I make a curve and I use extrude .. Then I use "show points" and make some changes... Everything is working ok.

After that, I pick both objects (curve and solid) and copy them to an other place because I want to change something. The solid doesn't move separetely from the curve.
The problem is that now, the new solids are not connected to the curves as they should be (since they moved together).
As I understood from an older post of mine, moving the solid breaks the connection with the curve that created the solid and there is no update.
I can't understand why it doesn't work now...

My purpose is to be able to make generally similar objects but with some small differences. What is the method for that?
I can imagine that copying the curve and then using extrude is the simple solution but what if there are 10-15 steps before copying?

Also, the connection is lost when I use boolean operations... For example I make a cylinder. I make a smaller one (not in the center so shell command is useless) and I use boolean->diff. to remove the second. If I want to change the shape of the big cylinder I can't. Why? nothing moved, but the curve is now useless.

< As I understood from an older post of mine, moving the solid breaks the connection with the curve that created the solid and there is no update.
I can't understand why it doesn't work now...
Indeed : that's the perfect example of a" breaking History" (named "Dynamic Geometry" in another prog)
You must don't move any solid from it constructor curves or makes any move of volume + constructor!
It's the hard rule: all must stay in place :)
But if you make that : select all the constructor first and move it, all moves with it and you don't lost the history :)

For the fun you can try that
On view Top draw a circle, on View Font draw a simple profil line
Call the Rail Revolve, Select the profil, clic the circle as rail
Now you can move alone the profil or circle and don't lost the history
if you call Show Points for modify the profil or circle :)
But don't move the "surface" !!! else History will be losted!

> After that, I pick both objects (curve and solid) and copy them to an other
> place because I want to change something. The solid doesn't move
> separetely from the curve.
> The problem is that now, the new solids are not connected to the curves
> as they should be (since they moved together).

Copy is different than moving as far as history is concerned - copy doesn't replicate the history of an object, instead the copy is itself another action that is part of the history chain.

Some actions have history updating turned off by default - copy is one of those, but you can enable it by selecting the object and doing Edit/History and click Enable updates.

So in this instance, after you copy the curve and the solid to a new location, select the newly copied curve and solid and do Edit/History and click Enable update. Now go back and move a point of the original curve - you will see the original solid update, plus the copied curve and copied solid will update as well. This is because the history of the copy operation is being applied.

So Transform/Copy allows you to set up clones of an object that will update when the original is edited.

There is a way for you to get the kind of copy with an individual replicating of the history though, that is by using Edit/Copy and then Edit/Paste instead - this doesn't create a new action in the history chain like Transform/Copy. So for example, select the curve and the solid, do Edit/Copy, then move the curve to your new location (the solid will follow it due to history), then do paste, and you should have two independent updating versions like you want.


> Also, the connection is lost when I use boolean operations...

Right, boolean operations are one of those operations that implicitly involve deleting an object and replacing it with a new one. This is different than extrude for example, which involves only creation and no deletion.

Here's the steps for why the boolean breaks history, the history looks something like this:

Curve object#1

Extrude - uses Curve object#1, produces Solid object#1

Boolean - uses Solid object#1 and solid object #2 - Deletes Solid object #1 & #2, and produces Solid object #3.

Ok, so now you are left with Curve object#1 and Solid object #3. Now when you edit the curve, MoI will look and see if there are any objects available that use it directly. It looks at Solid object#3, but it doesn't find curve object#1 referenced by it. It was only referenced by the objects that were deleted. This is the reason why operations that involve deleting objects break the history chain.

Please let me know if this doesn't make sense.

- Michael

> I have forgotten that :D
> Tricky use of the history fonction!

Another fun one to play with is doing Transform/Mirror, or Transform/Rotate with several copies (by checking Make copies). Select the results of the transform, do Edit/History and click Enable update, then move some points of the original object...

- Michael

< then move some points of the original object...
You have a march pass military :D