Replaces geometry with an arc described by the first, middle, and last vertices of the input feature.

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Typical Uses

  • Undoing arc stroking on circular curves

  • Simplifying or smoothing

How does it work?

The ArcEstimator receives vector features with three or more vertices and replaces their geometry with arcs defined as Arc by 3 Points, using the first, last, and middle (median) vertices of the input line feature.

This transformer has no parameters.

Ellipses will be converted to arcs, and arcs are passed through unchanged.

For more information on arc geometry and types, see Arc.


The ArcEstimator uses only three arbitrary points, and does not consider or weight any other vertices. It may not reliably reproduce the original geometry of curves that have been stroked.

It is most accurate for arcs that are circular (the primary and secondary radius are equal or nearly equal). Depending on the desired output, it may not be useful for interpolating curves along an irregular path.


Usage Notes

  • If the parameters for the desired arc are available as attributes on the feature (as Arc By Center Point), use a 2DArcReplacer or 3DArcReplacer.

  • The Curvefitter or a Generalizer using the Douglas With Arc Fitting algorithm are configurable and will generally produce better results for anything more complex than a simple circular arc.

Creating and Modifying Arcs, Circles, and Ellipses

These transformers work with arcs in a variety of ways.


Input Ports

Output Ports


This transformer has no parameters.

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.

Dialog Options - Tables

Transformers with table-style parameters have additional tools for populating and manipulating values.


Processing Behavior


Feature Holding


Dependencies None

FME Community

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Examples may contain information licensed under the Open Government Licence – Vancouver and/or the Open Government Licence – Canada.