Autocad - User Coordinate Systems (UCS) and their effects on funtionality

Big Train James

Western Thunderer

Ever wonder why things don't behave as you would like in Autocad? Often it's a result of the current UCS. This video talks about the basics of setting the UCS and what effect the UCS has on the behavior and results of numerous commands.
 
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Brian McKenzie

Western Thunderer
James,
Would it be fair to say that when choosing a UCS, it is in effect selecting the plane to be drawn on (recognizing that coordinates are part of that drawing process)? This seems more complex than merely choosing planes - as the origin of the UCS may need re-positioning (or off-setting) on the new plane?
Can one select faces in the 3D model to set the desired UCS - without having to first choose from the extensive toolset in the ribbon? Apologies if you covered that in your video. It's always good to watch those who can drive their software without having to think about it.
Cheers,
Brian McK.
 

oldravendale

Western Thunderer
This is fantastic! I don't understand a word of it, (I'm trying) but this is just so Western Thunder. Thanks for the hours of work which have gone into spreading universal knowledge of a leading edge area of technical expertise.

Brian
 

Steph Dale

Western Thunderer
This is fantastic! I don't understand a word of it, (I'm trying) but this is just so Western Thunder. Thanks for the hours of work which have gone into spreading universal knowledge of a leading edge area of technical expertise.

Brian

Hehe, you can have a go if you like... ;)

Jim,
Just to echo Dad's comments; a very useful guide, thank you!

Steph
 

Big Train James

Western Thunderer
Brian McK,
I think it is accurate to equate choosing or setting a UCS orientation or position with establishing a construction plane in other software. I had meant to mention this in the video, and was considering a followup. Effectively the xy plane through the 0 z coordinate is the current construction plane, wherever the origin of the ucs is established. Unless a positive or negative z coordinate is specificed, all 1d (lines) and 2d (curves, rectangles, anything 2d defined by at least 3 points) entities will fall in the xy plane. 1d and 2d entities can be drawn in planes that are parallel to the xy plane without moving the ucs origin point, but the z coordinate must be specified either by keystroke or snapping to a point with a non-0 z coordinate. This is why I'm most often really interested in which way the z axis points, rather than the origin point or specifically which way the x and y axes point.

If you want to draw on a plane that isn't parallel to the current ucs xy plane, then you must re-orient the ucs, or switch to a different saved ucs. You can after all define and save any ucs in any orientation or position you like, and switch to it at will. What's interesting is that most often I really don't care where the ucs origin is, but rather only which way it is oriented. I have a tendency to draw wherever I like, or off of center lines, but if necessary use object snaps to put things where they need to be. Explicit positioning of the ucs origin is only truly relevant, to me anyway, if one prefers to establish points using absolute coordinates. I can't think of the last time I did that, so it isn't terribly relevant to me at all :oops:. In every instance I can imagine where I move, copy, stretch, slice, extrude, rotate, or otherwise manipulate an entity, I am doing so relative to the entity's beginning position, usually by entering a distance or by utilizing object snap points.

One can select faces or edges of a 3d model to establish the ucs. The toolbar is always an option, or it can be done from the command line with UCS-->Face-->select face. And then there is a Dynamic UCS capability wherein when enabled the ucs will automatically temporarily orient to local entities if you hover over them. I don't care for this functionality, as invariably in my experience the ucs changes to something that doesn't suit my purpose. Dynamic UCS can be toggled on and off, but I just turn it off permanently. Your mileage may vary.

Brian oldavendale,
Think of the ucs as a piece of paper on your desktop, on which you draw something like a circle. The desktop is equivalent to the xy plane in a ucs. Now hang a piece of paper on the wall and draw on that. The wall is now the equivalent of the xy plane in the ucs, but it is clearly not the same as the plane that is the desktop. The xy plane in any ucs, no matter it's orientation or origin point, is effectively the "surface" that all 2d entities are created on in autocad (excepting the note above about planes parallel to the xy plane), akin to writing on a tablet on the desktop or painting on a canvas sitting on an easel. There can only be one ucs in effect at any given time, but you can switch between any ucs as needed.

Just to recap, 1d objects like lines are independent of ucs orientation. 2d objects like curves or the base of 3d objects are created in the xy plane or a plane parallel to the xy plane. 3d volumes like boxes or cylinders will have their base geometry in the xy or parallel plane, with a height specified in the z direction. If you want to change the orientation of 2d or 3d objects when they are created, you have to first change the ucs to the proper orientation.

Jim
 
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Brian McKenzie

Western Thunderer
Thanks James,

I've got my mind adjusted to this aspect of AutoCAD now. At first the process seemed overly complex, but I can see by using 'Saved UCS' etc it can be speeded up, although I suspect it's using rather more mouse clicks than for other software. Better if it could establish a UCS (i.e. a working plane) with a single click to any existing model face.

Can you get rid of tessellation lines in AutoCAD? I dislike them showing up in CAD views in printed publications.

-Brian McK.
 

Big Train James

Western Thunderer
Brian,
As far as I can tell, you can establish a ucs with a single click to any existing model face. Unless we aren't talking about the same thing. Take a look in the video, where I set the ucs by selecting a face. If that isn't what you're after, we can explore further.

As far as tessellation lines, do you mean during hard output like a plot? Or do you mean in model space for a screen capture or similar? Any chance you have a screen capture of an example just so I can be sure what you're talking about?

Either way, there should be a way to get rid of the lines, based on what I have been reading on line.

Jim
 

geoff_nicholls

Western Thunderer
Although your thread title states autocad, the principle also applies to turbocad (though one would need to hunt for equivalent commands.)
 

Brian McKenzie

Western Thunderer
James,
A second viewing of the video allowed your instruction to sink in a little deeper. :thumbs: Yes, a UCS can quickly be established to an existing face. Some UCS options are new to me - such as creating one relevant to any odd screen viewing angle. Perhaps useful when things are getting a bit desperate! :) (I got off the update train about 2010).

This pic displays views with and without tessellation lines. From what I have read, there seems to be some variation in control of visibility, depending on type of AutoCAD output.
Tessellation Lines.jpg

New model product announcements in the magazines are often of CAD screen saves, usually with a full complement of tessellation lines. The CAD of your Barber freight car truck sideframe also has them. If you do a plot, do they disappear?

Thanks, Brian.
 
Tessellation lines

Big Train James

Western Thunderer
Brian,
Thanks for the graphic. It's clear we are talking about the same issue. I've taken a look around some of the cad support forums regarding tessellation lines. It seems they are an autocad annoyance with limited remedy available.

In model space, for the purposes of a screen grab, it would seem the only visual style without tessellation lines is the "Shaded" style. The tessellation lines seem to show in all other styles. This is without regard to setting "Isolines" to 0, or any other number. In paper space (or layout tabs in modern Autocad parlance), the plot visual style can similarly be set to Shaded, and there are no tessellation lines.

Below: Model space with visual style set to "Shaded", captured with the snipping tool:
x-sf-casting-rev.JPG

Paper space with visual style set to "Shaded", plotted to a jpg:
x-sf-casting-rev-ANSI-D.jpg

There is some faceting showing, which I expect can be fixed to some extent.

There may be other methods to get rid of the lines, based on what I see on the forums, but I wasn't able to achieve the desired result following the given instructions. Some of the methods are dated and clearly apply to much earlier versions of Autocad. A shallow dive didn't reveal an effective recent solution. There are commands such as "Flatshot" and "Solprof" which produce what amounts to a line drawing without tessellation, but at the same time without surfaces rendered they lack quite a bit of information. By the way, if you try these commands, I'd recommend saving your original file as something else first.

Jim
 
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