Sketchup is Inacurrate???

[Jeff Hammond]

ok.. here's one more attempt at showing this problem…


in the attached .skp, i will be drawing a U shaped tube.

utube.skp

utube.jpg

i think it's highly important to understand scene 3 in this .skp… if you can realize that scene 3 is proper/accurate, then you will be able to see the inaccuracies in sketchup..


[this file also attempts to show how and are closely related.. scene8 discusses that]





[edit]
oh.. here's the same drawing in su6 for pilou

utube_su6.skp

[Pilou]

The beauty of the V6 is that anybody can reload it! (v6v7v8)

The Follow Me and Keep gives the same result!

[Jeff Hammond]

The beauty of the V6 is that anybody can reload it! (v6v7v8)

The Follow Me and Keep gives the same result!

most of the plugins do unless they are specifically designed to work properly.

shapebender shows the error. roundCorner avoids the error..

try putting a round edge on a cube using followme.. then do the same thing with roundCorner.
see the difference?

[edit]-- i should add however that roundCorner only 'fixes' this issue in one circumstance.. in others, it will still give the same error as followme..

[david.]

Re: the utube, that definitely looks like a problem. It seems the Follow Me version used a different (incorrect) arc radius of 10.0215cm and that arc center point is offset by 0.6554cm from the correct center point. In certain applications, that could be a serious issue. IMO, this should be submitted to Google as a bug.

[Jeff Hammond]

Re: the utube, that definitely looks like a problem. It seems the Follow Me version used a different (incorrect) arc radius of 10.0215cm and that arc center point is offset by 0.6554cm from the correct center point. In certain applications, that could be a serious issue. IMO, this should be submitted to Google as a bug.

hi david.. it's not a bug per se.. there are basically 2 ways to draw/build that pipe… one is by bending (in which case you would use an arc for the followme path… the other way to build it would be to take one length of straight pipe then miter cut it into a bunch of individual pieces then weld them together.. like this:

pipebuild.jpg

and sketchup has accurately depicted this scenario in the .skp i posted..

the problem is that my model used an arc in the path as opposed to straight lines, in which case, the results would be different..

but regardless of my input being an arc or straight lines, sketchup treats both of them the same… it ignores the fact that i have an arc..

[Jeff Hammond]

oh.. and i think i should reiterate what my original post(s) in this thread were meant to say..

you can accurately draw this shape, as a bend, in sketchup..

in the utube case, i'd push/pull the straight sections to 20cm then use TIG's lathe.rb, anchored at the cpoint shown in the .skp to form the semi-circle.. the lathe plugin set to 180º and 12 segments would leave me with geometry that exactly matches the profile array in scene3..

my main point is this: do not use offset or followme on arcs/circles/curves and expect accurate results.. if accuracy is important, use other methods to obtain the precision you require..

if all you need to do is draw a representation of said object and accuracy isn't important, feel free to use offset and followme.. they are generally the fastest way to go about it..

[david.]

hi david.. it's not a bug per se..

Yes, you are correct. It can't be said to be a bug with any certainty. However, the algorithm being used seems to do something other than what I would expect in this case.

[Jeff Hammond]

hi david.. it's not a bug per se..

Yes, you are correct. It can't be said to be a bug with any certainty. However, the algorithm being used seems to do something other than what I would expect in this case.

even then, the algorithm is working just fine (for offsetting shapes which consist of straight edges..).. but now that some people are starting to see this offset error, the topic can maybe shift to why the error occurs and realize how simple it is to fix it..

the process of offsetting isn't difficult at all and it's just simple movement of geometry.. this is why i said earlier that i feel this issue is totally fixable in sketchup.. it's not as if offsetting requires some sort of complex mathematical equation which is failing in certain circumstances.. the problem or inaccuracies occur because of a human choice to ignore 'arcs'.. (ie- it's not that there's a 'bad' algorithm for offsetting.. the problem is that there's no algorithm to begin with for dealing with arcs)

here are a couple of pictures that attempt to illustrate what exactly is happening when offsetting.. the first picture shows how sketchup offsets in all situations.. the second shows how sketchup should offset in the case of an arc..

offsetMiter.jpg

The next picture shows what sketchup should (and could) do if it recognizes an arc as part of the path…

offsetarc.jpg

if it's a line, move the line… if it's an arc, move the vertices


if a user wants to offset in a manner of the first image and they have an arc in the path, they simply explode the arc prior to offsetting..
[ in the same way you would have to explode a 'triangle' created with the so called polygon tool prior to doing anything with it.. a triangle created with the polygon tool is actually a circle being represented by 3 points on the circumference.. entity info of this 'triangle' returns a circle's circumference as opposed to the length of the three sides.. push/pulling this 'triangle' results in softened edges etc.. it's a circle - not a triangle.. if you want to use it as a triangle then you have to explode it first.. (but i guess this is for a different thread )

[Jeff Hammond]

oh.. with the utube example, scene8 was an attempt at making people realize the connection between the offset tool and follow me..
i don't think i nailed it with that example but the following file should, without a doubt, make people see how these two tools are so closely related that it doesn't matter if we speak about them interchangeably.. (i know i keep flip flopping between offset and follow me in my examples.. i just want people to understand that talking about one of these tools applies directly to the other.. it doesn't matter which tool we're talking about.. they work exactly the same and they both ignore arcs..

Offset_and_followme_are_the_same_thing.skp

.

[Pilou]

You forget me

[Rich O Brien]

Here you go Frenchy....

http://sketchup.google.com/intl/en/download/

Join our club

[Jeff Hammond]

You forget me

oops.. changed the file in the post to v6
.

[Pilou]

Thx
On a same plan
A funny thing : you can't offset one segment
You can Offset 2 segments not welded but touching them
You can't Offset 2 separated sets of 2 segments not merged but touching them

@Rich : not on this too old computer

[Jeff Hammond]

Thx

A funny thing : you can't offset one segment
You can Offset 2 segments not welded but touching them
You can't Offset 2 separated sets of 2 segments not merged but touching them

@Rich : not on this too old computer

right, but it makes total sense in sketchup.
it simply has no way of knowing which direction you want to offset if there's only a single line. with more than one line, you've defined a plane so sketchup now knows which direction to go.

[Pilou]

So maybe Radial lines or Radial Lines Fixed Length by Tig can help

here only Font faces were selected! (Snap is automatic ! )

select a CPoint + something then call the plug
Sand Box from scratch for draw lines extremities + some CleanUp/erase
And finally normal Offset for straight lines

radial.jpg

Projections by Didier Bur or Thomthom Guides Tools for Put CPoints at some positions

And if you have exploded some arcs : Explode arcs centerpoint finder by Chris Fullmer

[ely862me]

I'm working at the moment on some very small components and...yes sketchup is not accurate. When I draw some lines, sketchup grabs the lines from different lines,changes lengths,creates some other lines, hides lines.. as it's no able to work with small faces.


Beside that, orbiting or zooming in in small components it's a pain- the clipping/ disappearing objects issue makes i even harder .

[DesertRaven]

Off-Topic:
@jeff hammond EdIT -- the thread was bumped at this point.. conversation is now 9 months later than eli's post

The offset tool is not just a wee tad off, it is way off! And I see no reason why it should not be just fixed. Even if I use this as a conceptual tool only, there are underlying errors that one does not catch right away, only way down the road. I say the programming of the core of sketchup is just straight out sloppy and does, in many cases, not follow geometrical accuracy.
These issues should be honestly sought out, admitted and disclosed to anyone who considers using it to make a living.
By playing these errors down or ignoring them nobody is helped. What it boils down to is deception and who want's that? (the easy to use design tool, but some things don't count on)
Why is it so hard to admit these issues, which indisputably exist and try and work to fix them?
The units are precise enough just the execution of some commands lack performance; why? I just don't get the whole discussion there is no two ways! A command either performs geometrical correct or it does not. If it does not why not fix it?

[Sonder]

Huh? Never had issues with the offset tool. It's always been accurate for me, and I use it all the time.

Clipping occurs if you are far from the origin and set your field of view too wide.

[TIG]

Some clear examples of Offset's inaccuracy please...
You shouldn't make sweeping statements about something like this without some backup

You type in a value or snap to something that is a known distance off, like a guideline...
It is that distance offset.
If you are later measuring offsets on 'arcs' remember that they are 'segmented' and you must measure 'square' to these lines, not from their vertices which will not provide the true offset as this is the 'miter diagonal'...
That is the only source of measurement confusion I can think of... but then that is mis-measurement... and not the application's inaccuracy ?

Which as far as I know is fine for most expected uses...
It's not for designing the innards of swiss-watches or whole city-suburbs but at normal 'building' dimensions it's just fine

[DesertRaven]

:? Some clear examples of Offset's inaccuracy please...
You shouldn't make sweeping statements about something like this without some backup

You type in a value or snap to something that is a known distance off, like a guideline...
It is that distance offset.
If you are later measuring offsets on 'arcs' remember that they are 'segmented' and you must measure 'square' to these lines, not from their vertices which will not provide the true offset as this is the 'miter diagonal'...
That is the only source of measurement confusion I can think of... but then that is mis-measurement... and not the application's inaccuracy ?

Which as far as I know is fine for most expected uses...
It's not for designing the innards of swiss-watches or whole city-suburbs but at normal 'building' dimensions it's just fine

Well let us just pretend you never encountered what I'm talking about so here is an example:

[Jeff Hammond]

These issues should be honestly sought out, admitted and disclosed to anyone who considers using it to make a living.
By playing these errors down or ignoring them nobody is helped. What it boils down to is deception and who want's that? (the easy to use design tool, but some things don't count on)

hey.. i tried back on pg 9

oh, hey..can we get a sketchup rep in the thread ?

[Jeff Hammond]

Huh? Never had issues with the offset tool.

:? Some clear examples of Offset's inaccuracy please...

i'm seriously going to try to avoid getting into this again because last time around (this exact thread) i think i might of pissed off gerritt and that sucks.. he's one of my faves around these parts..

@TIG.. i've discussed this quite a few times with you (latest being in your smartoffset thread)
i seriously thought by now you recognized this error in sketchup but this post is saying otherwise..

this thread contains pretty much all i have to say on the issue.. maybe i'm not as clear as i could be (please let me blame my florida education for lack of communication skills ).. but please read through the thread / look at the .skps again.. maybe go into it with an open or fresh mindset just to humor me..


but Olav is absolutely correct.. the offset tool does not properly deal with arcs..

[Jeff Hammond]

[preemptive]


and before rich calls me a gob o' shite again over this, i would like to say that i fully understand these are first world problems.. i'm just being nerdy about it but in the actual big picture.. i don't care.. at all


[no video.. audio only.... nsfw- language.. maybe a hundred fbombs..]

Video from : www.youtube.com

[/preemptive]

[DesertRaven]

Huh? Never had issues with the offset tool.

:? Some clear examples of Offset's inaccuracy please...

i'm seriously going to try ...


but Olav is absolutely correct.. the offset tool does not properly deal with arcs..

Actually it is worse then only arcs, and to make it clear I am not posting this because I'm trying to bad mouth anyone or Sketchup as such, I am trying to bring some serious issues to light, that seem to just been brushed off with the lamest ever argumentation for too long.

@ TIG, I understand where you are coming from and I have seen much of your great work and effort to make this tool into something useful.
Please try and see my criticism out of the perspective of a every day user who usually never has the time to even go on this forum to discuss any issues they encounter in their every day work life.
I have looked at some of your plug ins and know that you do things different as it is done in sketchup using the native tools available. and I also know you and many others do a great effort to improve this software where it lacks functionality. You write plug ins to make it work or else if all was just good enough you would not even have a reason to do anything. Right?

So please Bear with me for the time being and I will provide more issues and examples where I see the need for improvements. And again I'm NOT asking for more plug ins scripts or more buttons to clutter up the interface.

I am also fed up with work- arounds where there hasn't been a fix for years.
I believe Sketchup can with it's simplicity stand up to any high priced CAD program out there if the core functionality was there. I have worked for years with Sketchup in a fast paced environment and have delivered my part accurate and to satisfaction for my customers. I have done so much research and I have been reading endless hours in this forum on how to work around issues that just occur.

I have lost many hours of my life working with sketchup, but have also saved many hours not working with other more complex software.
To me it is just crazy to see the potential and and for years only read lame excuses why nothing can ever get to the better; why known issues never get fixed. For years on end the only thing I hear is there is a work around... Oh it would not be sketchup any more ... and so on. The worst response I ever read here is "why would you want a cluttered up interface"

I actually think the Interface the simplicity is key to ketchup, I think many others have already learned and implemented simpler interfaces to their complex software. I would not complain about anything if the core of Sketchup would just work (accurate and satisfactory) if issues that are being brought up had been taken serious and fixed.

I'll post some more, to me, obvious fails of Sketchup in this thread and I'm sure a thorough job on the programming side can solve these unnecessary issues.

[thomthom]

and before rich calls me a gob o' shite again over this, i would like to say that i fully understand these are first world problems.. i'm just being nerdy about it but in the actual big picture.. i don't care.. at all

Do care about the small picture as well as the big. I get very annoyed when someone mentions from out of the blue a third world problem to mute an otherwise sensible discussion. Or non-sensible for that matter. As if we should never be allowed to talk about anything else.

Btw - Luis CK FTW!

[Wo3Dan]

..... i'm seriously going to try to avoid getting into this again because last time around (this exact thread) i think i might of pissed off gerritt and that sucks.. he's one of my faves around these parts..
.......

Jeff, nothing of the sort. You need to do much more than that. I highly value your view/opinion on this matter. And we discussed it for a while. At some points we may disagree. At others I think you were right for what you are working on. You needed some tool that offsets and end in a different way. How I wish that there were true circles in SU or at least true construction circles. The latter would not make SU much heavier. At some point I left the topic for what it was, I think when TIG came to rescue with a new plugin to help you out.
Peace, man!

[TIG]

The native 'Offset' works just fine - within its own limitations.

My 'Smart_offset' removes reversed edges etc too but is otherwise the same creature...

'Offset' offsets Edges - that is all it does; it does not offset Arcs, except as if they were Edges.
This means that the two end-most segments of a bound set of segments [that you refer to as an 'Arc'] are offset quite logically by 'Offset', but that is just as if they were the equivalent selected Edges that had not been 'welded' into a bound-set to form that Arc.
So, 'Offset' ignores the bound-set's Arc-ness and always takes 'Edges'...
That's just the way it is.

If the native tool had been called more accurately 'Offset-Edges', then you shouldn't have been at all surprised when it didn't 'Offset-Arcs' !

There are regular gripes about SketchUp's lack of true Arcs and Circles - they are really special collections of bound Edges [forming the pseudo-Arc's segments].
I have made a several tools to compensate for some of these shortcoming - like TrueTangents and its siblings which allow you to find the 'real points' and not those from the intersections of lines and the Arcs' segments, which are always 'off'...

The very issue of Arcs offsetting as Edges prompted me to write this fix - 'Arc_offset_true' - earlier last year... viewtopic.php?p=395769#p395769
Because only 326 members [out of 155,000!] have downloaded it the 'clamor' for properly fixing this issue 'formerly' is hardly overwhelming

If you use my tool in the appropriate circumstances you will get correct 'offsetting' of an Arc at its ends - as in CAD, where 'true' Arcs are available [in my fix it's actually just a 'Scaled' copy of the original Arc, with the scaling done about the Arc's center-point and calculated so the resultant Arc is suitably sized so it's the required distance from the original - bearing in mind that means when measured from vertex-to-vertex, and not segment center-to-center as with the conventional Edge-Offset]: this method contrasts with using the native 'Offset' tool which will always offset the Arc's segments as if they were just vanilla Edges...
It would be nice if SketchUp included some better Arc tools... but until then there are many adequate workarounds [mostly made by me] !

So... the real title of this series of posts ought to be 'Native Offset handles Arcs as if they were Edges, not as Arcs... Help!'

[Alan Fraser]

TIG is perfectly correct (of course) The offset Tool works as an Offset Tool, not a Scale tool. In Olav's posted image above, you will find that the internal and external offsets are produced accurately; and the ends of those offsets are perfectly aligned with a perpendicular being drawn from the end points of the original arc.
Unfortunately, the consequence of the original arc not being a true curve, but a series of straight edges, results in these new end points not being aligned with the centre of the original arc.

Think of it this way; if the original arc had been a full semicircle, then the ends of the two offsets would be expected to be lined up with the ends of the original. In other words, all 3 arcs sharing the same baseline. However, because the curve is segmented, the only way this is going to happen is if the two end segments of the original arc are exactly parallel. You simply won't get this using the Arc Tool. You'd need to draw a full circle then rotate it so the the bisector ran through the mid point of two opposite and parallel edges....or use TIG's plugin.

It's effectively the same problem that is encountered when Follow Me is used along a curved path...the end faces may not be aligned exactly the way you would expect them to be on a true curve. It would be nice if both tools offered the plain vanilla and true-curve options.

[thomthom]

It's effectively the same problem that is encountered when Follow Me is used along a curved path...the end faces may not be aligned exactly the way you would expect them to be on a true curve. It would be nice if both tools offered the plain vanilla and true-curve options.

I'd argue that if it's a problem, which I happen to think of both these scenarios, it should be fixed. Make the computers do the work we want.

[Jeff Hammond]

That's just the way it is.

and you're ok with that? why?

If the native tool had been called more accurately 'Offset-Edges', then you shouldn't have been at all surprised when it didn't 'Offset-Arcs' !

wow..

The very issue of Arcs offsetting as Edges prompted me to write this fix - 'Arc_offset_true' - earlier last year... viewtopic.php?p=395769#p395769
Because only 326 members [out of 155,000!] have downloaded it the 'clamor' for properly fixing this issue 'formerly' is hardly overwhelming

maybe because it's not really fixing anything? i mean yes, you can select a single arc then use that ruby and offset it properly.. but what happens if you try to do something crazy-- like maybe another line is connected to the arc (i.e.-a very real world scenario)?? not much.. just the arc offsets and you still have to go in and manually draw things etc.. it just allows you to deal with sketchups shortcomings in a different order.. (normally, you have to offset the lines manually then fill in the proper arcs-- with the plugin, you offset the arcs first then go back and fill in the proper lines)

but that's beside the point.. the problem goes deeper than offsetting curves.. they are the easiest to fix manually but i use the offset tool as an example because it's the easiest to talk about since there's only a single curve involved..

to (try to) show the immensity of the problem, here's a drawing which shows how this same exact offset behavior causes the same exact problems in other tools.. and in geometry that is much slower to fix and/or draw manually..

every one of these examples is wrong.. (and if you're ok with saying "Well, that's just the way it is" then cool.. however, it doesn't change the fact that these are all wrong'

theyareallwrong.jpg

but until then there are many adequate workarounds [mostly made by me] !

TIG man, i'm sorry but none of them work right and more to the point, they only affect a few situations.. if the problem was fixed internally (in sketchup itself), you wouldn't need to attempt to 'fix' anything plus all these other functions would work right too..

So... the real title of this series of posts ought to be 'Native Offset handles Arcs as if they were Edges, not as Arcs... Help!'

no.. that shouldn't be the title.. again, i use arc/offset to illustrate the point in (what i feel should be) the simplest manner.. but when you start bringing more typical/complex geometry into play, that's when thing really start to go bad.. (or- if i offset an arc with su offset, i'm left with 10 or so vertices in the wrong place.. do the same thing with follow me and i'm left with 250 vertices in the wrong place.. use follow me on something other than a 90º bend and you're looking at potentially thousands of vertices in the wrong place)