View Full Version : geometry/boolean? problem

04-18-2007, 08:13 PM
I've attached a pic of what I'm trying to do. It seems like a boolean subtract is the correct process. But the results are ugly. Basically it's a rod being subtracted from a smooth tapered nosecone to simulate a counterbore for screws. From what I'm hearing, a boolean isn't the best choice here. Any insight would be great.......I'm a rookie.

is cineartist out there?


04-18-2007, 09:47 PM
The primary problem is that you're trying to do a boolean operation on a subpatched object, which is essentially a no-no, and will definitely give you weird results. Since you're smooth tapered object is symetrical, you may want to consider increasing the poly count of your smooth object, rather than subpatching. Then, the boolean operation is more likely to give you the results you're after.

Alternately, and likely more troublesome:
1. un-subpatch and original smoothed object (TAB)
2. quarter it
2. doing your boolean operation on the non-subpatched object
3. add edge reinforcement around the hole (this may be tough), but yo
4. mirror the object to reproduce all four segments
5. merge points so that you end up with one mesh, and
6. subpatch the final result.

The key to mixing hard and smooth edges with a subpatched object is ensuring that you've got sufficient edge reinforcement, so that you end up with "hard" edges around the hole(s).

Good luck...

04-19-2007, 02:25 AM
OK first just a quick explanation about boolean and subD with a very simple example.

You can't just boolean and then subD. First you would certainly want to merge points. But in this simple explanation there is another factor.

Picture 1

Simple boolean operation will be just a tunnel into the plane

Picture 2

The result. However, if you notice Add Edges tool will fail. This is because the polygon is half split.

Picture 3

You need to spit it again (select poly then select two points and ctl l to split) to complete this into two polys, then continue with the add edges tool to create the geometry then you can sub patch.

Picture 4

CC was used.

OK so that is a very simple concept of using boolean with SDS. For subd you have to create quads of course.

Next up, your particular case.

04-19-2007, 02:56 AM
Picture 1

OK so then I start out with two objects from my subpatch primitives file. One is the capsule and the second is a cylinder. ( I sized and stretched the cylinder) First picture is the cylinder arrayed to match up to the center of the polygons of the capsule.

This way both the boolean object and the capsule are already prepped for Subd.

Picture 2

preparing for boolean.

Pciture 3

The boolean subtract - don't forget to merge points.

picture 4

Split polygon with split tool.

Picure 5

Add edges tool and bandsaw pro to create the final geometry

After this it is subpatch and tweaking to get a curve.

Now the advantage of this method over multi shift is you have a ready made circle. You could alternatively draw this geometry on the mesh with the add edges tool then use extender or multi shift to bring it into the capsule. But for some things boolean is better.

04-19-2007, 03:13 AM
Now the last 3 pictures illustrate the idea that you can use the drag net tool (; on the keyboard) and RMB drag to adjust the circle for the right amount of fall off to then tweek the profile of the hole so that it has a curve in it. And then the final result of the hole.

This all relates to the basic principles of subD as expressed in the other threads I gave you and in the subpatch primitives object which if you study will show how this works to create smooth predictable, clean geometry with subD.

You of course have to connect the geometry now and make it all quads with the handsaw tool and add edges unless you are using CC and then your best judgment as to what needs to be subdivided. Then tweak as needed using point normal move and drag to bring the cap back to a round shape.

04-19-2007, 08:37 AM
Thanx guys,

Surrealist, your result is perfect! So should I be trying to keep the subtraction geometry (rod) inside a single poly as opposed to cutting through a shared edge? (see examples) I assume it would save time having to only dice up one poly. I'm going to practice dividing up a single poly tonight. I need to get this poly flow/split/merge/add edge/etc/etc... thing through my thick skull. At this point it seems like a lot of steps for a single hole. My examples are done in SolidWorks which treats everything as a SOLID as opposed to surfaces although it will do surfaces as well.

Thanks for the steps, hopefully I can learn them tonight. I know this situation will help in many other future cases.

04-19-2007, 11:57 AM
You can put it anywhere of course. Doing it in the middle of a polygon will help you with the curve aspect. That is, you will not have to go back and adjust the curvature of the capsule where you put the hole on the flat polygon. So that is a good idea.

However, the reason I did it the way I did was because of the fact that with boolean you have TWO sets of geometry to start. So if you try and do a boolean in the middle like that you will likely have to do some clean up because there will be an edge on the drill object that will line up with a point on the capsule. Or it will more likely be close and make a mess by putting extra points where you would not want them. So that is more work on that step.

SDS (Subdivision surface) modeling is an advanced technology over polygon modeling.

It is like this:

It used to be to get an organic shape you had do model then triple and subdivide in modeler so that in layout you had a nice smooth shape with polygons that had 3 sides and were not non-planar. A polygon render engine like Lightwave can not render polygons correctly if they are not 100% flat. And the only kind of polygon that is 100% flat at all angles is a triangle.

With this method your objects are of large polygon count in layout and you start adding more objects like this and the scene slows down and it is pretty impossible to work in layout.

With subdivision surfaces you are simply putting that burden on your computer at the render stage. You start out with a low poly object that is an approximation of the shape and when you hit render the computer takes over and not only smooths it but triples and subdivides. The degree that it does this you can control in the object properties panel under the geometry tab.

This opens the door to many possibilities in modeling and rendering that are not available otherwise. Not the least of which is creation of complex organic shapes and detailed creatures like you see being created with Zbrush. They use the concept of creating displacement maps applied to a subD object that the renderer uses to create fine detail with millions of polys.

Now the advantage of learning this method for things like drafting vis or arch vis is that you are not limited in the kind of detail and smoothness you can create on an object EASILY, once yo understand it. It opens the door for displacement maps for fine relief detail and also allows you to have hundreds of objects in your scene.

The trade off of using SDS is that you have to understand how to work the poly flow.

You can use the old school method of course and many do. In some cases this is the best choice. But there is no silver bullet.

Just also understand that the more complex your object gets the harder it will be to maintain the poly flow. This is why understanding the basics is essential.

Now you could go ahead and boolean that object and go with polygon modeling but sooner or later that is going to be limiting both in object creation and eventually in layout.

Once you learn SDS it is faster, smoother and all around holds more advantages than polygon modeling for most situations.

04-20-2007, 07:22 AM
I've figured out what I need...... a HELP file! Most programs have a help menu that has a content search. So for example: I make a poly and a disk to subtract from it. I subtract/merge points/split the poly. Then you mentioned the Add Edges tool, so I find that tool and have no idea what to select or do. I notice that it turns blue and when I click it shows some sort of coordinate.....? My point is that I can't just go to help and search Add Edges to find a short description of how to use it. My only option is to search for some tutorial or ask the forum. The interface doesn't tell you anything which makes what is simple into a mystery.

Do you know of a site or place I could find a traditional "help" file for LW? I'm looking for a list of tools and their functions. Am I missing something?

thanx for all the help

04-20-2007, 11:23 AM
Sorry, I assumed you knew about that tool.

What I did when I first got LW8 was I went through the entire manual for modeler, page by page tool by tool it took about a month full time!

But now with LW 9 there is a new help file. You have to have downloaded and installed these files. So make sure and go back to your CD and install it. I am not sure if it is on the download page.

If you have LW8 I think the PDF is the only available resource. You can download that from your registration page of LW8 or 9

Once you install the contents of the help file, in Modeler, you go to Help/Contents F1

Standard with most programs and you find a search function you are familiar with.

As to the add edges tool. The blue circles represent the center of that edge. Connect two circles to create a new edge and you can slide them around to position them. Slide it to 100% or 0% to connect it with an existing vertice. Open up the numeric panel (n) and chose release current if you make a mistake.

04-24-2007, 06:56 PM
Let me start with an overview of my project. Picture 1 is the device I am trying to model. Picture 2 is the solid model using SolidWorks. And then there's me.... My first attempt at modeling an object. Maybe it's a little ambitious but I figured the shapes are basic enough and why not model something useful to me. I work for a Sonar company designing this type of system. Although this is not work related, it would be nice to show them something cool.

Picture 4 is the area I would like to be able to do. The example you did was great, but in this example the rod is in the middle of 4 polys. I could reduce the cones segments but this will come up again so I'd like to learn.

Picture 5 is my poor attempt at dividing the polys and reinforcing the edges. Even though it might look fixable, the inside is corrupted. This rod had to split only 2 polys. So if I can learn to split 4 polys at compound angles I should be all set for a while.

04-25-2007, 03:04 AM
OK, now I understand towfish. :)

I would start by trying to simplify the mesh.

Your target should be the 8 sides of your bore object. So the hole should be 8 sides. If they don't line up you can merge polys or weld points or even create a new edge with the edge tool and then merge the polys that result. Don't forget to delete any extra points in the middle of the polygon that are left over after a merge.

Also make sure that the bore object is prepared at the end so that it will subpatch correctly. Maybe you wont see in there, I don't know. But if the bore is a subpatch object at least that eliminates the need to edit inside the hole after the fact. Look at my example.

And finally that is going to subpatch a lot better if you have a ring along the inside edge like in my example. You need something to hold the shape there or the subpatch will fold it in on itself. Think of those edge loops as anchors to hold the shape in place.

Colored areas should be merged to form 8 sides of your hole and surrounding mesh.

Alternatively you could first merge the polys of the tube object, so that none intersect, then boolean, then divide to connect back to the rest of the geometry..

04-25-2007, 03:16 AM
And one other thing. I am not sure what you did with the geometry but you should not have to move the points of the hole around. In the picture I notated it looks like you'd have to do that a little. Not sure from that angle.

Just make sure you keep the bore hole exactly as is was cut and merge the existing tube geometry to it. (without thinking I did that wrong in my example there) It will be easier to tweak those into shape than the hole back into a circle if you move those points at all.

04-25-2007, 03:34 AM
Corrected version. I think this matches what your object was but I am not sure. You get the idea.

05-02-2007, 04:26 PM

I just wanted to follow up with you. Realizing that I hadn't established any real fundamentals in LW modeling, I hit the books. I purchased Inside Lightwave 9 and also Dans DVD Signiture Courseware so far. I can't begin to tell you the improvements I've made (Thanx Dan!). I've finished the DVDs and I'm tackling the book. Between that and actually practicing (not to mention my full time job/life) it's crazy.... but I'm pretty much addicted to LW.

I do still struggle with certain things like keeping 4 point polys (and that whole boolean on a curve thing..) but I can prevent them at least some of the time now. I'm working on a simple character now with the box method and my goal is a short animation. This should be a good learning experience. I'll probably post questions to you in this thread if you don't mind. Unless I should do it somewhere else..

anyway, thanx for all your help

05-03-2007, 11:36 PM
Glad to see things are moving along.

For character animation, Timothy Albee's book is great.

Looking forward to seeing your work.

06-24-2007, 12:50 AM
Just wanted to let you know I finished a tutorial over at www.lightwiki.com

"Fundamentals of Subpatch Modeling"

You might find it useful as many of the techniques apply to creating inorganic models. In fact the whole boolean problem/solution was inspired in part by your post.

06-24-2007, 06:42 AM
Way too much info, just remember what "Boolean" means:


... if you cut into some tight geometry with a lower level in background, you logically don't get results.