split surface

 From:  Michael Gibson
3408.6 In reply to 3408.5 
Hi Luis,

> is there a difference between a boolean operation vs a
> trim to cut a line or a face? If so, what are the advantages
> of one vs the other? thnxs,

In some cases they can be equivalent, but in general the Booleans are more focused on operations between volumes or with curves the equivalent is operations involving closed curves.

Trim is more oriented towards cutting just the surfaces of an object and not preserving volumes.

If you want to work at more of a surface level where you're going to be cutting surfaces up and then joining them later on to make a solid, that's when you'll more often want to use Trim rather than the Booleans.

If you're working with solids and you want to cut a solid up and have the result be a solid, that's when you want to use Booleans instead.

There is some overlap between them though, because the Booleans are sort of like a batch combination version of trimming, where it does trimming + throw away pieces + joining for you as a kind of batch operation.

Here's a bit of illustration to show the different results between Trim or Booleans when solids are involved.

Here's a sphere and a line to cut it:

If you do a Trim, the sphere surface is cut and results in 2 surface fragments (I separated them slightly so you can more easily see):

But when doing a Boolean Difference (or Merge also for this case will produce the same result) the result is 2 solid pieces, where the extruded pieces from the line become part of the result:

Trimming is a somewhat more "low level" mechanism that you tend to use when working more with surface modeling techniques where you kind of work at generating the skin of an object and then join it together at the end.

It can be good to try to work more with solids and booleans when possible though, it can save time because pieces get combined together without extra steps, like in the example above when doing a boolean I don't have to do any extra steps to generate a cap surface to make each of those halves into a solid.

You can mix and match between these techniques though, by using Edit > Separate you can break a solid into individual surfaces and use surface modeling techniques, and you can use Edit > Join to glue together individual surfaces into a solid and then use solid modeling techniques with it after that.

But often staying more in solids can be more efficient.

- Michael