Using Associative Dimensions

[irneb]

There are various reasons for using associative dimensions. Previously the DimAssoc setting only had a 0 or 1 value. This meant all dims were either created as "exploded" or as one unit. Very few people would even consider using DimAssoc=0 as the dimensions are then next to useless. With DimAssoc=1 the dimensions could be stretched and the value would adjust accordingly.

A few years back (about a decade or more) the DimAssoc=2 setting was introduced. When you change the setting in the Options dialog it actually toggles between DimAssoc=1 (off) and DimAssoc=2 (on).
DimAssoc2-Options.png

This "new" (read not too well known) setting causes some nifty feature in AutoCAD's dimensioning. Many would know this, but for those of us who don't here's a few examples of why you'd want it turned on:

Not using Annotative Scales
A lot of people have problems with using annotative scales. The only way to get around not using them would be to place all annotation on the paperspace, or creating several different textstyles and dimstyles - one for each scale to be displayed.

With model space dimensions you needed to either do your dims through a viewport (and have the DimScale=0 so it adjusts accordingly) or have several DimStyles (each with a DimScale for the intended viewport scale). Also you'd need to place relevant dims on a layer to VPFreeze them in viewports where they shouldn't be shown.
DimStyle-ToLayout.png

With paperspace dims you needed to have several DimStyles, each with a DimLFac to suit whatever viewport they will be drawn over. At least when placed on paper space you don't need to also have a set of layers so you can only show the relevant dim in its correct viewport.
DimLFac.png

There's a further problem with paperspace dimensions: You can't now edit the linework and have the dim changed at the same time. E.g. you can't use the stretch command to lengthen a rectangle and its dimension in one instruction. But also you need to go and adjust the dimension on paperspace each time the model is changed. This becomes a shlep, to say the least!

With DimAssoc=2 you have the best of both worlds. After you've edited the model, the dimension in paperspace adjusts to suit. But also, it now becomes unnecessary to fiddle with the DimLFac. Note this sample:

• The red dimension is drawn inside the model of the viewport, the brown as a paperspace dim over the viewport (both drawn while DimAssoc=1).
• The magenta dim is drawn inside the viewport and the maroon on top of the viewport, but both while DimAssoc=2.

DimAssoc-PS-Difference.png
Notice the difference? There's no need to adjust the DimLFac to 50.0 in the sample, as would be the case for the brown dimension.

Next post to show the "dynamicness" of associative dimensions.

[irneb]

Automatic updating of dimensions
When you edit the model space, it's easy to adjust the dimensions in one go. But also it's easy to see if a dimension isn't updated. It's not so nice when the dimension is drawn in paperspace though.

Here is that same sample, but with the windows both stretched to be 1200 wide:
capture_07222011_171057.png
Notice that it was "easy" to stretch the red dimension while changing the window itself. Not so for the brown though: here it needs to be edited on paperspace. Not too much of a hassle if it's only this one dim, but what happens if your drawing is more substantial that just this one instance? It could be very easy to miss a dimension ... not to mention, you're doing the same task twice!

However, notice that the magenta AND the maroon dimensions have updated without needing to adjust them at all. In fact I didn't even include the magenta dimension while adjusting the window.

... next, we'll look at how these work on blocks. In particular dynamic blocks.

[SLW210]

Looking good so far.

I may put this as a sticky in the beginners section, if no one objects.

[irneb]

Dynamic Blocks - Adjusting their parameters
While it's nice to be able to use things like stretch to adjust linework together with their dimensions, what about when you have to use another type of command? One where you cannot adjust the dimension in the same breath?

A prime example is dynamic blocks. It's possible to change the size of a dynamic block, but only through using its grips / changing the value of its parameters.

capture_07222011_172915.png

This shows the same drawing. But you'll notice the "windows" are actually dynamic blocks with height & width parameters. See how the "non-associative" dims (actually you could call them "half-associative" as they're not "exploded" ) didn't update when the window was changed to 1050 width?

Well, if this doesn't show a good reason to use DimAssoc=2, then perhaps when you work with xrefs will ...

[irneb]

Looking good so far.

I may put this as a sticky in the beginners section, if no one objects.

Thanks! I'm still bussy ... might be a while

[ReMark]

Looks like we have the makings of a winner. Keep up the good work irneb.

[irneb]

XRefs
Here I've attached a new drawing into the previous one. Not a lot of new stuff, but it shows that these dimensions also work on external linework. See this sample:

capture_07222011_174010.jpg

No real biggy! Let's open the other drawing and adjust the block over there:

capture_07222011_174629.png

And back to the original, reload ... and see what happens.

capture_07222011_174852.png

Oh-oh! Nothing's happened! Let's issue the DimRegen command as explained in the help:

capture_07222011_175012.png

Ahhh! Now that's more like it!

... now, as always, there's a "catch". AutoCAD wouldn't be interesting without any hiccups now would it?

[SLW210]

Moved to Beginner's and Stuck.

[Cad64]

Shouldn't this be in the Tips and Tricks section?

[irneb]

Tips'n'Tricks, Beginners, who knows!

Any how, to get on with it!

Editing the block
Seeing as this window is a slider, we'll add an arrow to indicate such. Let's do it in the original drawing first:
capture_07222011_180924.png

BCose & Yes for save! Now let's go and adjust one of those original windows.
capture_07222011_181028.png

Wonderful! It worked, the dims both updated from 1200 to 1350!

Now let's go and push AutoCAD to its "limits"! Let's go do the same thing with the block inside the XRef:
capture_07222011_180324.png
BClose, save ... and let's just (for the hell of it) change a window's size!
capture_07222011_180525.png
, close, save, reload & finally DimRegen!
capture_07222011_181923.png

Whoah! I broke it! Goes to show nothing in AutoCAD's "bullet" proof! From the help they do warn you that redefining a block will dis-associate these dimensions. Nowhere does it say a BEdit will not though! And no hope of being told it's going to break if you BEdit from inside the XRef!

BTW, a similar thing occurs when you redefine the block through Design Center. Everything not part of a changeable portion of the dynamic block (or if it's not a dynamic block - which isn't very interesting) won't break when you use Design Center to redefine that block. But when you insert from file & redefine, or worse explode and recreate, the dimensions become normal DimAssoc=1 types.

Of course there's the DimReAssociate command to go and fix these dimensions ... one at a time though! IMO, it's faster to just redo the dims!