Sketchup is Inacurrate???

Wo3Dan

...
Edit: The result needs to be an offset copy of the original arch, with the same parameters, amount of segments, just bigger or smaller depending on the side of the offset......

There are quite a few situations (more than you would like to believe) where this is NOT possible at all when dealing with segmented arcs. Even if you want to take them all along the operation as true arcs. In the end you'll have to present the geometry as segmented.
(Reread my previous post)
Only, and I mean only when dealing with tangent at vertex all along the curve, SU can keep segmented arcs after the offset operation.
I've put two and two together in the next (attatched) file.
Lets say I'm one of the developers and I would like you and Jeff and others to come up with the best solution with how to solve the connection edge-arc-edge in presented situation.
Decide which location (F or G or H) and on the other side (K or L) would be acceptable for you. Whatever you think would be right, SketchUp has to compromise due to dealing with segments. The arc will be chopped off and in best cases you'll end up with an arc part with less segments.

The model on the right represents a curve with arcs (no matter how many sides, they vary).
They are all connected tangent at vertex.
Only in this situation you'll be able to get an offsetted curve consisting of arcs that are true offsets at vertex: they can be changed in number of segments, they are still connected tangent, the 'Follow Me' tool keeps the vertex cross sections predictable, a next offset would be possible, still keeping all arcs as arcs, though again segmented.
Even edges can be part of the curve, provided that they connect perpendicular to the local end radius of arc involved

In all other situations you can't get what you are after with segmented arcs.

Arc offset issues when dealing with segmented arcs

DesertRaven

@jbacus said:

@gilles said:

and also a circle tool wich works like the rotate tool

John, would it be possible to incorporate a "lath / revolve" function in to the existing "protractor tool"?
It would be done by adding an option triggered by holding down the "alt" key to create revolved shapes.

Like copying using the protractor tool, one could choose how many segments one wants to create by either typing in "x" followed by number or "/" followed by number?

Well a "compass tool" that acts like the "tape-measure" tool and creates "dash lined" true circles to find intersections would be very handy.

pilou

No image or V6 file about the Arc_offset_issues?
(think of old pro & free version users)

DesertRaven

@wo3dan said:

@desertraven said:

...
Edit: The result needs to be an offset copy of the original arch, with the same parameters, amount of segments, just bigger or smaller depending on the side of the offset......

There are quite a few situations (more than you would like to believe) where this is NOT possible at all when dealing with segmented arcs. ...... segmented arcs.

Looks like the arch at "A" isn't tangent to the wall? Judging from the pink circle.

DesertRaven

Wo3Dan brought up a valid point, as shown in the below diagram, if the offset curve needs to convert into a polygon, there is a problem.

jeff hammond

@wo3dan said:

Lets say I'm one of the developers and I would like you and Jeff and others to come up with the best solution with how to solve the connection edge-arc-edge in presented situation.

nice gerrit
yeah.. it's a weird one and at this point, i honestly can't see a simple solution to it.. i'll think about it some more and see if something appears..

for now, i think i've drawn the offset correctly in this .skp.. as in, i'm pretty sure this is how it should look.. but it's definitely not a case of "just move the arc vertices inward.. easy"

offset_issue_gerrit.skp

[EDIT]
here's an alternate solution which has the arc vertices in alignment towards the centerpoint then an oddball segment at the end.. (i talk about it some in the next post)

offset_issue_alternate.skp

jeff hammond

@Gerrit

i guess what would have to happen in that situation is that the arc is being viewed as a true arc in it's calculations..

so where ever the straight edge intersects with the true arc is where the new vertex is place..

of course, doing this misaligns the vertices between it and the arc it was offset from but i don't think that matters.. because that's whats going to happen anyway if you draw it manually..

it's a weird shape (a kink between an arc and a straight line..)..

another situation where you'll see this same behavior though even more mind boggling in a polymodeler would be two arcs mitered together.. imagine a V shape with the left and right half being drawn with different radius arcs..
it's going to get weird in there -- even trying to draw it manually.. which is all the more reason to have it automated

[EDIT] another option would be to have all the vertices line up towards the center point except that one last segment would be shorter… but i can see that as being mega odd to implement
fwiw, i do have a dynamic component that does this.. it divides an arc according to it's length (as opposed to segment length) then the last segment is more often than not, shorter than the rest.. but it's still on radius.
mess around with "Rib Spacing" in the component options dialog to see what i'm talking about..

driven

This is what I mean...
if added separately at true intersect point
they come pretty dam close
john

jeff hammond

@gerrit..

fwiw, that thing is nearly impossible to offset manually in sketchup.. good challenge !

jeff hammond

@driven said:

hey Jeff,

can you see any inaccuracy with my effort, it looks better with more sides, but you can still change those...
john

is this the same one you uploaded a little earlier?
that one has lots of errors in there

all the numbers should be 1.5 or 2.5 for the arc radius (which share the same center point) then 1m for the edge offset..
(your edges aren't parallel either)

2Arcs_6sided v6.jpg

jeff hammond

it's not obvious upon opening gerrit's file that it has this weirdness in it.. (ie- took me a while just to figure out why it was acting so weird )

but an exaggerated version looks like this:

driven

@unknownuser said:

...
then 1m for the edge offset..
(your edges aren't parallel either)

neither of these matter for an accurate drawing, it's the radius and the distance from centre point that all other cad systems care about.

boost the number of sides if you just want it to 'look right', but I thought the point was to be as geometrically accurate as possible with the given tools?

john

jeff hammond

@driven said:

neither of these matter for an accurate drawing, it's the radius and the distance from centre point that all other cad systems care about.

boost the number of sides if you just want it to 'look right', but I thought the point was to be as geometrically accurate as possible with the given tools?

john

hmm.. i think in this little segment of the thread, gerrit brought up the issue of dealing with offsetting a series of edge-arc-edge when the edges and arc aren't tangent..
but in this situation, the edges are definitely important.. (it's just that they aren't in the discussion that much because sketchup already offsets them correctly..)

but making sketchup offset arcs properly then edges improperly.. i think that's probably a worse scenario then what's currently going on

Gaieus

@jbacus said:

@gilles said:

and also a circle tool wich works like the rotate tool

I'm not clear what you mean by referencing the Rotate tool. I think you mean you'd like a tool in SketchUp similar to LayOut's Arc tool— with which you set 'center point', 'arc start' then 'arc end'? Is that correct?

john

No, he probably means this: http://sketchucation.com/resources/tutorials/37-beginner/136-aligning-the-rotate-and-protractor-tools#click-drag

I have a feature request filed for this, too.

driven

@unknownuser said:

but making sketchup offset arcs properly then edges improperly.. i think that's probably a worse scenario then what's currently going on

@unknownuser said:

If i agreed with you on that. then we'd both be wrong!

Well, this appears to be the conundrum for the all those who oppose changes (i.e. the other side off this argument), and why I say it needs to to a 'new' tool or an 'option' for those who need accuracy, above aesthetics.

I tried to show it can be achieved natively,
however,
as I said earlier, a tool, exposing the centre point and arc end point as rotatable handles with snapping would make this easier.
john

DesertRaven

If you guy's ever bothered looking at my AutoCAD drawing it would strike you what is really going on and what is needed to create an accurate model.

You can clearly see the real arches that are tangentially connected to the two "walls".
The offset red segment is offset perpendicular which is wrong. if it were offset following the radius it would be correct.

Because a true arch, being completely round without the facets would have the exact offset value of the 2 units.
Tuning them into facets means you cut off the roundness in each segment, which would make the parallel distance across the facet curves smaller. Still in the vertices the distance stays true to the 2 units. Even if you changed the number of facets the edges follow the true curve, the flat distance in the resulting segments changes with the numbers.

Edit: and @ Gerrit, your example is not tangential to both walls. If they were it would be quite clear what is correct. The segmented Arch still needs to act as a real arch not like a polygon. That's why we need a compass tool to display a real circle/ arch then the user can decide what looks better and Sketchup does not need to guess.

driven

@desertraven said:

If you guy's ever bothered looking at my AutoCAD drawing it would strike you what is really going on and what is needed to create an accurate model.

Hi, I did look at your autocad image before doing exactly what your talking about in Sketchup, if you overlay it on Gerrit's you'll see it has the same centre point for two true arcs that end cleanly at the fixed wall thickness.

I think there's a actually a rounding of 0.000695mm, so would be interested to know how autocad sees it.
john

jeff hammond

@driven said:

I tried to show it can be achieved natively,
however,
as I said earlier, a tool, exposing the centre point and arc end point as rotatable handles with snapping would make this easier.
john

see, this could turn into a zillion more pages but it shouldn't.. regardless, the drawing you showed isn't offset properly..

@desertraven said:

If you guy's ever bothered looking at my AutoCAD drawing it would strike you what is really going on and what is needed to create an accurate model.

i tried but i don't understand what you're showing..

@unknownuser said:

You can clearly see the real arches that are tangentially connected to the two "walls".
The offset red segment is offset perpendicular which is wrong. if it were offset following the radius it would be correct.

Edit: and @ Gerrit, your example is not tangential to both walls. If they were it would be quite clear what is correct. The segmented Arch still needs to act as a real arch not like a polygon. That's why we need a compass tool to display a real circle/ arch then the user can decide what looks better and Sketchup does not need to guess.

you might of missed the whole point of gerrit's drawing.. it's supposed to be that way.. he's exposing a situation when arc's aren't tangent to the walls.. so if your autocad drawing has both lines tangent to the arc then it's missing the point..

thing is, one offset tool can handle the situation correctly.. it just has to work differently than my other idea of a fix which was to "always move the vertices inward or outward then connect with straight lines"

there's no need for a separate tool because thatwould be goofy.. you should be able to select the perimeter of a house which has straight lines,arcs, curves, non-tangent arcs, all of it.. select the whole perimeter then offset it accurately in one go.. you don't want to go in there and offset each individual portion on it's own.. thats what you have to do now.. so why introduce a new tool which doesn't solve any problems??

especially, when it's possible to fix the current offset tool to where it works right in all situations.. that is possible ..it's not an "either it works right on arcs" or "it works right on edges" type of deal.. it can work right on both..

Wo3Dan

@DesertRaven,
The example was deliberately not meant to be tangent at both sides. (a practical example, not everything is tangent). You wanted code for a solution in all situations (tangent is easy with SU’s native tools). So my question was for you to come up with what a solution should look like. (equal segments, equal nr as parent , practical and nice looking connection on both ends). I certainly don’t know. I do suspect that it’s impossible with a segmented presentation of true arcs.
@jeff,
Your first solution: arc starts at D and ends at K, equal segments, the endpoints in between have nothing to do with the parent arc. Connection at A-side is weird. the other side looks okay at the expence of….. well, measure endpoint to endpoint, something that was so important to you. Not such a good solution.Your second solution chops off the child arc at side B. At best you’ll have a child arc with one less segment, compared to the parent arc. And now its even a curve. Same weird connection on side A.
@driven (John),
It looks like a clean solution, equal segments and equal number of segments for parent and child arc. Even same point at center. But have you measured across, between corresponding arc segement endpoints? And they do not lign up towards the center. Is this acceptable? Jeff brought up examples where vertex to vertex should be equal to the offset. He wanted limited sides and still maintaining fixed offset. Yours is for “nice looking”, not for having accurate predictable measures across, along the segmented arc.

It looks like there are more than one versions off a new offset tool for arcs and curves. Some need the vertext to vertex to be equal to the offset. Others don’t mind and just go for same point at center and correct radius.
What I’m saying is you can’’t have both at the same time. So then how could this be coded if we cannot even agree on what IS important in the offset?

With multiple arcs (and edges) being connected tangently, this is a whole different matter. You can still offset this “measured vertex to vertex” with SU’s native tools without loosing any information of individual arcs. As long as the offset doesn’t extend any of the radii involved.
This might be a gooud challenge for a plugin. It would speed up offsetting the curve.

jbacus

@gilles said:

No what I we want for circle tool is chose center then pick any inference for axis then chose radius
the same way rotate tool and protractor tool work.

Sorry, but isn't that exactly the way the Circle tool works today?

edit:
@unknownuser said:

No, he probably means this: http://sketchucation.com/resources/tuto ... click-drag

Gotcha- you want to be able to set the working plane without using the inference system.

john
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Sketchup is Inacurrate???

"...exaggerate the essential and leave the obvious unclear." --Vincent Van Gogh