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  1. #1
    Join Date
    Jan 2006
    Saumur, France

    Tutorial: Booleans – The Basics

    This Tutorial explains how booleans work, how to apply them, and how to tackle possible problems that come along when using them.

    1. What are Booleans?
    In Maya a Boolean is an operation that is performed one two objects to create a single compound object. You can apply three different types of Boolean operations: Union, Difference and Intersection.

    2. How do Booleans work?
    Applying a Boolean is quite simple. You select both objects and go to Mesh->Booleans and select which Boolean operation you would like to perform. If you are unsure which operation is the right one, do not worry – You can always change the type of Boolean in the channel box later on (Assuming you have history turned on).
    When applying a Boolean Maya takes into account the volume of the two selected objects and the space both objects might share. The easiest way to understand Booleans is to think of the operation as a Math Formula. The first selected object will be A, the second object will be B and the compound object after the operation will be C. So the formula goes like this: Object A (BOOLEAN OPERATION) Object B = Object C. This might seem confusing at first, but it will make a lot more sense once you have read the next section.

    3. What are the different Boolean operations?
    Cube and Sphere before Boolean Operation:

    Union: A + B = C. Union will combine the volume of both objects into a single object. It almost works like
    Mesh->Combine with the difference that Union will take out the shared space between object A and B.

    Difference: A – B = C. Difference will subtract the volume of object B from object A. Note that Difference only works if both object share space in between them. You could also say that you are using object B to drill a hole into object A. The shared space will be the drilled hole and object B will disappear completely afterwards. Keep in mind that selection order is of vital importance when using the Difference operation: First selected object is A, second selected object is B. If you are unsure which object you selected first take a look at the colors of your edges. Object A should be highlighted white, object B should appear green (assuming that you haven’t changed you Color output).

    Intersection: A % B = C. Intersection deletes both objects and leaves only their shared space. As the name of the operation implies object A and object B need to actually share space in between them – otherwise you will be left with no geometry after the operation has been performed.

    4. Things worth noticing when using Booleans
    - Maya creates a new shape node for the compound object, deletes the shape nodes of object A and object B, but leaves their transform nodes UNTIL history is deleted. That means you can still move both objects after the Boolean operation has been performed to change the outcome (Use the outliner to select the transform nodes).
    - History of object A and B will be combined in object C.
    - If you apply a Boolean to an object that has a Smooth Proxy on it, you will destroy the connection to the Smooth Mesh and you will have to reapply the Smooth Proxy.
    - It is not possible to use more than two objects for a Boolean. However you can get around this by combining multiple objects (Mesh->Combine) into a single object before applying the Boolean.

    5. Help, my Boolean operations are mixed up!
    You may have noticed that Booleans might behave irregular from time to time. It might look like the operations are mixed up. This usually happens when the Face normals of both object A and object B don’t point outward. If you don’t know what Face normals are then select both objects and go to Display->Polygons->Face Normals. Each face will now have a green line protruding from its center. If you see any Face Normals pointing inward (towards the center of the object) select their faces and go to Normals->Reverse.
    The irregular behavior usually occurs as described below:
    Face Normals point inward on both objects:
    - Intersection works like a Union
    - Union works like Intersection
    Face Normals point inward on one object and outward on the other object:
    - Union works like Difference
    - Difference works like Union

    6. Help, both objects disappear after I use Booleans
    Sometimes when applying a Boolean both object A and object B just disappear and nothing else happens. This can be really frustrating and there are many possible causes for this problem. Try any of the following suggestions to tackle the problem.
    - Try Mesh->Clean Up and set it to select Geometry only. Check for Nonmanifold Geometry, Lamina Faces and Edges with Zero Length. Do the proper Cleanup in case Maya has highlighted any areas on your geometry. If you want more information on Maya's cleanup funtion read this tutorial:
    - Select both objects and delete their history (Edit->Delete By Type->History).
    - Select both objects and freeze their transformation (Modify->Freeze Transformation).
    - In the outliner check if any of the objects are parented to anything they shouldn't be and unparent them if necessary.
    - Duplicate both objects and delete the originals. Try Boolean again on the duplicates.
    - Rename both objects.
    - Go to Display->Polygons->Border Edges in order to quickly find non merged vertices on your mesh. Merge all vertices that require merging.
    - If all fails you will have to remodel either object A or object B or possibly both objects. This can be a real hassle but to make life a little bit easier you can use your old faulty objects as a guide. Select the object in question, put it on a separate layer and set the view to Reference. You can’t select the old object but you can still snap to its edges and vertices which is a tremendous help when you have to remodel the entire mesh.

    7. I heard Booleans are bad – Shouldn’t I refrain from using them?
    You might have heard from other people that Booleans are bad, unreliable, messy, unpredictable etc. – opinions tend to differ on this subject. Aside from the occasional dysfunctional behavior Booleans have a tendency to create bad geometry. You might have noticed that your mesh ends up with N-Gons (polygons with five and more edges) after a Boolean operation. This doesn’t necessarily have to be a problem. For mere rendering purpose Maya doesn’t really care if your model is quadrangulated (meaning: All faces have four sides) or not. If you are modeling for a game you will definitely have to clean up your geometry, turning everything back to quads or tris. The pictures below show how you would go about fixing such geometry.
    Non Quad Shaded:
    Non Quad Xray:
    Quads Shaded:
    Quads Xray:
    Last edited by Count_Zero; 11-20-2007 at 07:07 AM.
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  2. #2
    Join Date
    Oct 2007
    well my stuff dont show up when ever iam using the reference squares has foot's
    its perfect with using centimeter's but when using foot in perpective view i need to zoom and still part wont show up unless i reall zoom and when looking from front view nothing appear's not even the default reference squares oh iam using windows xp 32 bit and autodesk maya 8.5
    can you please help mee fix this

  3. #3
    Join Date
    May 2014
    Perfect, I did it

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