topic Re: easier way to flip arc normal in AutoCAD Forum

easier way to flip arc normal

GilesPhillips — Thu, 02 Feb 2023 09:32:33 GMT

It turns out that whilst the exportlayout command is great, its output frequently produces arcs with a normal that is inverted (i.e. normal Z is -1). this makes it impossible to join these arcs into polylines without flipping (though they will join into splines). I currently do this by moving the view into an isometric and using 3d rotate about the x or y axis then reposition if necessary.

This is a bit of a chore. is there a better way of doing it?

I guess if the Autodesk developers team feel like fixing this 'feature' that would be great too 🙂

(Running fully up to date Acad 2023)

Re: easier way to flip arc normal

ВeekeeCZ — Thu, 02 Feb 2023 09:42:02 GMT

Are they flat? If so, you can select them all and use FLATTEN to flip them.

Re: easier way to flip arc normal

GilesPhillips — Thu, 02 Feb 2023 09:46:32 GMT

yep, they're flat and coplanar with all other elements.

I can also successfully join into polylines if I flip the ucs 180deg about the x or y axis. however I'd prefer to avoid this as these files are exported to 3rd party software which may not react favourably to a 'back to front' polyline.

Re: easier way to flip arc normal

ВeekeeCZ — Thu, 02 Feb 2023 10:07:52 GMT

OK, then again, try to use the FLATTEN.

Re: easier way to flip arc normal

GilesPhillips — Thu, 02 Feb 2023 10:10:49 GMT

flatten makes no difference 😞

Re: easier way to flip arc normal

ВeekeeCZ — Thu, 02 Feb 2023 10:13:22 GMT

Well, then I misunderstood how it's flipped. Would you post a dwg sample of one of those?

Re: easier way to flip arc normal

SEANT61 — Thu, 02 Feb 2023 10:27:57 GMT

Mirror3d is pretty easy.

Command: LIST Select objects: 1 found Select objects: ARC Layer: "0" Space: Model space Handle = 1ee center point, X= 10.9360 Y= 4.0019 Z= 0.0000 radius 0.6121 Extrusion direction relative to UCS: X= 0.0000 Y= 0.0000 Z= -1.0000 length 1.6748 total angle 157 Command: MIRROR3D Select objects: 1 found Select objects: Specify first point of mirror plane (3 points) or [Object/Last/Zaxis/View/XY/YZ/ZX/3points] <3points>: xy Specify point on XY plane <0,0,0>: Delete source objects? [Yes/No] <N>: y Command: LIST Select objects: 1 found Select objects: ARC Layer: "0" Space: Model space Handle = 1ee center point, X= 10.9360 Y= 4.0019 Z= 0.0000 radius 0.6121 start angle 309 end angle 106 length 1.6748

Re: easier way to flip arc normal

GilesPhillips — Thu, 02 Feb 2023 10:31:11 GMT

Attached are 2 files. (I've deleted some irrelevant detail)

in the 2d file you'll need to explode the blocks first, then you'l l see each and every arc appears to have its normal flipped. I want to join these segments to adjoining lines to present a series of closed polylines for our fabricators to cut on their CNC cutters. I've had plenty of grumbling in the past about anomalous entities in CAD files upsetting the software, so I try to present them with files as simple as possible with all blocks exploded, closed polylines, etc..

The file is produced from using the exportlayout command on a file (attached, called 3d) with 3d views of autocad native solids.

Re: easier way to flip arc normal

GilesPhillips — Thu, 02 Feb 2023 10:43:03 GMT

ooh, mirror3d, that looks cool will try that for the interim.

bonus points figuring out a way to stop the arcs being inverted in the first place 🙂

Re: easier way to flip arc normal

ВeekeeCZ — Thu, 02 Feb 2023 10:59:56 GMT

Must be missing something. FLATTEN works flawlessly.

I can either select all blocks, flatten, explode. Or Explode, select all arcs, flatten.

Both workflows result in arcs with +1 Z.

Re: easier way to flip arc normal

GilesPhillips — Thu, 02 Feb 2023 10:56:53 GMT

How odd.

I'm going to have to review the differences in the source files again perhaps because it definitely wasn't doing it yesterday..

oh well - many thanks for your input on this.

Re: easier way to flip arc normal

SEANT61 — Thu, 02 Feb 2023 10:57:20 GMT

Indeed, flatten does work here as well.

Leave "Remove hidden lines? <No>:" as no.

Re: easier way to flip arc normal

GilesPhillips — Thu, 02 Feb 2023 11:08:37 GMT

Maybe that was the bit I did wrong..

Re: easier way to flip arc normal

Kent1Cooper — Thu, 02 Feb 2023 12:52:36 GMT

@ВeekeeCZ wrote:

.... FLATTEN works flawlessly. ....

... except that it moves those Arcs that are not a Z=0 in elevation to there. Surely that is not wanted.

Re: easier way to flip arc normal

Kent1Cooper — Thu, 02 Feb 2023 13:19:48 GMT

@GilesPhillips wrote:

.... arcs with a normal that is inverted (i.e. normal Z is -1). .... impossible to join these arcs into polylines without flipping....

How about this? It checks each Arc among the selection for a Z coordinate of its extrusion direction of -1, and if that's the value, it spins it around 180° about the axis from its center to its midpoint, preserving non-zero elevations. [lightly tested]

(vl-load-com) (defun C:ANDU ; = Arc Normal Down to Up (/ ss n arc) (if (setq ss (ssget '((0 . "ARC")))) (repeat (setq n (sslength ss)); then (setq arc (ssname ss (setq n (1- n)))) (if (equal (cadddr (assoc 210 (entget arc))) -1.0 1e-2); downward normal? (command ; then "_.ucs" "_zaxis" "_non" (getpropertyvalue arc "Center") "_non" (vlax-curve-getPointAtDist arc (/ (getpropertyvalue arc "Length") 2)) "_.rotate" arc "" "_non" "0,0" "180" "_.ucs" "_previous" ); command ); if ); repeat ); if (prin1) )

Re: easier way to flip arc normal

RobDraw — Fri, 03 Feb 2023 11:38:48 GMT

@GilesPhillips wrote:
It turns out that whilst the exportlayout command is great, its output frequently produces arcs with a normal that is inverted (i.e. normal Z is -1). this makes it impossible to join these arcs into polylines without flipping (though they will join into splines).

Maybe a different way of exporting will prevent this from happening.

Re: easier way to flip arc normal

GilesPhillips — Fri, 03 Feb 2023 11:45:06 GMT

Possibly, however the exportlayout is a great way of quickly getting flat geometry from occasionally complex 3d geometry that's already been arranged in paperspace using 3d views. Flatshot is okay for 'raw' geometry, but not so much for curated geometry with context. As I'm creating the paperspace layout for other purposes, it makes sense to use exportlayout to generate my 2d stuff.

Re: easier way to flip arc normal

RobDraw — Fri, 03 Feb 2023 12:07:11 GMT

@GilesPhillips wrote:
it makes sense to use exportlayout to generate my 2d stuff.

Until the output is undesirable. Exploring other options may reveal a better solution. Just saying.