REAL circles with DXF export?

shirazbj

posted once,but not showed up.

try this:

select the circle
click 'window' and select 'entity info'. A window will pop up.
Change the 'Segments' to a big number.for example from 24 to 360.

The circle will much fine now. Try export DXF now.

Don't know how to tell SketchUp to remember this setting.

TIG

@thomthom said:

Well, SU knows what should be circles.

right - it does know circles (length of arc is accurate and it's not just a sum of the segments)

i'm wondering if something can be done about i problem i encounter sometimes..
seen here:

[attachment=0:tm3mew7z]arc_accuracy.skp[/attachment:tm3mew7z]

does anybody know of a way to do this more accurately? i feel like sketchup knows where the point is that i'm looking for but it doesn't know how to tell me.

thanks for any help

Draw the 8' radius arc.
Select the arc and get its 'entity info', increase the number of segments considerably - for an 8' arc 128 should be more that enough. [You could have entered 128s when making the arc but I'm assuming that your number of segments is usually something like 16, 24 or 32]. The number of segments needed for this 'cut' accuracy goes up 'exponentially' with the radius...
Draw [or move] a long horizontal line at 5' up, so it cuts across the arc.
Where the line crosses the arc will be an approximation of the point you want, its accuracy depends on the number of segments in the arc - the more it has the more accurate the point - unless the circle has 'infinity' segments it will never be exactly right - but we can get it near enough...
Add the horizontal line to the selection (+ctrl) and then use the context-menu (or use a shortcut-key if set), and pick 'Intersect Selected'. This is needed only for v6 work as v7 breaks crossing lines automatically...
The arc will then be split at the line crossing.
Erase the bits of the line and arc you don't need,
Select the remaining arc and 'entity info' it again changing the number of segments back to a more reasonable figure - say 16 or 24... Remember that the number of arc segments multiplies up the faces, edges, shadows etc when you use it with pushpull or followme, so keeping the number modest is usually best...
You now have an arc of the same radius with ends as near to exact as you need, located where you want them - the cut point can never be exact but it will be accurate to within the tolerances you want - only a tiny fraction of an inch out - all because of the temporarily large number of segments used during the cutting operation...
This could be automated in a script...

.

Gjenio

@thomthom said:

Well, SU knows what should be circles. So it's odd that it doesn't write that as circles when exporting to .dwg...

Yesss, I've tought the same!
It's incredible, that shouldn't be so hard to fix...

jeff hammond

yeah TIG, my workflow is basically a version of what you're saying..
i usually draw my arcs with the arc:center&2pts. ruby and i like how it give the option for amount of segments (avoids a trip to the entity info box).. i start off with 96 segments. (and i don't know why 96.. i guess it's just a number i like )

i like your idea about moving a line up to 5' and then intersecting because i always use a construction line instead which means i then have to zoom in and find the actual intersection (which can be difficult when the segments are so close together).

after i have my arc at the right height, i'll right-click/divide it into 8inch segments (8" being my standard on-center layout).. i can then use those vertexes for other calculations i need to do such as:

everything always works out ok in the end but i was hoping something like this would be possible:
[flash=425,344:2uhcs32t]http://www.youtube.com/v/UMvdtFBb4pQ&hl=en&fs=1[/flash:2uhcs32t]

that seems like the easiest/fastest/most accurate method

jeff hammond

i did some experimenting and everything is peachy now

sketchup CAN draw real circles (well, i don't know if other programs will see them as that but that aside, they are true circles)

for some reason, i always thought the maximum amount of segments you could divide an arc into was ~200.. i'm now able to divide them at 10,000+ (confirmed in both statistics and entity info) ... i tested around 10 of my normal sized radii with 2000 segment arcs and they all came up dead accurate (units set to decimal at .0001" precision..

see for yourself.. i draw an 8' arc twice - first with 12 segments then with 2000 segments.. pay attention to the radius lengths in the VCB..

[flash=500,425:2ycai699]http://www.youtube.com/v/VahW0X8ph1A&hl=en&fs=1[/flash:2ycai699]

.

pilou

How have you the Window Box "Arc Parameter"? (is it Mac presentation different than PC?

Matt666

It's Didier's plugin : Arc

@unknownuser said:

Deux nouvelles méthodes de dessin d'arcs: arc passant par trois points, centre et deux points.

pilou

@unknownuser said:

It's Didier's plugin : Arc

This explain that

TIG

Jeff

The detailed breakdown for a 96" radius circle is :-
128 segments >>> +/- 1/32" accuracy.
200 segments >>> +/- 1/64" accuracy.
256 segments >>> ~96" sometimes reported or circumference (the "~" tells us that it's not quite 96" by within 1/128" !).
689+ segments >>> 96" always reported (SketchUp simply gives up - it can't measure it any more accurately).

Considering the degree of accuracy that can be achieved in physically building things in the real world, then a 200 or 256 segment circle (or proportional arc) would seem sufficient for most needs at most day-to-day sizes of things from a few inches to several yards...

I note that your arc had 2000 segments that's equivalent to a 8000 segment circle. Using thousands of edges gives no more benefit and loads the model disproportionately when used to pushpull etc...

pilou

When you say 96" radius circle, is it 243.84 cm circle radius?

TIG

@unknownuser said:

When you say 96" radius circle, is it 243.84 cm circle radius?

Exactly - I used inches for Jeff's sake...
[Exactement - j'ai employé pouces dans l'intéret de Jeff...]
1"=2.54cm
1/32"=0.794mm
1/64"=0.397mm
You can see the accuracy is negligible in 'real-world' terms - when did you ever make a physical model, piece of furniture or a building to such fine tolerances ?
[Vous pouvez voir que l'exactitude est négligeable en termes 'réels' - quand avez-vous jamais fait un maquette, le meuble ou un bâtiment à de telles tolérances fines ?]

...

pilou

Thx for the "precisions"

jeff hammond

yeah TIG, i think i'm being unclear with my intent here.. i'm not too concerned with being 100% precise in order to build accurately (for instance, our tapes are in 1/16" increments so i round to the nearest 16th for the cut lists)..

my concern is the method i previously had to go through in order to draw my arcs.. shown in the first half of this video --

[flash=500,400:ajuoc4zj]http://www.youtube.com/v/sCpbagJfGGQ&hl=en&fs=1[/flash:ajuoc4zj]

it can be a pain to get the point which i achieved at 0:25 in the video.. especially when using a laptop with no mouse as i often do on the jobsite..

you'll see though that i divide my arcs up into 8" segments and there's no way i'm thinking about using a 1000 segment arc for push/pull etc..

i just want to find the point where an 8' radius is 5' tall -- i'm not too concerned with having true circles in SU.. it's just that if they were true, i'd be able to find that point very easily.. by hyper-dividing them into thousands of segments, i can temporarily mimic a true circle and get my construction point..

(and yes, 2000 may be overkill -- that was just an experiment that happened to work out and i didn't try to find the minimum amount i should be dividing them at.. you're saying 689 segments works as well so i'll try something closer to that)