Boolean Union vs Join

[TheRainKnight]

boolean union concerns solid surface, ie close polysurface. it calculate intersection and trim when solids are inside each other.

join two surfaces do not proceed any boolean operation. You join two surface on one or more edge. Allow you to perform some filleting edge work, or meshing work.

[Azeiku]

So, in the sense of open surfaces, join and boolean UNION basically do the same thing. For example, I have two flat rectangular surfaces that are coplanar and share an edge. I could use merge on this surface (a better option to join but it doesn't work for me on the current surfaces I have) but instead use boolean union. Now let's say I used the join command instead. Does this pretty much end in the same result? Just a form of grouping?

Thanks!

[TheRainKnight]

I'm not sure about the union working on 2 surfaces sharing a common edge. Use join. it's working. For sure. /

[andrewjohn81]

do NOT use boolean for anything but solids.

If you would like to see an example of what it creates then follow these steps:

-create a plane
-create another plane connecting it on one corner, but only roughly half way.
-fill the remaining corner using the _SrfPt command to make roughly 1 surface with one odd corner.

Now do your boolean union, should look fine for now.

-run the mergeAllSurfaces command on that object now.

Messed up, isn't it.

-now undo until just before your boolean.
-Join those surfaces
-run the mergeAllSurfaces command

Perfect. Now you see a little bit why not to use Boolean operations on nonsolid object.

The use for the boolean operations is just to help you with quickly splitting, deleting, and joining objects all in one step. If there is nothing to trim then you should use the Join command.
An extremely simple example would be creating a box, a sphere, making them intersect and using the booleanUnion. This just trims off the middle and joins it. I wouldn't be suprised if you looked at the script for that if that wasn't exactly what it was.

____________________________
edit:
the boolean union Does work on two coplanar surfaces, but often creates some nasty geometry

[7Stones]

Interesting!

I have used boolean operations to merge and trim open and intersecting surfaces with successful and useful results. In fact, I've seen it used in official or semi officail tutorials by the supposed experts.

I never would have thought to use it on two surfaces that share an edge.

[Glyptic]

Rhino has many strengths. How it handles Booleans is not one of them. Somebody might consider a sticky to address Booleans. Sooner or later, there will be a lot of posts about them here.
A couple of hints (I'm too tired to even start on this subject). Check your normals with the DIR command. They should all be pointing out. Figure out a way around trying a Boolean with coplanar surfaces (yes there are tricks, like moving something .0001 in. this way or that). Move isocurves so they are not at the intersection of surfaces to be Booleaned (there are probably exceptions to this, but its something to check when you have a problem).
Booleans and fillets can drive you crazy until you get a grip on them.
larry
ps Booleans basically trim and join at the same time. Sometimes, if you have to have things a certain way, its best to do it all "by hand" with trims and joins.

[KBOC]

I've always considered booleans in Rhino to be spectacularly good. I use them all the time.

[OamadeusO]

Once I sussed out to check the normals the booleans have been mostly ok for me. Check my WIP for the results.

There are times when it fails and I dont know why. If you look at the 3 rounded rectangle cutouts on the blade the right and middle one worked first time the left one failed even though the normals were ok. I remade the shape and re extruded it and this time it worked...

[KBOC]

except when surfaces or edges meet, shownakededges has never failed to tell me where problems are if booleans fail.

[andrewjohn81]

I noticed Glyptic said that sometimes you have to do booleans by hand.
I almost never do booleans. It's bad habit from originally being a poly modeler (booleans should never be used there) but I'm starting to use them now.

Funny thing though. I was splitting, deleting, and joining surfaces yesterday to make a knob for a sink faucet. It was the little indentations on the cheaper kind of handles that go evenly all the way around. I made 10 of them and 8 of them would join, the other 2 wouldn't. So in this case doing it "by hand" didn't work.
I created a solid instead of just a surface, created the polar array again, did the boolean operations, and it worked perfectly.

It's always nice to have more than one way of doing things. I guess the more manual way isn't always the best. Usually it works better, but in this case it was the opposite.

[Glyptic]

When I have Booleans to do, I always try the native Rhino option first. If it doesn't work, I look for the obvious causes (including checking for proper intersections). If thats OK, and it still doesn't work, I'll go for the Npower Power Booleans. Still no luck, I'll do it by hand. I rarely need to opt for the third option.
One that Rhino has problems with is pipes of indentical diameter with a perfectly aligned orrientation. Npower can handle these. If thats not an option, you can split one pipe, then BU each "half". This is just one example where the Rhino toolset isn't set up to deal with it.
I've also read, but never tried, exporting the file as a V2, then import back into V3 and boolean then. V2 supposedly (I never used it) was better at Booleans than V3. I've read that several times.
Npower is a powerful plug-in and particularly useful for fillets (nearly always water tight) and booleans of all sorts). Its a bit pricey, but has saved me countless hours in the past year.
I often use it when I have 5-30 Booleans I wish to do simultaneously.
Hopefully V4 will not have as many problems as V3 in this regard.
Glyptic

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