ArcStroker

Replaces arc or ellipse geometry with interpolated straight line segments.

Typical Uses

Preparing geometry for transformation, reprojection, or formats where arcs are not supported

How does it work?

The ArcStroker receives features with vector geometry and converts any arcs to a series of interpolated line segments.

Ellipses are converted to polygons. Paths will have any arc segments stroked while passing through line segments unchanged.

The number of interpolated edges may be determined by:

Letting the ArcStroker choose a reasonable number (default)
Specifying an exact number of segments to create per arc (Stroke By > Number of Interpolated Edges)
Specifying the maximum distance the new line segments may be from the original arc position (Stroke By > Maximum Deviation)

This example shows a circular arc stroked with four (4) interpolated edges:

Examples

Example: Arc stroking methods

In this example, we have some transit lines which are composed of lines and arcs. We will stroke the arcs using different settings and examine the results.

The features are in a UTM coordinate system with ground units in meters.

The features are routed into an ArcStroker.

Default: ArcStroker chooses a reasonable number of edges

In the parameters dialog, the default settings of zero (0) interpolated edges are kept. The transformer will calculate a reasonable value.

The output feature, shown in blue over the original arc in yellow, is a line with 23 coordinates. Note that it tightly follows the original arc, and coordinate 4 is highlighted.

The line segments to either side of the arc have been passed through unchanged.

Specifying an exact number of edges

In the parameters dialog, the number of interpolated edges is set to 3.

The output feature, shown in blue with the original arc in magenta, is a line with three segments (and so four coordinates).

It visibly deviates from the original arc, but has few points and so will optimize storage and processing.

Specifying Maximum Deviation to tightly follow an arc

In the parameters dialog, Stroke By is set to Maximum Deviation, with a value of 0.1 meters. This will prevent stroked segments from being positioned more than 10 centimeters away from the original arc.

The output feature, shown in blue over the original arc in yellow, is a line with 44 coordinates. Coordinate 3 is highlighted.

This feature follows the original arc even more tightly than the default setting, producing nearly double the number of interpolated points.

Usage Notes

Maximum deviation is a measurement in ground units. Features with a geographic (lat/long) coordinate system may need to be reprojected before using this option.
To reverse arc stroking, consider using the Curvefitter or ArcEstimator.

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

General

Stroke By

Select a stroking method:

Number of Interpolated Edges	Creates a specified number of line segments per arc or calculates an appropriate number.
Maximum Deviation	Creates enough line segments such that the new geometry is entirely within a specified maximum distance of the original arc.

Number of Interpolated Edges

When Stroke By is Number of Interpolated Edges:

If zero (0), a reasonable number of line segments will be interpolated for each arc.
If any other positive integer, the specified number of line segments will be interpolated for each arc.

Maximum Deviation

When Stroke By is Maximum Deviation, specify the maximum distance in ground units that new geometry may be from the original arc.

If the this value is greater than the primary or secondary axis of the arc or ellipse, the stroked arc will have the minimum number of edges possible.

If less than or equal to 0, the value of Workspace Parameters > Translation > Stroking Tolerance is used. If that value is also less than or equal to 0, the transformer will use Number of Interpolated Edges > zero (0) instead.

Make Polygon Out of 360 Degree Arcs

If Yes, arcs with a 360-degree sweep angle are converted into polygons.

If No, they are converted into lines.

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.

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

Table Tools

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

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.

For more information, see Transformer Parameter Menu Options.

Reference

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

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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.