AreaBuilder

Creates polygons from topologically correct linear features.

Typical Uses

Creating polygons from linear features
Checking linear network topology

How does it work?

The AreaBuilder receives features with linear geometry (lines, paths, and polygons) and creates areas wherever the linework surrounds closed shapes.

Areas are output, as well as any geometry not used for area creation.

Attributes may be merged or dropped, or accumulated in a list attribute along with an optional direction attribute that records the orientation of the input features.

Output polygon boundaries may be either lines or paths that preserve the input segments. Where areas are contained within other areas, donuts may be created and the donut holes either output or discarded.

Stricter rules may be applied for successful area formation, including checking for continuous curve direction and internal edges (cycles).

Aggregate geometries are either deaggregated or rejected.

Z values are supported.

Preparing input features for the AreaBuilder

Input features must have clean topology or they will not be used and output as Incomplete. The AreaBuilder has snapping capability, but more pre-processing may be required.

Topology issues could be:

Features not terminating at intersections
Misaligned nodes
Overshoots/undershoots
Missing nodes at intersections

These transformers may be useful for pre-processing input features.

	Use This For	Description
Snapper	Snapping together misaligned nodes with more options than the AreaBuilder’s built-in snapping.	Brings lines, segments, end points or vertex points of features together if they are within a certain distance of each other and (optionally) if they have attributes in common.
Intersector	Splitting intersecting features, adding new nodes where necessary.	Computes intersections between all input features, breaking lines and polygons wherever an intersection occurs/
Chopper	Chopping geometry into two-point lines, without adding any new nodes.	Chops line, arc, path, or area features into smaller features based on number of vertices or approximate length.
LineExtender	Adding length to undershoots (followed by an Intersector).	Extends line, arc, or path features at both ends by a specified length.
TopologyBuilder	Building full topology on input features, which includes intersecting them.	Computes topology on input point, line, and/or area features, and outputs significant nodes, edges, and faces with attributes describing topological relationships.

Examples

Example: Building areas from a streets dataset

In this example, we have a set a street features and want to build area polygons from them.

Note that the selected street is a single linear feature for its entire length.

The features are routed into an AreaBuilder.

In the parameters dialog, the default Polygon settings are used.

A list attribute named Streets is added which will contain the name of all surrounding streets for each output area, as well as the line segment orientation.

The output is not very successful, creating only a few areas.

An Intersector is added, with default settings used.

Note that the intersected output features are now split wherever they intersect another feature.

The intersected features are routed through another AreaBuilder (and then randomly colored for illustration purposes).

The output is successful this time. Note the list attribute, containing the street names and geometry orientation.

Usage Notes

As input features must be topologically correct for AreaBuilder to create polygons, it can be useful for checking topology.
The AreaBuilder has some snapping capability, but the Snapper provides more snapping options.

Creating and Modifying Area Features

These transformers work with polygons in a variety of ways.

Area Transformers Comparison

Transformer	Use this to...	Transformer Description
Creator	Create one or more new features with area geometry (when Geometry Object is Polygon).	Creates features using the parameters supplied, and sends them into the workspace for processing.
AreaBuilder	Create areas from topologically connected lines where they form closed shapes.	Creates polygons from topologically correct linear features.
LineCloser	Create areas from individual linear features.	Converts a linear feature to an area by connecting the end point to the start point.
Dissolver	Combine touching or overlapping areas to create larger areas.	Combines overlapping and/or adjacent areas into larger contiguous areas by removing shared and interior edges.
AreaCalculator	Calculate areas.	Calculates the planar or sloped area of polygon geometries and adds the results as attributes.
AreaGapAndOverlapCleaner	Clean up overlaps and gaps to create contiguous coverage.	Repairs area topologies by resolving gaps and overlaps between adjacent areas.
AreaAmalgamator	Generalize areas.	Generalizes area geometry by connecting and combining neighboring features and/or filling in holes and details.
DonutBridgeBuilder	Convert donut areas to non-donut areas.	Adds internal edges to connect donut holes to the outer shell, producing a non-donut polygon.
DonutBuilder	Convert areas within areas to donut holes.	Cuts holes in area features where they fully enclose another area, creating donut polygons.
DonutHoleExtractor	Separate donut areas into their parts.	Separates donut polygons into outer shell and hole polygons.
HoleCounter	Count the number of holes in a donut area.	Retrieves the number of holes in donut polygons, storing the result as an attribute.
AreaOnAreaOverlayer	Find polygon overlaps and extract them into new geometry.	Performs an area-on-area overlay (intersection of polygons) so that all input areas are intersected against each other and resultant area features are created and output. The resultant areas can accumulate attribute from any overlapping polygons.
LineOnAreaOverlayer	Find intersections between lines and polygons, splitting either where they intersect.	Performs a line-on-area overlay, either splitting lines where they intersect area boundaries or subdividing areas where split by lines. Attributes may be shared between related lines and areas (spatial join).
PointOnAreaOverlayer	Identify points that fall within polygons, and share attributes between them.	Performs a point-in-polygon overlay. Points may receive containing area attributes, and areas may receive contained point attributes (spatial join).

Configuration

Input Ports

Output Ports

Parameters

Group Processing

Group By

The default behavior is to use the entire set of input features as the group. This option allows you to select attributes that define which groups to form – each set of features that have the same value for all of these attributes will be processed as an independent group.

No attributes other than the Group By ones will be carried across from the Input features to the output features.

Complete Groups

Select the point in processing at which groups are processed:

When All Features Received	This is the default behavior. Processing will only occur in this transformer once all input is present.
When Group Changes (Advanced)	This transformer will process input groups in order. Changes of the value of the Group By parameter on the input stream will trigger processing on the currently accumulating group. This may improve overall speed (particularly with multiple, equally-sized groups), but could cause undesired behavior if input groups are not truly ordered.

Polygon

Consider Node Elevation

Select an option for handling z values, if they exist:

Yes: Use x, y, and z coordinates to match node locations.
No (default): Only use x and y coordinates. If z values exist, they are processed according to Connect Z Mode.

Connect Z Mode

When Consider Node Elevation is No, select a method for handling z values if they exist.

Connect Z Mode

When viewed in 2D (ignoring Z), a path (which may define the border of a polygon) may appear to be closed as shown in the left figure below. This same path, when viewed in 3D, may appear to be open as shown in the right figure below.

To specify how (and if) paths should be closed in 3D, select one of the listed modes.

Mode	Description	Example
Extend	The Curve is extended so that all vertices are left at their original location.
Average	Subsequent vertices that are not connected, but share an x and a y value are combined into one vertex, whose Z value is the average of the original two.
First Wins	Subsequent vertices that are not connected, but share an x and a y value are combined into one vertex, whose Z value is taken from the first encountered vertex.
Last Wins	Subsequent vertices that are not connected, but share an x and a y value are combined into one vertex, whose Z value is taken from the last encountered vertex.
Ignore	Z values are ignored. No change is made to the way the nodes are connected.

Preserve Lines as Path Segments

Select a method for creating area geometry:

Yes: The area boundary is a path, preserving the input segments.
No (default): The area boundary is a line, unless a path is required due to varying properties such as traits or measures.

Build Internal Edges (Advanced)

Select an option for creating cycles in areas:

Yes: Cycles are allowable and may be constructed
No (default): Do not use redundant segments

A cycle is a line segment that occurs twice in the same polygon's boundary, once in each direction.

Note that areas with cycles may be considered invalid for other geometry processing or unsupported by some output formats.

Check Curve Direction

Select an option for evaluating the orientation of input features:

Yes: All input features surrounding an area must have continuous orientation, connecting tip-to-tail, in order to successfully create a polygon.
No (default): Orientation is not considered.

Aggregate Handling

Choose how aggregate geometries are to be handled.

Deaggregate: Decompose aggregates into their individual components. With this setting, the transformer might output more features than were given as inputs.

Reject: Do not process aggregates and output them via the <Rejected> port.

Create Donuts

When enabled, areas fully contained within other areas produce donut polygons.

The donut holes may be either kept or discarded. Donut holes that share edges are dissolved into larger holes.

Drop Holes

Yes: Polygons that are holes of another polygon are discarded..

No: Polygons that are holes of another polygon are output.

When disabled, all areas are output without holes, and containing areas are not considered.

Donuts and List Attributes: When list attributes are created on donut polygons, list items are included for all input features, including those that make up both the containing area and all holes.

Snapping Pre-Processing

Snapping Type

Select a method for the optional pre-processing of input features:

None	No pre-processing is done.
End Point Snapping	Snaps end points of lines together if the distance between them is within the specified Snapping Tolerance.
Vertex Snapping	Snaps vertices of lines together if the distance between them is within the specified Snapping Tolerance.

When two features are snapped together, the last feature (in order of processing) is modified to match the first.

Snapping Tolerance

When Snapping Type is End Point Snapping or Vertex Snapping, specify the maximum distance in ground units between points for them to be snapped together.

See Geometry Concepts > Tolerance.

Attribute Accumulation

Accumulation Mode

Specify how attributes are accumulated on areas:

Drop Incoming Attributes	The output feature will not preserve any input attributes.
Merge Incoming Attributes	The output feature will merge all input attributes.
Use Attributes From One Feature	The output feature will receive attributes from only one input feature.

Generate List

When enabled:

List Name

Enter a List Name to be created on each output feature, containing an element for each input feature which contributed to that geometry, in order of appearance.

This parameter can also be used to preserve attributes from input features.

Note List attributes are not accessible from the output schema in FME Workbench unless they are first processed using a transformer that operates on them, such as ListExploder or ListConcatenator. Alternatively, AttributeExposer can be used.

Add To List

All Attributes: Every attribute from all input features that created an output feature will be added to the list specified in List Name.

Selected Attributes: Only the attributes specified in the Selected Attributes parameter will be added to the list specified in List Name.

Selected Attributes

The attributes to be added to the list when Add To List is Selected Attributes.

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	Group-Based
Feature Holding	Yes
Dependencies	None
Aliases	Polygonizer PolygonBuilder
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.