Performs a surface-on-surface overlay so that all input surfaces are intersected against each other and resultant surface features are created and output. The output surfaces can retain all the attributes of the input features in which they are contained.
All surfaces are broken down into faces. For example, a mesh is broken into faces, one face per mesh part.
Non-surface input features are not supported. Input collections of surfaces are automatically de-aggregated.
Input Ports
Surface
Surface features.
Output Ports
Surface
Surface features are output here.
<Rejected>
Non-surface features are output here.
Parameters
Group By
The default behavior is to use the entire set of features as the group. This option allows you to select attributes that define which groups to form.
Parallel Processing Level
Note: How parallel processing works with FME: see About Parallel Processing for detailed information.
This parameter determines whether or not the transformer should perform the work across parallel processes. If it is enabled, a process will be launched for each group specified by the Group By parameter.
Parallel Processing Levels
For example, on a quad-core machine, minimal parallelism will result in two simultaneous FME processes. Extreme parallelism on an 8-core machine would result in 16 simultaneous processes.
You can experiment with this feature and view the information in the Windows Task Manager and the Workbench Log window.
Overlap Count Attribute
The Overlap Count Attribute holds the number of input surfaces that contain each output surface. This count will be 1 or greater.
List Name
If a List Name is supplied, for each output feature, a list is created of all the attributes of input features that contain the output feature. A list with the same name is created for traits.
Note: Attribute lists are not accessible from the output schema in Workbench unless they are first processed using a transformer that operates on them, such as ListExploder or ListConcatenator. All attribute list transformers are displayed in the Contents pane of the Transformer Help under Lists. Alternatively, AttributeExposer can be used.
Enable Tolerance
If set to Yes, the Normal Tolerance in Degrees and Offset Tolerance parameters are enabled. If set to No, the two parameters are disabled.
Normal Tolerance in Degrees
Faces must be parallel before they are allowed to cut into each other. If two faces are nearly parallel with normals that are slightly apart, use this parameter to set a tolerance in degrees. The larger the value, the less parallel the faces would have to be while still considered parallel to each other.
Usage Tip: Use this parameter together with Offset Tolerance.
Offset Tolerance
Faces must be co-planar before they are allowed to cut into each other. If two faces are nearly co-planar, but are a small offset from each other, use this parameter to set a tolerance in ground units. The larger the value, the farther away the faces could be while still considered co-planar.
Usage Tip: Use this parameter together with Normal Tolerance in Degrees.
Example:
Usage Notes
When attributes (traits) are merged between features, existing attributes (traits) are not replaced. Therefore if the features being overlaid have attributes (traits) with the same name, then the first set of values will be kept. You can work around this by renaming, prefixing, or removing attributes (traits) to avoid name collisions.
Aggregates are not supported by this transformer.
Editing Transformer Parameters
Using a set of menu options, transformer parameters can be assigned by referencing other elements in the workspace. More advanced functions, such as an advanced editor and an arithmetic editor, are also available in some transformers. To access a menu of these options, click 
beside the applicable parameter. For more information, see Transformer Parameter Menu Options.
Transformer Categories
FME Licensing Level
FME Professional edition and above
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