FME Transformers: 2025.0
Replaces area geometry with its centerline or straight skeleton.
Typical Uses
- Simplifying area geometry
How does it work?
The CenterlineReplacer receives features with area geometry and generates either a centerline or straight skeleton. Donut polygons and aggregates are supported, and polygons must not self-intersect.
Modes
Centerline
Centerlines generally are better for long narrow polygons. The result resembles the shape of the input feature, and is approximately equidistant to the boundaries on either side.
Straight Skeleton
The area boundary’s edges are moved inwards, parallel to themselves. When they collide, the polygon is split, and the process continues. The paths traced by the vertices where edges meet are the skeleton.
Note that generating straight skeletons on complex polygons can require long processing times.
Examples
Example: Generating centerlines from river polygons
In this example, we have a set of detailed river polygons. Note the structure, with multiple discrete polygons instead of more complex donut polygons.
We want to simplify this to a single-line representation.
The features are routed into a CenterlineReplacer.
In the parameters dialog, Mode is set to Centerline.
The output features are linear.
The discrete polygons have produced centerlines that do not intersect, and they are perhaps more detailed than they need to be. Some pre-processing of the polygons - generalizing and dissolving - might produce better results.
Usage Notes
- A BoundingBoxReplacer using 2D Oriented Bounding Box may be useful in some cases.
- The Dissolver, AreaGapAndOverlapCleaner, and Generalizer may be useful for pre-processing polygons.
Configuration
Input Ports
Input
Features with area geometry, including aggregates and donuts.
Output Ports
Centerline
Features with line geometry according to parameters
<Rejected>
Features without valid area geometry are output via this port.
Rejected features will have an fme_rejection_code attribute with one of the following values:
INVALID_GEOMETRY_TYPE
INVALID_POLYGON
INVALID_ELLIPSE
INVALID_DONUT
Rejected Feature Handling: can be set to either terminate the translation or continue running when it encounters a rejected feature. This setting is available both as a default FME option and as a workspace parameter.
Parameters
General
|
Mode |
Select the type of centerline to generate:
See Modes above. |
Editing Transformer Parameters
Transformer parameters can be set by directly entering values, using expressions, or referencing other elements in the workspace such as attribute values or user parameters. Various editors and context menus are available to assist. To see what is available, click 
beside the applicable parameter.
How to Set Parameter Values
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.
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
Table Tools
Transformers with table-style parameters have additional tools for populating and manipulating values.
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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
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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.
For more information, see Transformer Parameter Menu Options.
Reference
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Processing Behavior |
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|
Feature Holding |
No |
| Dependencies | None |
| Aliases | CentrelineReplacer |
| History |
FME Community
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Examples may contain information licensed under the Open Government Licence – Vancouver, Open Government Licence - British Columbia, and/or Open Government Licence – Canada.