Replaces area geometries with their centerlines or straight skeletons. This transformer works best with long, narrow areas.
Output Ports
Centerline
The centerline of the input feature will be output via this port. If the input feature is an aggregate, at least one part was successfully processed, and the algorithm fails to generate a centerline for another part, that part will be left unchanged.
<Rejected>
Features that cannot be replaced by their centerline will be output via this port.
Rejected features will have an fme_rejection_code attribute with one of the following values:
INVALID_GEOMETRY
INVALID_GEOMETRY_TYPE
INVALID_POLYGON
INVALID_ELLIPSE
INVALID_DONUT
Parameters
General
Mode
Approximate Centerline: A line is returned that approximates the shape of the original input, and is roughly equidistant to the boundaries on either side.
Straight Skeleton: Every edge segment of the input area’s boundary is moved inwards at a constant speed -- the intersection of the moving segments is returned as the “Straight Skeleton.” Note: this mode returns branches that will touch the edges of the original area.
Note: In the straight skeleton mode, the algorithm may take a long time to run on large or complex input features.
Usage Notes
- Input areas must not self-cross and the region covered by the area must be connected.
- Z coordinates are ignored by this transformer. All centerlines are 2D.
Example
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.
Defining Values
There are several ways to define a value for use in a Transformer. The simplest is to simply type in a value or string, which can include functions of various types such as attribute references, math and string functions, and workspace parameters. There are a number of tools and shortcuts that can assist in constructing values, generally available from the drop-down context menu adjacent to the value field.
How to Set Parameter Values
Using the Text Editor
The Text Editor provides a convenient way to construct text strings (including regular expressions) from various data sources, such as attributes, parameters, and constants, where the result is used directly inside a parameter.
Using the Arithmetic Editor
The Arithmetic Editor provides a convenient way to construct math expressions from various data sources, such as attributes, parameters, and feature functions, where the result is used directly inside a parameter.
Conditional Values
Set values depending on one or more test conditions that either pass or fail.
Parameter Condition Definition Dialog
Content
Expressions and strings can include a number of functions, characters, parameters, and more.
When setting values - whether entered directly in a parameter or constructed using one of the editors - strings and expressions containing String, Math, Date/Time or FME Feature Functions will have those functions evaluated. Therefore, the names of these functions (in the form @<function_name>) should not be used as literal string values.
Content Types
| These functions manipulate and format strings. | |
|
Special Characters |
A set of control characters is available in the Text Editor. |
| Math functions are available in both editors. | |
| Date/Time Functions | Date and time functions are available in the Text Editor. |
| These operators are available in the Arithmetic Editor. | |
| These return primarily feature-specific values. | |
| FME and workspace-specific parameters may be used. | |
| Creating and Modifying User Parameters | Create your own editable parameters. |
Dialog Options - Tables
Transformers with table-style parameters have additional tools for populating and manipulating values.
Table Tools
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Row Reordering
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Enabled once you have clicked on a row item. Choices include:
|
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Cut, Copy, and Paste
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Enabled once you have clicked on a row item. Choices include:
Cut, copy, and paste may be used within a transformer, or between transformers. |
|
Filter
|
Start typing a string, and the matrix will only display rows matching those characters. Searches all columns. This only affects the display of attributes within the transformer - it does not alter which attributes are output. |
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Import
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Import populates the table with a set of new attributes read from a dataset. Specific application varies between transformers. |
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Reset/Refresh
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Generally resets the table to its initial state, and may provide additional options to remove invalid entries. Behavior varies between transformers. |
Note: Not all tools are available in all transformers.
When combined with the Tester, this transformer enables FME to perform area generalization operations.
FME Community
The FME Community is the place for demos, how-tos, articles, FAQs, and more. Get answers to your questions, learn from other users, and suggest, vote, and comment on new features.
Search for samples and information about this transformer on the FME Community.
Keywords: abstraction simplification simplify centerline centreline CentreLineReplacer