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LineOnAreaOverlayer

Performs a line-on-area overlay. Each input line is split at any area boundaries it intersects, and attributes are shared between related lines and areas (spatial join).

Jump to Configuration

Typical Uses

  • Splitting lines where they cross the boundary of a polygon
  • Identifying which polygons contain or intersect lines
  • Identifying lines that intersect or fall within areas

How does it work?

The LineOnAreaOverlayer compares lines and polygons, splitting the lines where they intersect with a polygon boundary. Each resulting piece receives the attributes of the area(s) it is contained in, and each containing area receives the attributes of the line(s) that either fall within or intersect it (a spatial join). Features also receive a count of the number of overlaps encountered.

Aggregates can either be deaggregated before processing or rejected.

ClosedExample: Overlaying lines on areas

In this example, we perform an overlay of bike path lines on neighborhood polygons. The source data looks like this, where the highlighted blue line is a bike path line feature that crosses from one neighborhood to another.

We want to accomplish two tasks in this example:

  • splitting the lines where they intersect with a neighborhood boundary
  • assigning new attributes (perform a spatial join)
    • add the neighborhood attributes to the bike path
    • add all of the contained bike path names to the neighborhood polygon as a list attribute

In the workspace, the bike paths are connected to the Line input port, and the neighborhoods are connected to the Area input port.

In the LineOnAreaOverlayer parameters dialog, we make the following selections:

  • Attribute Accumulation: Merge Incoming (this is the default). This will merge the attributes from the features on to each other, which will add the neighborhood information to the segmented bike paths. However, it does not add multiple attribute values, and so we also:
  • (Optional) Generate List On Output ‘Area’: This creates a list attribute on the output areas. By choosing Selected Attributes, and then PathName, only the bike path names will be added.

Viewing the output, we can see that the selected bike path (in blue) has been split where it crosses the neighborhood boundary, and the neighborhood attributes for Mount Pleasant have been added to it.

The containing neighborhood encountered 18 overlaps, and now has a list attribute containing the bike path names.

Usage Notes

Choosing a Spatial Transformer

Many transformers can assess spatial relationships and perform spatial joins - analyzing topology, merging attributes, and sometimes modifying geometry. Generally, choosing the one that is most specific to the task you need to accomplish will provide the optimal performance results. If there is more than one way to do it (which is frequently the case), time spent on performance testing alternate methods may be worthwhile.

To correctly analyze spatial relationships, all features should be in the same coordinate system. The Reprojector may be useful for reprojecting features within the workspace.

ClosedSpatial Transformers Comparison Matrix

Transformer

Can Merge Attributes

Alters Geometry

Counts Related Features

Creates List

Supported Types*

Recommended For
SpatialFilter Yes No No No
  • Point
  • Text
  • Curve
  • Area
  • Testing for the existence of spatial relationships between two sets of features, and routing them according to whether they pass or fail the test(s).
SpatialRelator Yes No Yes Yes
  • Point
  • Text
  • Curve
  • Area
  • Identifying the nature of spatial relationships between two sets of features.
AreaOnAreaOverlayer Yes Yes Yes Yes
  • Area
  • Finding polygon overlaps and extracting them into new geometry.
LineOnAreaOverlayer Yes Yes Yes Yes
  • Curve and Area
  • Finding intersections between lines and polygons, and splitting the lines where they intersect with the polygons.
LineOnLineOverlayer Yes Yes Yes Yes
  • Curve
  • Finding intersections between line features, splitting them, and generating new line geometry as well as points representing the intersections.
PointOnAreaOverlayer Yes No Yes Yes
  • Point and Area
  • Text and Area
  • Identifying points that fall within polygons, and merging attributes between them
PointOnLineOverlayer Yes Yes Yes Yes
  • Point and Curve
  • Text and Curve
  • Identifying where points fall on lines, and splitting the lines into new geometry.
PointOnPointOverlayer Yes No Yes Yes
  • Point
  • Text
  • Identifying points in the same location (within a tolerance), and merging attributes between them.
Intersector Yes Yes Yes Yes
  • Point
  • Text
  • Curve
  • Area
  • Finding intersections between all input features, regardless of geometry (optionally including self-intersections), splitting features, and creating new geometry.
Clipper Yes Yes No No
  • Point
  • Text
  • Curve
  • Area
  • Solids
  • Raster
  • Point Cloud
  • Comparing features against a set of Clipper features, and splitting the features at or along the Clipper boundaries. Outputs both new and untouched geometry, identified as either Inside or Outside the Clipper.
NeighborFinder Yes In some cases No Yes
  • Point
  • Text
  • Curve
  • Area
  • Identifying the nearest other feature(s) to each feature being considered, either in another set of features or within the same feature set.
TopologyBuilder Yes Yes No Yes
  • Point
  • Text
  • Curve
  • Area
  • Analyzing spatial relationships between features to compute topology, splitting features and creating new geometry representing topologically significant nodes, edges, and faces, with associated attributes.

* NOTE: Curve includes Lines, Arcs, and Paths. Area includes Polygons, Donuts, and Ellipses.

ClosedThe Effect of Spatial Transformer Choice on Performance

Spatial analysis can be processing-intensive, particularly when a large number of features are involved. If you would like to tune the performance of your workspace, this is a good place to start.

When there are multiple ways to configure a workspace to reach the same goal, it is often best to choose the transformer most specifically suited to your task. As an example, when comparing address points to building polygons, there are a few ways to approach it.

The first example, using a SpatialFilter to test whether or not points fall inside polygons, produces the correct result. But the SpatialFilter is a fairly complex transformer, able to test for multiple conditions and accept a wide range of geometry types. It isn’t optimized for the specific spatial relationship we are analyzing here.

With a SpatialFilter:

The second example uses a PointOnAreaOverlayer, followed by a Tester. The features output are the same as in the first method, but the transformer is optimized for this specific task. The difference in processing time is substantial - from 54.3 seconds in the first configuration, down to 13.7 seconds in the second one.

With a PointOnAreaOverlayer and a Tester:

If performance is an issue in your workspace, look for alternative methods, guided by geometry.

Configuration

Input Ports

ClosedLine

Line features against which the areas will be compared.

ClosedArea

Area features against which the lines will be compared.

Output Ports

ClosedLine

Line features which have been split at area boundaries, with attributes added according to transformer parameter configuration.

ClosedArea

Area features, with attributes added according to transformer parameter configuration. Geometry is unmodified.

ClosedCollapsed

If a tolerance is specified, line features which were smaller than the tolerance value collapse to a point and are output to this port.

Closed<Rejected>

All non-curve features input to the Line input port and all non-area features input to the Area input port are output to this port.

Rejected features will have an fme_rejection_code attribute with one of the following values:

INVALID_LINE_GEOMETRY_TYPE
INVALID_LINE_GEOMETRY_VERTICES
INVALID_GEOMETRY_DEGENERATE
INVALID_POLYGON_GEOMETRY_TYPE
INVALID_POLYGON_GEOMETRY_VERTICES
INVALID_POLYGON_GEOMETRY_DEGENERATE

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

ClosedTransformer
Group By The default behavior is to use the entire set of features as the group. This option allows you to select attributes that define which groups to form.
Group By Mode

Process At End (Blocking): This is the default behavior. Processing will only occur in this transformer once all input is present.

Process 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.

ClosedConsiderations for Using Group By

There are two typical reasons for using Process When Group Changes (Advanced) . The first is incoming data that is intended to be processed in groups (and is already so ordered). In this case, the structure dictates Group By usage - not performance considerations.

The second possible reason is potential performance gains.

Performance gains are most likely when the data is already sorted (or read using a SQL ORDER BY statement) since less work is required of FME. If the data needs ordering, it can be sorted in the workspace (though the added processing overhead may negate any gains).

Sorting becomes more difficult according to the number of data streams. Multiple streams of data could be almost impossible to sort into the correct order, since all features matching a Group By value need to arrive before any features (of any feature type or dataset) belonging to the next group. In this case, using Group By with Process At End (Blocking) may be the equivalent and simpler approach.

Note: Multiple feature types and features from multiple datasets will not generally naturally occur in the correct order.

As with many scenarios, testing different approaches in your workspace with your data is the only definitive way to identify performance gains.
ClosedParameters
Tolerance The minimum distance between geometries in 2D before they are considered equal, in ground units. If the tolerance is None, the geometries must be exactly identical to be considered equal. If the tolerance is Automatic, a tolerance will be automatically computed based on the location of the input geometries. Additionally, a custom tolerance may be used.
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.

Overlap Count Attribute The Overlap Count Attribute added to output linear features holds the number of area features that they were inside of. The Overlap Count Attribute added to output area features holds the number of linear features that they contained.
ClosedAttribute Accumulation

If attributes on the incoming and original feature share the same name, but are not geometry attributes that start with fme_, then they are deemed conflicted.

Accumulation Mode

Merge Incoming: The original feature will retain all of its own un-conflicted attributes, and will additionally acquire any un-conflicted attributes that the incoming feature has. This mode will handle conflicted attributes based on the Conflict Resolution parameter.

Prefix Incoming: The original feature will retain all of its own attributes. In addition, the original will acquire attributes reflecting the incoming feature’s attributes, with the name prefixed with the Prefix parameter.

Only Use Incoming: The original feature will have all of its attributes removed, except geometry attributes that start with fme_. Then, all of the attributes from one (arbitrary) incoming feature will be placed onto the original.
Conflict Resolution

Use Original: If a conflict occurs, the original values will be maintained.

Use Incoming: If a conflict occurs, the values of the incoming will be transferred onto the original.
Prefix If the Accumulation Mode parameter is set to Prefix Incoming, this value will prefix attributes that are being added to the original feature from the incoming feature.

 

Generate List on Output ‘Line’

When enabled, adds a list attribute to the Line output features, and the attributes of each area containing an output line are added to that line's list.

Note that no intersections between area features are computed.

‘Line’ List Name

Enter a name for the list attribute.

Note: List attributes are not accessible from the output schema in 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 'Line' List

All Attributes: All attributes will be added to the output Line features.

Selected Attributes: Enables the Selected Attributes parameter, where specific attributes may be chosen for inclusion.

Selected Attributes Enabled when Add To List is set to Selected Attributes. Specify the attributes you wish to be included.

 

Generate List on Output ‘Area’

When enabled, adds a list attribute to the Area output features, and the attributes of each line contained by an output area are added to that area's list.

Note that no intersections between area features are computed.

‘Area’ List Name

Enter a name for the list attribute.

Note: List attributes are not accessible from the output schema in 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 'Area' List

All Attributes: All attributes will be added to the output Area features.

Selected Attributes: Enables the Selected Attributes parameter, where specific attributes may be chosen for inclusion.

Selected Attributes Enabled when Add To List is set to Selected Attributes. Specify the attributes you wish to be included.

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.

ClosedHow 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.

ClosedContent 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.

Reference

ClosedRelated Transformers

AreaOnAreaOverlayer

Bufferer

Clipper

Intersector

LineOnLineOverlayer

NeighborFinder

PointOnAreaOverlayer

PointOnLineOverlayer

PointOnPointOverlayer

SpatialFilter

SpatialRelator

TopologyBuilder

Processing Behavior

Group-Based

Feature Holding

Yes
Dependencies  
FME Licensing Level FME Professional Edition and above
Aliases  
History  
Categories

Filters and Joins

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Examples may contain information licensed under the Open Government Licence – Vancouver