Intersector

Example: Intersecting different geometry types - areas and lines

In this example, we start with a set of park polygons and bike path lines, and want to split the polygons where the lines intersect them. To do that, we will first use the Intersector, then build the segmented areas.

The first step is to route both datasets into one Intersector.

The default settings will produce the results we want.

The Intersector reduces all of the geometry to line segments, and creates nodes at the intersection points.

By routing only the Intersected features through an AreaBuilder and then filtering for Parks only, we end up with park polygons, split where the bike paths ran through them.

Example: Finding intersections and building lists

In this example, we start with a dataset of street centerlines. The street geometry is as contiguous as possible - the line segments are not broken at intersections, as shown here with a selected street highlighted in yellow. We want to create intersections, and find out which streets cross at those intersections, using a list attribute.

The street dataset set is routed into an Intersector.

In the Intersector parameters dialog, Generate List is enabled. The list is named Intersections, and one selected attribute - NAME - will be captured in the new list.

At each intersection of the lines, they are split, and a node is placed at the intersection. The nodes have a list called Intersections, which contains the NAME attribute we requested, as well as the angle and direction of line it is referring to.

The selected node shown here has four items in the list, as four line segments converge at that point - Haro St incoming and outgoing, and Jervis St incoming and outgoing.

The lists can be further manipulated - see About List Attributes.

Spatial 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.

The 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.

Input

Features to be compared for intersections. Point, line, and area features are supported.

Intersected

The intersected features are output to this port. If the List Name parameter was specified, these features will have an attribute containing their number of overlapping input features. They will also have all attributes of the original features.

Node

The locations of topologically significant nodes are represented by point features and are output to this port. The transformer parameters modify which attributes are included on the output features.

Collapsed

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

All null, surface, solid, raster, and point cloud features are output through this port.

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.

Transformer

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.

Parallel Processing

Select a level of parallel processing to apply. Default is No Parallelism.

Parallel Processing

Note: How parallel processing works with FME: see About Parallel Processing for detailed information.

This parameter determines whether or not the transformer should perform the work across parallel processes. If it is enabled, a process will be launched for each group specified by the Group By parameter.

Parallel Processing Levels

Parameter	Number of Processes
No Parallelism	1
Minimal	coresThe processor, or CPU, is the physical part of the computer that performs mathematical calculations. It is the most important part of a computer system. Traditional processors have only one core on the processor, meaning that at any given time, only one set of calculations is being performed. If a processor is dual-core, this means the single chip contains hardware for two processors, now called cores to distinguish them from the single chip, running simultaneously, side by side. (Source: http://www.ehow.com/facts_5730257_computer-core-processors_.html) / 2
Moderate	exact number of cores
Aggressive	cores x 1.5
Extreme	cores x 2

For example, on a quad-core machine, minimal parallelism will result in two simultaneous FME processes. Extreme parallelism on an 8-core machine would result in 16 simultaneous processes.

You can experiment with this feature and view the information in the Windows Task Manager and the Workbench Log window.

Input Ordered

No: This is the default behavior. Processing will only occur in this transformer once all input is present.

By Group: This transformer will process input groups in order. Changes of the value of the Group By parameter on the input stream will trigger batch processing on the currently accumulating group. This will improve overall speed if groups are large/complex, but could cause undesired behavior if input groups are not truly ordered. Specifically, on a two input-port transformer, "in order" means that an entire group must reach both ports before the next group reaches either port, for the transformer to work as expected. This may take careful consideration in a workspace, and should not be confused with both port's input streams being ordered individually, but not synchronously.

Considerations for Using Input is Ordered By

Using Ordered input can provide performance gains in some scenarios, however, it is not always preferable, or even possible. Consider the following when using it, with both one- and two-input transformers.

Single Datasets/Feature Types: Are generally the optimal candidates for Ordered processing. If you know that the dataset is correctly ordered by the Group By attribute, using Input is Ordered By can improve performance, depending on the size and complexity of the data.

If the input is coming from a database, using ORDER BY in a SQL statement to have the database pre-order the data can be an extremely effective way to improve performance. Consider using a Database Readers with a SQL statement, or the SQLCreator transformer.

Multiple Datasets/Feature Types: 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, using Ordering with multiple feature types is more complicated than processing a single feature type.

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

One approach is to send all features through a Sorter, sorting on the expected Group By attribute. The Sorter is a feature-holding transformer, collecting all input features, performing the sort, and then releasing them all. They can then be sent through an appropriate filter (TestFilter, AttributeFilter, GeometryFilter, or others), which are not feature-holding, and will release the features one at a time to the transformer using Input is Ordered By, now in the expected order.

The processing overhead of sorting and filtering may negate the performance gains you will get from using Input is Ordered By. In this case, using Group By without using Input is Ordered By may be the equivalent and simpler approach.

In all cases when using Input is Ordered By, if you are not sure that the incoming features are properly ordered, they should be sorted (if a single feature type), or sorted and then filtered (for more than one feature or geometry type).

As with many scenarios, testing different approaches in your workspace with your data is the only definitive way to identify performance gains.

Parameters

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.
Duplicate Nodes at Each Elevation	The creation of nodes can be calculated in 3D, if requested. Constructing nodes in 3D would mean that line segments would only share a node if they shared the same Z value at the point they intersected. Constructing nodes in 2D would mean that all intersecting segments would share a common node, regardless of their respective Z values. For example, a situation where two lines (that crossed) represented roads, where one road was an overpass above the other road. with differing elevations. If you constructed nodes in 3D, these two roads would not be linked to the same node where they crossed. Two nodes would be produced at the crossing point – each one with a different Z value. If you constructed nodes in 2D, these lines would both link to a common node, which would be present at the location where they crossed. In either the 2D or 3D case, the full dimensionality of the input is preserved in the output – 3D features are never converted to 2D. The 2D or 3D choice only indicates how the nodes are created and which lines are linked to them; it does not affect the dimension of the features that are output. Yes - Whenever 3D lines intersect at differing heights, two 2D nodes will be output via the Node port. Each node will have the same x and y coordinates, but a different node number. No - Whenever 3D lines intersect at differing heights, a single 2D node is output at the intersection point.
Separate Collinear Segments	If Yes - causes overlapping segments not to be merged into a single segment: one copy is output for each original feature sharing the segment. Each such segment will have the respective original feature’s attributes as its main attributes, and attributes from all other collinear features will be added as a list attribute, if the list name was supplied. When a coverage of polygons is input, the set of topologically significant lines which form their boundaries is output.
Split Self-Intersecting Features	If Yes - Self-intersections in the input features are removed by splitting the feature. No feature-to-feature comparisons are made. In this case, the value set to the Overlap Count Attribute will be the number of features that result from removing self-intersections. If the feature did not self-intersect, the attribute will be set to 1. If the segment had several overlapping input features, the attributes of each of the input features will be added to the feature in the list identified by List Name, if one was specified. In any case, each output feature is also assigned the attributes of one of its original input features. This transformer also adds a "direction" attribute for each attribute resulting from the List Name parameter, labelling it as same if the geometry is oriented in the same direction, and opposite if the geometry is oriented in the opposite direction to the current geometry.
Aggregate Handling	Deaggregate: All input aggregates will be deaggregated, and each split part will be processed independently. With this setting, the transformer might output more features than were given as inputs. Reject: All input aggregates will be rejected.
Treat Measures as	When new coordinates are added due to intersection, the measures at those coordinates are determined from existing coordinates. Continuous: New measures will be computed from a linear interpolation of the neighboring coordinates along that segment. Discrete: Measures will be set to the measures of the nearest coordinates along the intersected segment.

Output Attributes

Overlap Count Attribute

Names an attribute that will be added by the transformer, containing the number of collinear input lines that overlapped the output segment.

Segment Count Attribute

Names an attribute that will be added by the transformer, containing the number of segments into which the segment’s original feature was divided.

If an input feature was broken into n output segments, each of those segments will have an attribute named <attribute name> which has a value of n.

Node Number Attribute

Names an attribute that will be added by the transformer to all node features, containing a unique ID for each topologically significant node.

Attribute Accumulation

Accumulation Mode

Specifies how attributes should be accumulated.

Drop Attributes: All incoming attributes are removed from the features.

Merge Attributes: Merges all attributes from overlapping segments.

Use Attributes From One Feature: Takes all attributes from one representative feature.

Prefix

When Separate Collinear Segments is Yes, and Accumulation Mode is Merge Attributes, this value prefixes all incoming attributes on collinear segments. It does not affect node (point) output.

Generate List

When enabled, adds a list attribute to the output features, and the attributes of intersecting features are added to the list. Nodes will receive list attributes from all intersecting features, including direction and angle.

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. All list attribute transformers are displayed in the Contents pane of the Transformer Help under Lists. Alternatively, AttributeExposer can be used.
Add To List	All Attributes: All attributes will be added to the output 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.
Direction Attribute	An optional attribute to include in the generated list, which indicates whether the direction of that input feature has been preserved (using same) or reversed (using opposite) in the output feature.

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 - whether entered directly in a parameter or constructed using one of the editors.

Related Transformers

PointOnPointOverlayer

SpatialFilter

SpatialRelator

TopologyBuilder

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.
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.
Working with User Parameters	Create your own editable parameters.

Processing Behavior	Group-Based
Feature Holding	Yes
Dependencies
FME Licensing Level	FME Base Edition and above
Aliases
History
Categories	Geometries Spatial Analysis

Intersector

Typical Uses

How does it work?

Choosing a Spatial Transformer

Configuration

Input Ports

Output Ports

Parameters

Editing Transformer Parameters

Defining Values

Reference

FME Knowledge Center