converting to ACIS Solid).  They failed.


Jeff
« Last Edit: January 10, 2019, 03:04:23 PM by Jeffin90620 »

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TC Pro Platinum 2019, 2018, 2017, 2016 & 2015 (all with LightWorks & RedSDK) & V21
System: i7-5820K @ 3.30GHz, ASRock X99 Extreme4, 16GB DDR4-2133 RAM, Gigabyte GTX 970, Samsung NVMe SSD 950 (256GB), Windows 7 Pro (64-bit) SP1


January 10, 2019, 03:14:52 PM
#4
Can't you use node edit to displace front or rear faces of the original .stl mesh the 1mm you want?  It ought to do nothing more than alter the aspect ratio of the triangles in the stretch zone.

The top of the frame is forward of the bottom and the frame is curved in the Z axis.  With the bottom of the lens frame being on the thin side, I just didn't see any way to do that.

BTW: It would be trivially simple for the programmers to add the ability to augment the Extract Loop function so that it works with TC Surface objects by noting which edges are part of only one triangle and building a 3D Polyline.


Jeff

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TC Pro Platinum 2019, 2018, 2017, 2016 & 2015 (all with LightWorks & RedSDK) & V21
System: i7-5820K @ 3.30GHz, ASRock X99 Extreme4, 16GB DDR4-2133 RAM, Gigabyte GTX 970, Samsung NVMe SSD 950 (256GB), Windows 7 Pro (64-bit) SP1


* January 10, 2019, 03:56:47 PM
#5
I don't know the cutoff between trivially simple and not so much, but you can do that by exploding a copy of the mesh down to line segments, deleting all but the edge you want to riff with - it's pretty simple to select them and exclude the edge segments by swinging your viewpoint and selection fence attitude - and then joining the edge segments to a 3D polyline.   

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January 10, 2019, 04:14:10 PM
#6
I don't know the cutoff between trivially simple and not so much, but you can do that by exploding a copy of the mesh down to line segments, deleting all but the edge you want to riff with - it's pretty simple to select them and exclude the edge segments by swinging your viewpoint and selection fence attitude - and then joining the edge segments to a 3D polyline.

I started by joining the edge segments to a 3D Polyline (well, V-snapping a 3D Polyline to the edge segments).  Didn't see the need to select and delete all the other stuff.


Jeff

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TC Pro Platinum 2019, 2018, 2017, 2016 & 2015 (all with LightWorks & RedSDK) & V21
System: i7-5820K @ 3.30GHz, ASRock X99 Extreme4, 16GB DDR4-2133 RAM, Gigabyte GTX 970, Samsung NVMe SSD 950 (256GB), Windows 7 Pro (64-bit) SP1


* January 10, 2019, 04:45:14 PM
#7
That'd be an issue if you were trying to program the edge loop function you described for .stl files, part of that file definition is that edges must be  shared with the edge of one adjacent triangle.

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