Sketchup is Inacurrate???

[thomthom]

@wo3dan said:

Btw, anyone noticed that there's no copy tool in SketchUp, ..... unless you know where it is hiding, .... in a move tool.

And explicitly labelled in the Edit menu. Though Ctrl+Move is much more powerful when you know about it. What I find more hidden is mirroring in SketchUp, which is either inversed scaling - or as "Flip along Axis" via the context menu. I don't really understand the choice of using "Flip" instead of "Mirror", as it appear that most applications use the term "Mirror". Keeps the UI simple, fair enough. Though occasionally it feel it's cut a little too close to the bone.

[dale]

This has been a really interesting, and passionate discussion, and I do think it worthwhile to, while confessing to totally love SketchUp, come clean with some of its flaws.
The reason this is important to me, is I have begun to get my prime contractors, my colleagues,(and I'm working on some consultants), to start dealing directly with my SketchUp models. This means I have to be really, really accurate with what I an sending them.
For some it may be they can just zoom in to see how I have solved particular framing. or structural scenarios etc., for others it means that they can go into the model and take direct measurements.
For me it means that I can express exactly what I wish to achieve, and don't have to rely on my contractor to make that decision, sometimes with different results.
I would like to also address the implied accuracy of Cad drawings. In my experience there are a lot of very bad Cad drawings. This is of course can directly attributed to the practitioner, but even in the case of reasonable Cad drawings the contractor is reliant on the measurements placed into the drawing. The measurements are not always relevant to the contractor, and sometimes I swear have more to do with the aesthetics of the drawing than the requirements to construct. Hence the dreaded onsite scaling.
Unlike Jeff, I don't often have to deal with the complexities of curves, as most of my work falls into the rectilinear house category.
But it still would be nice to have some of the issues in this thread discussed and addressed.
Great dialogue.

[pbacot]

Dale:"The measurements are not always relevant to the contractor, and sometimes I swear have more to do with the aesthetics of the drawing than the requirements to construct. Hence the dreaded onsite scaling."

Good points. But this is really about the training and "smarts" of the draftsperson. If one is drawing plans for a wood frame building, one should learn how carpenters lay out a building, first-hand if possible.

CAD drawings serve two purposes. In the studio (computer) they should reflect measurements in the design, click on a door and it reads 36" wide or the nominal width. This allows subsequent users (or oneself) to track changes and calculate layouts with confidence.

On the other hand the drawing used in the field (up to now) just shows a door symbol and the dimension is written. The draftsperson gives the dimensions that are important to the design and hopefully of use to the builder.

So in the first case the accuracy of an arc may come into play, (but not in most buildings). In the second case, the length of the chord or whatever is written in, if needed by the builder.

[pbacot]

@thomthom said:

@wo3dan said:

Btw, anyone noticed that there's no copy tool in SketchUp, ..... unless you know where it is hiding, .... in a move tool.

And explicitly labelled in the Edit menu. Though Ctrl+Move is much more powerful when you know about it. What I find more hidden is mirroring in SketchUp, which is either inversed scaling - or as "Flip along Axis" via the context menu. I don't really understand the choice of using "Flip" instead of "Mirror", as it appear that most applications use the term "Mirror". Keeps the UI simple, fair enough. Though occasionally it feel it's cut a little too close to the bone.

I'd guess most CAD apps have both commands. Mine does. It is odd that there isn't a native mirror command. Or an "align".

These seem like basic arrange tools SU lacks. mirror, align, nudge. Sure the move tool does a lot, but these are quicker. I hear Dave's footsteps... so I'll say I've gotten used to the ways to do these things in SU and don't think about it much.

[jbacus]

Wow... just... wow! Twenty-one pages of discussion on the vagaries of SketchUp's curve interpretation. Jeff: we've discussed this before, on Reddit. As you may remember from that thread, I shared your opinion that SketchUp would be improved with the addition of 'true arcs.'

@unknownuser said:

I agree- that would be a nice thing to have in SketchUp. When we designed SketchUp's object model in the early days, the thought was to keep it as simple as possible- more native entities required more tools to create them. And the interactions between different entities (arc-line, for example) are more complex to manage. So we came up with the solution that is in place today.

In another life, I was a student of Descriptive Geometry, and I learned that there is nothing that can't be drawn with a compass and straightedge. SketchUp only has the straightedge... and I can see how that is a hindrance. There's no way to construct, for example, an arc-arc intersection in SketchUp.

I agree this would be a useful thing to add in SketchUp, but it isn't something that we could add quickly or easily. I'm keen to see how other folks here would use "true arcs" if we had them in SketchUp, too.

Over the years there have been numerous ruby scripts built that add to the utility of SketchUp arc and circle entities- "point at center" was one of the first scripts I remember seeing. There are, however, limits to what can be implemented through our API without native arc support. I hope we're able to address that one day, but such low level modifications to SketchUp's object model are not to be made lightly.

john
.

[jeff hammond]

@dale said:

complexities of curves

fwiw, that's what i've mostly been talking about all along but got lost along the way being stuck on arcs..
offset tool is the easiest to talk about.. so is an arc

if sketchup suddenly dealt with arcs properly but curves reverted to the old (now) behavior then really.. not much has improved.. because arcs are the easiest of curves to draw manually.. so yes, as long as things are straight or arcs in sketchup, it would be a great improvement..

but what happens if you have an ellipse? then it reverts to the old behavior? an ellipse which shows this behavior is worse then an arc doing it for two reasons.. it's harder to draw manually and the error is greater..

a few pages back with the ugly J part of the conversation, there was inadvertently an example of this.. when a circle exhibits this behavior, it's not obvious to the eye, you have to get in there and measure it.. with other types of curves which change in radius along their length, the error becomes noticeable to the eye alone because the error is so big..

when i said a while ago about which point the developers would need to draw the line as to when the behavior reverts, i wasn't saying stop at arcs and everything else is the same.. in my head, i was thinking about the issue of the endpoints of the curves.. so i don't know how they would/could figure out the ends but all the right info is in the middle parts of a curve..

[edit-- oh.. hi john.. so can you make that ^ happen real quick like? ]

and i'm not saying that in a lame sort of way.. i just mean.. is that crossing the line for sketchup/trimble/you guys?

[jeff hammond]

@jbacus said:

As you may remember from that thread,
.

ouch.

that's the smack in the face that i deserve from this thread.
John, i don't know what to say as far as me talking down on the suteam regarding not talking about this. i'm sorry

i completely forgot about that live chat day and i do sincerely apologize.

(but the rest still stands though )

[gilles]

@unknownuser said:

[–]jbacusProduct Manager http://www.reddit.com/r/IAmA/comments/u18do/wera_bunch_of_sketchup_developer_types/

"I agree- that would be a nice thing to have in SketchUp. When we designed SketchUp's object model in the early days, the thought was to keep it as simple as possible- more native entities required more tools to create them. And the interactions between different entities (arc-line, for example) are more complex to manage. So we came up with the solution that is in place today.
**In another life, I was a student of Descriptive Geometry, and I learned that there is nothing that can't be drawn with a compass and straightedge. SketchUp only has the straightedge... and I can see how that is a hindrance.**There's no way to construct, for example, an arc-arc intersection in SketchUp.
I agree this would be a useful thing to add in SketchUp, but it isn't something that we could add quickly or easily. I'm keen to see how other folks here would use "true arcs" if we had them in SketchUp, too.

I learnt this too, in this life years ago.
How can one imagine to make a soft like SU without circle and arc? The easy way or the lazy one?

@unknownuser said:

Over the years there have been numerous ruby scripts built that add to the utility of SketchUp arc and circle entities- "point at center" was one of the first scripts I remember seeing. There are, however, limits to what can be implemented through our API without native arc support. I hope we're able to address that one day, but such low level modifications to SketchUp's object model are not to be made lightly.

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

John Bacus

Make me smile

So John Bacus, what's cooking now?

[thomthom]

@jbacus said:

Wow... just... wow! Twenty-one pages of discussion on the vagaries of SketchUp's curve interpretation.

Got to do something while "it's rendering".

[jbacus]

@thomthom said:

@jbacus said:

Wow... just... wow! Twenty-one pages of discussion on the vagaries of SketchUp's curve interpretation.

Got to do something while "it's rendering".

heh. +1

[Alan Fraser]

Another of the quirks of the Arc tool...which is why I tend to use circles for laying out stuff like this. I reserve the Arc Tool for rounding corners, turning block ends into bullnose or rectangles into lozenges....or when 'looking good' is good enough.
The accuracy is actually pretty impressive, but I find it very odd that you get an utterly different result depending on whether you type the radius into the VCB (Measurements) or Entity Info. It would be really useful if you could inference off an established centre...something it seems to recognise if you go the Entity Info route.

---

[jeff hammond]

@jbacus said:

@thomthom said:

@jbacus said:

Wow... just... wow! Twenty-one pages of discussion on the vagaries of SketchUp's curve interpretation.

Got to do something while "it's rendering".

heh. +1

+21 more pages on the same (ok..not exactly the same) thing.. (still about circles, or lack of)
http://sketchucation.com/forums/viewtopic.php?f=15&t=44972

.

[jeff hammond]

@unknownuser said:

but what happens if you have an ellipse? then it reverts to the old behavior? an ellipse which shows this behavior is worse than an arc doing it for two reasons.. it's harder to draw manually and the error is greater..

here's what happens with an ellipse..

lips.skp

![the left one is a correct offset.. the right one is what sketchup gives upon offsetting 2'..

i'm out an 1 3/4" over a distance of 24".. i don't think anyone, even nick, can scoff at that error.. ;)](/uploads/imported_attachments/85qH_lips.jpg "the left one is a correct offset.. the right one is what sketchup gives upon offsetting 2'..

i'm out an 1 3/4" over a distance of 24".. i don't think anyone, even nick, can scoff at that error.. ;)")

[edit- and the same thing stands as previously mentioned in this thread.. if the user desires the results on the right (i.e.- consistent distance between the segments, then they would just make sure they're offsetting a series of edges as opposed to a single curve)]

[Wo3Dan]

@alan fraser said:

Another of the quirks of the Arc tool...which is why I tend to use circles for laying out stuff like this. I reserve the Arc Tool for rounding corners, turning block ends into bullnose or rectangles into lozenges....or when 'looking good' is good enough.
The accuracy is actually pretty impressive, but I find it very odd that you get an utterly different result depending on whether you type the radius into the VCB (Measurements) or Entity Info. It would be really useful if you could inference off an established centre...something it seems to recognise if you go the Entity Info route.

Alan, I'm not quite sure what you are trying to explain.
First of all I can't get Entity Info to show the (any) arc's length with that number of digits in decimals. Probably my fault, I was pretty sure it could be done.
When I scale up by 100x and once again by 100x, then I get the value ~ 14398966,3mm which is (obviously) 100x100 times your values.
Not scaled I get an arc length of ~ 1439,9mm

I draw a circle, second click (cardinal point on red). Then I take out a 165 degrees part. Result is arc A with incorrect chord length and correct arc length.
After rotating a copy of the circle by 0.5 degrees I'll get two endpoints lined up on same red value, to form the endpoints of the correct chord.

If I then copy this chord to the side, I can use the arc tool directly to this edge to create a correct segmented arc: click first > click second point > either type the correct radius [Enter] or click third point and type the correct radius [Enter]
Like other dimension input you can override the current units. So (since I usually use mm) I can type 50cmr. The resulting arc when scaled up is ~ 14398966,3mm

Using the incorrect chord (from circles segments midpoints) would lead to an incorrect arc.

edit: Notice that you can input either the bulge or the radius (include the r)!

[gilles]

I was telling me we should stop arguing about arcs, circles and curves in SU as they do not exist... just polylines and polygones, kind of arcs, circles and curves tells entity info.

[pilou]

for info with cms as Unity at the maximum of its precision for a circle of 50 cms
a nurbs program gives 143.9 896 632 cms

with mms as unity 1 439.8 966 322 mms

[Wo3Dan]

@unknownuser said:

for info with cms as Unity at the maximum of its precision for a circle of 50 cms
a nurbs program gives 143.9 896 632 cms

with mms as unity 1 439.8 966 322 mms

My $1 calculator(*) reveals 1439.98966329mm.
But what about how to get Entity Info to show better than ~ ____.9mm
I mean more digits after decimal point.

(*) apparently former owner had no use for the calculator anymore.

[Alan Fraser]

Gerrit, you can specify the number of decimal places in Model Info > Units.
You guys might find this handy.

[Wo3Dan]

@alan fraser said:

Gerrit, you can specify the number of decimal places in Model Info > Units.....
Yes, I know, and I've often set it to max decimals in mm (0.000000mm)
But it has no effect on what 'Entity Info' displays for the arc's length.
Only units does and I can't go "beyond" mm.

Thank you for the link. I was just looking for this one that I don't have on the labtop that I'm working from. It's faster than setting up a program (and altering!) in Excel. Am I lazy or not?

As for your previous post:

@alan fraser said:

The accuracy is actually pretty impressive, but I find it very odd that you get an utterly different result depending on whether you type the radius into the VCB (Measurements) or Entity Info. **It would be really useful if you could inference off an established centre...**something it seems to recognise if you go the Entity Info route.

Isn't that done by entering the radius in the 'Arc' operation? Instaed of entering the bulge? If you already have the chord!

[pilou]

@unknownuser said:

My $1 calculator(*) reveals 1439.98966329mm.

hum hum first number after the decimal point?

1439.8966322 mm mine
it's because the arc or any curves in this prog is "unwraped" by a plugin for have the length
So from an existing curve and not from a "calculator"

Maybe it's also an error of the "calculator"! Who knows?

I will investigate !