NeighborFinder

In this example, we have a set of parcel polygons with no useful attributes, and a point dataset intended for labeling, with address attributes. We want to extract the addresses and apply them to the parcel polygons.

Though a PointOnAreaOverlayer would perform a similar comparison, it wouldn’t find a match where the point falls just outside the polygon, as in #1132. We will use a NeighborFinder.

The parcel polygons are routed into a NeighborFinder as the Base features - the ones that the transformer will try to find matches for.

The address points are connected as the Candidates - the ones that will be searched for a match, and will then supply the new attributes to the Base features.

In the Parameters dialog, Number of Neighbors to Find is set to 1, as we want only the single closest match to be used. Treat Polygons As is set to Areas.

Note that the default setting for Accumulation Mode - Merge Candidate - will copy the Candidate’s attributes onto the Base feature (which is what we want).

The output Matched parcel polygons now have attributes from their closest Candidate match.

Example: Finding all matches within a set distance

In this example, we have a dataset of bike path lines, and want to find drinking water fountains within 100 meters of the paths.

The bike paths are routed into a NeighborFinder as the Base features - the ones that the transformer will try to find matches for, and output.

The water fountain points are connected as the Candidates - the ones that will be searched for matches, and will then supply attributes to the Base features, as a list.

In the Parameters dialog, Number of Neighbors to Find is blank, and so no limit is imposed and all matches will be recorded. Maximum Distance is set to 100 (ground units, here in meters.)

By enabling Generate List and selecting specific attributes from the drinking fountain data, a list attribute will be added to the bike paths to store multiple matches.

One item is added to the _candidates list attribute for each match, as shown on the selected feature here. The list can be further manipulated to work with this information - see 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.

Base

Features to receive attributes from matching Candidates, according to the parameters defined in the transformer, and to be kept as output.

Candidate

Features that will provide attributes if they match the conditions defined. Candidates are not output.

In Candidates-Only mode (Input parameter set to Candidates Only), Candidates will behave as both Candidate and Base, and so will also receive attributes from matches and be output.

Matched

If a Candidate feature is found, then all the attributes from the closest Candidate feature are added to the Base feature and the Base feature is output via the Matched port.

If Generate List is enabled, either all or selected attributes from multiple matching Candidates may be added to a new list attribute.

In addition, several other attributes are added to the Base feature just prior to it being output via the Matched port:

Attributes	Description
_distance	The distance from the Base to the matching Candidate
_angle	The angle between the closest interpolated Base point and the closest interpolated Candidate point.
_closest_base_x, _closest_base_y	The coordinates of the closest interpolated point on the Base feature relative to the Candidate feature.
_closest_candidate_x, _closest_candidate_y	The coordinates of the closest interpolated point on the Candidate feature relative to the Base feature.
_candidate_angle	The angle from (_closest_candidate_x, _closest_candidate_y) to the next vertex within the Candidate feature. If (_closest_candidate_x, _closest_candidate_y) equals the last vertex of the Candidate feature, then candidate_angle will be the angle from the previous vertex of the Candidate feature to (_closest_candidate_x, _closest_candidate_y).
_candidate_label_angle	The _candidate_angle adjusted so that if it is used as a text rotation, the text will run from left to right. This angle is guaranteed to be greater than or equal to 270 and less than 360, or greater than or equal to 0 and less than or equal to 90.

All angles are measured in degrees counterclockwise from horizontal. Where angles are not well-defined (for example, when a Candidate polygon is contained inside a Base polygon), they are set to 0.

Diagram courtesy of Veremes

UnmatchedBase

If there are no Candidate features found to be within the maximum distance, then the Base feature will be output unchanged via the UnmatchedBase port.

UnmatchedCandidate

Candidate features not within the Maximum Distance to any Base feature are output via the UnmatchedCandidate port. Candidate features in excess of the Number of Neighbors to Find parameter will also be output here (only the first x number of matches will be used). If Generate List is not enabled, then any features within the Maximum Distance, but not closest, will be output from the UnmatchedCandidate port. This is because they are not used in any way; their attributes are not merged onto the base at all.

Invalid features are output via the <Rejected> port. Base and candidate features with null geometry will be rejected. Features with invalid geometries may also be rejected.

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

EXTRA_CANDIDATE_FEATURE
INVALID_BASE_GEOMETRY_VERTICES
INVALID_CANDIDATE_GEOMETRY_VERTICES
INVALID_GEOMETRY_VERTICES

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.

Input

Bases and Candidates - Accepts both Base and Candidate features (default). If a feature is routed to both the Base and the Candidate input ports, then features will be compared to themselves as they are both a Base and Candidate.

Candidates Only - Accept only Candidate features. There will be no Base input port. All Candidates will be compared with all other Candidates, but will not be compared to themselves.

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

Number of Neighbors to Find	The maximum number of Candidate features that will be included in the list specified by the Generate List parameter. The closest candidate features will be included in the list. If the value is 0 or blank, there is no limit to the number of neighbors that will be included in the list.
Maximum Distance	The Maximum Distance is measured in the units of coordinates of the input features. The list specified in Generate List contains all of the Candidate features that were within the Maximum Distance of the Base. Candidates exactly at the maximum distance will be included in the Closest Candidate List. If the value is 0 or blank, no limit will be put on the maximum distance.
Insert Vertex On Base Feature	If Yes, then (_closest_base_x, _closest_base_y) will be inserted onto the Base feature if the insertion is well-defined. For example, if a Candidate polygon is contained inside a Base polygon, insertion will not take place. If Yes, the _closest_base_x, _closest_base_y vertex will be inserted onto to the Base feature as well as added as an attribute. This option only applies to Lines, Polygons, Paths, Arcs, Ellipses, and Donuts.
Candidates First	If Yes, then all Candidate features must be input before any Base features. If a Candidate feature is input after a Base feature and this option is set to Yes, the Candidate feature will be ignored in all calculations.
Treat Polygons As	Lines: A polygon, donut, or ellipse will be treated as a line (that is, its boundary line) for backwards compatibility. Areas: A polygon, donut, or ellipse will be treated as an area, and any geometry that overlaps with the area will be of 0 distance away from that area.
Take Measures/Z From Candidate	If the candidate is a line, and the base is a point, this will specify if measures and z values should be copied from the candidate to the base. The z values will be equal to the interpolated z values at the point on the candidate that is closest to the base. The measures will either be interpolated or use the nearest known measure value, depending on the Treat Measures as parameter. If the candidate is not a line, or the base is not a point, this will have no effect.
Treat Measures as	If measures are being taken from the candidate, they can be treated as Discrete, meaning that they will be taken from the nearest known measure value on the candidate, or Continuous, meaning that they will be interpolated at the point along the candidate that is nearest to the base.

Attribute Accumulation

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

Accumulation Mode

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

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

Only Use Candidate: The base feature will have all of its attributes removed, except geometry attributes that start with fme_. Then, all of the attributes from one (arbitrary) candidate feature will be placed onto the base.

Conflict Resolution

Use Base: If a conflict occurs, the base values will be maintained.

Use Candidate: If a conflict occurs, the values of the candidate will be transferred onto the base.

Prefix

To prevent a Candidate attribute from being ignored because the Base attribute already exists, you can optionally specify a prefix that will be applied to each Candidate attribute when it is added to the Base. This parameter is only enabled when the Accumulation Mode is Prefix Candidate.

Generate List

When enabled, adds a list attribute to the Matched output features. This parameter is useful when the Number of Neighbors to Find is greater than 1.

Closest Candidates 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.

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 Professional Edition and above
Aliases	NeighbourFinder
History
Categories	Spatial Analysis

NeighborFinder

Typical Uses

How does it work?

Candidates Only Mode

Choosing a Spatial Transformer

Configuration

Input Ports

Output Ports

Parameters

Editing Transformer Parameters

Defining Values

Reference

FME Knowledge Center