ArcEstimator

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

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.

Limitations

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.

Examples

Example: ArcEstimator results and arc shapes

This example illustrates the ArcEstimator results on various arcs.

Circular Arc

A circular arc, in which the primary and secondary radius are equal, is stroked and then estimated. The resulting arc is identical to the original.

Original Arc	Stroked Arc	ArcEstimator Arc

Elliptical Arc

This arc has the same primary radius as the circular arc above, but has a shorter secondary radius, producing an elliptical arc.

The estimated arc does not match the original.

Original Arc	Stroked Arc	ArcEstimator Arc

Stacking the original, stroked, and estimated arcs illustrates how using the first, middle, and last vertices of the stroked arc does not necessarily produce a good result. The more elliptical the arc is, the more variance there will be.

The Curvefitter would be a better choice here.

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.

Arc Transformers Comparison

	Function	Geometry Out	Z Coordinates
Creator	Creates one or more new features with arc geometry (when Geometry Object is an arc type).	Arc by center point Arc by center point with ends Arc by 3 points Arc by bulge Ellipse (Arc by center point)	Supported
2DArcReplacer	Replaces any existing feature’s geometry with a 2D arc.	Arc by center point	No
3DArcReplacer	Replaces any existing feature’s geometry with a 3D arc.	Arc by center point	Yes, at center point
2DEllipseReplacer	Replaces an existing feature’s geometry with a 2D ellipse or circle (closed arc).	Ellipse (Arc by center point)	No
ArcPropertySetter	Modifies an existing arc or converts a point to an arc.	Arc by center point Arc by center point with ends Arc by 3 points	Supported, at center and/or ends
EllipsePropertySetter	Modifies an existing ellipse (closed arc) or converts a point to an ellipse.	Ellipse (Arc by center point)	Supported, at center point
ArcPropertyExtractor	Extracts the property values that describe an arc’s geometry and stores them as attributes.	Arc by center point Arc by center point with ends Arc by 3 points Arc by bulge	Supported
EllipsePropertyExtractor	Extracts the property values that describe an ellipse’s geometry and stores them as attributes.	Ellipse (Arc by center point)	Supported
ArcStroker	Converts arcs and ellipses to lines or polygons by interpolating points along the arc.	Path Line Area	Supported
ArcEstimator	Replaces geometry with an arc described by the first, middle, and last vertices of the input feature.	Arc by 3 points	Supported
Curvefitter	Replaces lines or polygons with an optimal combination of line and arc segments, creating smooth curving lines.	Path Area Arc by bulge Line	Supported
Generalizer	Reduces point density on lines or polygons, fitting arcs where possible (When using Algorithm > Douglas With Arc Fitting (Generalize) ).	Path Area Arc by 3 points Line	Supported
MinimumSpanningCircleReplacer	Either replaces an existing feature’s geometry with circle that contains all of its vertices or extracts the circle property values into attributes.	Ellipse (Arc by center point)	No

Configuration

Input Ports

Output Ports

Parameters

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.

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.

Text Editor

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.

Arithmetic Editor

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

String Functions	These functions manipulate and format strings.
Special Characters	A set of control characters is available in the Text Editor.
Math Functions	Math functions are available in both editors.
Date/Time Functions	Date and time functions are available in the Text Editor.
Math Operators	These operators are available in the Arithmetic Editor.
FME Feature Functions	These return primarily feature-specific values.
FME Parameters	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

Row Reordering

Enabled once you have clicked on a row item. Choices include:

Add a row
Remove a row
Move current row up one
Move current row down one
Move current row to top
Move current row to bottom

Cut, Copy, and Paste

Enabled once you have clicked on a row item. Choices include:

Cut a row - delete and copy to clipboard
Copy a row to the clipboard
Paste a row from the clipboard

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.

Import

Import populates the table with a set of new attributes read from a dataset. Specific application varies between transformers.

Reset/Refresh

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.

Reference

Processing Behavior	Feature-Based
Feature Holding	No
Dependencies	None
Aliases
History

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 all results about the ArcEstimator on the FME Community.

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