Sketchup is Inacurrate???
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Don't be so theoretical, TT. "Enough" meaning the normal use of it starting from mechanical design to landscape/urban planning.
I have to say that for what I use SU - and that is somewhere between the scope of individual building architecture and landscape/urban size projects, it is accurate enough.
I noticed that when surveyors survey land and sites, their "accuracy" is somewhere within the 10 centimetre (~ 4") "tolerance". When I measure an existing building, even if it is new and (supposedly) was built as accurately as the bricklayers/builder can go, there's at least about 1-2 cm (~ 1 ") "tolerance", too.
Now why should my models be more accurate? (Of course, I can go for even more accuracy but other than getting things co-planar and arcs meeting in an arch, there's no reason for me).
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Point being is that in these types of discussions people tend to argue based on their own usage. Usage which often is never mentioned, so people argue on generic terms based on their specific experience. So two participants arguing their case can easily be both simultaneously right and wrong.
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Sorry for the question but as I never use with it
On a plotter (image above) circles from SU are transformed (postscript or other) or it's just like on the sreen so tiny segments ?
From Jeff's answer seems yes (tiny segts)... -
@unknownuser said:
Sorry for the question but as I never use with it
On a plotter (image above) circles from SU are transformed (postscript or other) or it's just like on the sreen so tiny segments ?
From Jeff's answer seems yes (tiny segts)...It's always segments as far as I know. Those circles in the mind of SU never translate into CAD circles. I find I have to redraw parts of an autocad export from sketchup because those line jagginess can look really awful on an otherwise smooth plot. Also, all the overlapping and partial line segments are just awful to work with. Don't know if Layout does anything different though, I don't imagine so.
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@thomthom said:
Enough for what
He he, yes I was being lazy with my words! "Enough" meaning - enough for the model to meet its ultimate purpose, as decided by the end user (or his/her client/customer).
As you also hinted - the original question is unanswerable because we do not know the purpose of the model - without this information no definitive answer can be given, nor can the OP gauge the usefullness of any advice offered.
The "universe" to "atoms" comparison is interesting - the units within SU are only notional, we are free to interpret the text labels as we wish. I could arbitrarily decide that the letter "m" really means miles or microns (or Mega light years!) if it made my model making more simple - and this would require no adjustment to the internal number representation of the software. In fact, we can see that this is even advisable sometime - use metres as a millimetre substitute to avoid the "small faces" problem. -
I don't have a problem with SU circles and arcs being a collection of tangents. I do have a problem with the Followme tool not being able extrude a face that is actually congruent to that collection. That, IMO, is an instance of what I would call inaccurate... as in wrong enough that I must do manual corrections to make it right.
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@genma saotome said:
I don't have a problem with SU circles and arcs being a collection of tangents. I do have a problem with the Followme tool not being able extrude a face that is actually congruent to that collection. That, IMO, is an instance of what I would call inaccurate... as in wrong enough that I must do manual corrections to make it right.
can you attach an example .skp to illustrate your issue?
(and yeah, I agree that there's all sorts of problems with follow me... I'm just curious as to what you're trying to do with it)
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Sketchup is inacurrate???
Hard to answer. As has been said by others here, it depends on what you model and on what you need as a result.
I read the question as: can you rely on SU if you know what you are doing?
Just saying that SketchUpâs limitation is 0.001 inch (0.0254mm) may be difficult to understand. Canât it do better than that? Is it realy that inaccurate?
See John Bacusâs answer in this thread: http://groups.google.com/a/googleproductforums.com/forum/#!searchin/sketchup/precision$2Binch$2Bjohn/sketchup/MqyEMnjVXjs/rVPdazWSUX4JAt first (at that time) I didnât fully understand the meaning of this threshold mentioned by John.
Precision goes way beyond that limit. (Although its setting only serves how to display dimensions, etc. It doesnât have any effect on the modeling itself.)Thomthom âprovedâ to me that SketchUp conciders length differences equal to or less than 0.001â as not existing.
To shed some light on what this threshold realy means when modeling I had to put some simple examples together in a model. Iâll share them (the model) here, together with some of my conclusions.
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SU canât have any two endpoints in the same context with a distance less than (or equal to) 0.001â.
So the shortest edge is 0.001â+⌠-
to model with smaller distances between certain objects you can go way below that 0.001â. But the geometry has to be split over different contexts (groups) to allow endpoints to come as close as 0.000001mm. This can be demonstrated by setting the precision to 0.000001mm.
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If somehow SU doesnât accept the small input that you wish to feed, move away first and then back by [same distance+small] input.
FAIK SU itself uses that high precision (and even higher) for correct intersections etc. This is (to me at least) very good to know. It gives me the feeling that at this point I can trust SUâs inferencing engine and what is under the hood.
Even if you model in mm or round inches or more, the program has to do its job at way higher precision to still give you an accurate model.
A (maybe not the best) example:
Think of a stairway, floor to floor 2.75m, 15 steps. => rise 183.333333mm
You may not want to know the rise in three decimals. Millimeters is enough to check its correctness. But itâs good to know that SU divides correctly. Now you donât have to care about chain dimensions. You can just measure from ground to any of these steps.p.s. I havenât played with angles in a similar way (yet).
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@unknownuser said:
@genma saotome said:
I don't have a problem with SU circles and arcs being a collection of tangents. I do have a problem with the Followme tool not being able extrude a face that is actually congruent to that collection. That, IMO, is an instance of what I would call inaccurate... as in wrong enough that I must do manual corrections to make it right.
can you attach an example .skp to illustrate your issue?
(and yeah, I agree that there's all sorts of problems with follow me... I'm just curious as to what you're trying to do with it)
Sure, I've attached an example. My work flow is to import a template of what I want to extrude along an arc, then create a circle of the required radius, use the protractor to measure off a set distance (n the example it is 20d), clean away what's not needed, select the line of the arc and hit Followme.
All you need to do is download the model, highlight the arc and use Followme on the vertical face standing at 0,0,0.
What you will find is none of the four corners of the extruded shapre are where they belong. The two corners closest to the center of the circle are farther apart than they should be and the two farthest form the center are too close together. The example has a set of faces that should be where the corners fall. You'll see they fall short or have pushed thru.
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Dave, I wouldn't extrude in that manner for complete accuracy. If I'm understanding the problem correctly, this is an example of the limitation of SU when it comes to aligning faces with the beginning and end of an extrude path. The face to be extruded is not fully perpendicular to the beginning of the path...as witnessed by the slight gap between the original template and the extrusion.
In these kind of situations you need something of a lead-in and follow-through to get the shape to extrude properly. I'd be thinking in terms of extruding along a greater section of arc, then trimming either end.Another solution is to edit either end of the extrude path so that it starts and finishes perpendicular to the existing faces. I have done this in the attached file. I have then welded the entire path back together with Recurve. You'll find that the profile now extrudes perfectly...even to cutting a hole in the diameter wall of the semicircle.
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@alan fraser said:
The face to be extruded is not fully perpendicular to the beginning of the path...as witnessed by the slight gap between the original template and the extrusion.
I think it is perpendicular Alan. The Y value of every point of the original face is zero... and so is the the centerpoint of the circle and the start of the arc. I'll recap my procedure:
- Place the face to be extruded at 0,0,0.
- Draw a vertical line up 2-5m from 0,0,0
- Draw aline on the dotted red axis of the necessary length -- in this example I used 100m
- Draw a circle at the end of the previous line, using a radius of 100m
- Change the number of segments of the circle from 24 to 360.
- Use the protractor at the center of the circle to map out 20d of arc.
- Draw a line from the center of the circle along the dotted line, intersecting the circle.
- Delete what is not needed.
- Highlight the arc.
- Use followme on the original face.
Considering the above, I see a mistake could be made at step 2, failing to draw a line on the axis, and at step 4, failing to center the circle on the endpoint of the line. Either would create an arc that is not perpendicular to the face. Wouldn't the proper quality check be to verify that both steps 2 and 4 have a Y axis value of 0?
I havn't had a chance to review the model you uploaded... I'll check later tonite or first thing tomorrow.
WRT your suggestion to use a lead in and follow thru, that is what I do and is what I had in mind when I wrote needs to be manually corrected. I have created several thousand of these extrusions... each one needing to be manually corrected. Either I'm using the tool improperly or it doesn't do what it is supposed to do.
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@genma saotome said:
...I think it is perpendicular Alan. ...
Both sides of the path are at an angle of 89.5 degrees (not perpendicular) to the connected faces. So the follow me starts and ends incorrectly.
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Let's keep in mind that it is called SKETCHup Not GoogleCAD.
SU was originally designed for architectural concepts, not as an engineering CAD.
Accuracy and precision in those fields take on totally different definitions.Yes, I use SU as a Pseudo-CAD because I cannot afford nor justify SOLIDWORKS for what I am doing.
It does the job real fine, but I wished it could do more, especially in the area of solids animation.I have to keep reminding myself constantly when defining my airplane parts that I an NOT making shop drawings; I DON'T have to concern myself with parts micro-fitting and dimensional precision beyond making it look right.
If it came to really making that airplane, I would be using SOLIDWORKS or more likely; CATIA, using my SU model as a CONCEPTUAL MODEL.
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@genma saotome said:
I do have a problem with the Followme tool not being able extrude a face that is actually congruent to that collection.
In the "DUH" thread this problem with Follow-me came up. Here is my (copied) reply.......
Re: The "Duh!" thread (aka the Doh! thread)
Postby jgb on Sun, 25 Mar 2012 12:03 pm
Another thing with Follow-Me I discovered a while back (and reported) is when you are defining a path that has curves, place the template face somewhere on a straight portion of any line segment, NOT at an endpoint.
If follow-me starts on an endpoint, the face template follows one of the subtended angles and royally screws up at the end, with an end face out of alignment. This is especially a major factor with closed loops.
However, if started on a straight section, it will end perpendicular to the last line of the path, and if the path is a closed loop, it will join properly.
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This is a good piece of advice. But would placing the profile on the segment rather than the vertex on a specified radius change the radius of the extruded figure somewhat, and thereby possibly creating a misalignment somewhere else?
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@jgb said:
Let's keep in mind that it is called SKETCHup Not GoogleCAD.
so going off that train of thought, I should just buy AutoCad then all my drawings will be done automatically.
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@mitcorb said:
This is a good piece of advice. But would placing the profile on the segment rather than the vertex on a specified radius change the radius of the extruded figure somewhat, and thereby possibly creating a misalignment somewhere else?
correct.
follow me simply doesn't recognize an arc if it's part of a path.. align the profile properly at one point on the arc will cause an error elsewhere.. and vice versa.. and there's no simple fix to or (other than using a plugin) -
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@genma saotome said:
@wo3dan said:
@genma saotome said:
...I think it is perpendicular Alan. ...
Both sides of the path are at an angle of 89.5 degrees (not perpendicular) to the connected faces. So the follow me starts and ends incorrectly.
Am curious how you determine that. Could you explain please?
Use the 'Protractor' tool constrained to blue (R/G plane) on the beginning endpoint of the path. Begin measuring the angle somewhere on/along the profile. End measuring the angle somewhere on the first arc segment. It measures 89.5 degrees.
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@mitcorb said:
This is a good piece of advice. But would placing the profile on the segment rather than the vertex on a specified radius change the radius of the extruded figure somewhat, and thereby possibly creating a misalignment somewhere else?
Yes, but that is a subjective "accuracy" syndrome.
SU creates arcs, curves and circles whose defined dimensions are at the endpoints of the segments, so anything dimensioned at the segments centerpoint will be not quite "accurate".
And until SU draws analog arc, curves and circles, rather than with digital segments, you can never get away without some inaccuracy of the extruded form.
The only way to avoid (minimize actually) this; is to create arcs, curves and circles with way more segments, which then creates a practicality problem.
Alternatively, create the extrusion face at a vertex/endpoint and then copy it to some position on the adjacent segment, keeping its origin point on the line.
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