AreaGapAndOverlapCleaner

Categories

Data Quality

Geometries

Related Transformers

AreaOnAreaOverlayer

Snapper

Repairs area topologies by resolving gaps and overlaps between adjacent areas. An overlap occurs where two or more areas intersect each other, creating a region covered by multiple areas. A gap occurs where two or more areas fail to meet at a boundary.

Jump to Configuration

Typical Uses

  • Cleaning topology errors in a polygon coverage to create a single, continuous surface.

How does it work?

The AreaGapAndOverlapCleaner resolves the differences between adjacent areas, creating a topologically clean shared boundary by dissolving overlaps and filling in gaps between the polygons.

These operations are generally carried out within a specified Tolerance - the distance, in ground units - within which gaps are candidates for repair.

All processing within the Tolerance distance is automated. Processing outside of the Tolerance is performed according to the Repair Method parameter, which provides options for determining which polygons take precedence.

All overlaps are resolved, whether they fall within the tolerance or not. Gaps outside tolerance may optionally be resolved.

Tolerance may be set to any number zero (0) or greater, or calculated automatically. Setting Tolerance to zero will result in all overlaps and gaps being processed according to the Repair Method.

While all overlaps will always be processed, gaps outside the Tolerance will only be processed if the Fill All Gaps parameter is set to Yes.

Processing Behavior and Tolerance

 

Within Tolerance

Outside Tolerance
Overlaps Automatic According to Repair Method
Gaps Automatic Not processed
Gaps when Fill All Gaps = Yes Automatic According to Repair Method

Example

Usage Notes

  • Requires valid area geometries. For example, self-intersecting, or degenerate areas will not be properly repaired.
  • If a single area is input, it will be output unchanged.
  • The AreaGapAndOverlapCleaner may create spikes when merging large overlaps to adjacent areas. However, spikes smaller than the tolerance will never be created. If these spikes are not desired, try increasing the tolerance.
  • Donut holes, if not filled by another area, are considered gaps in the coverage. They may be filled in if overlapped.

Configuration

Input Ports

Only area geometries are accepted as input.

Output Ports

Features that have been cleaned are output via this port.

Geometries that collapsed within tolerance will be output via the Remnants port. Additionally, features that did not have any geometry left after overlap resolution will also be output via this port with null geometries.

Features with invalid geometries will be rejected and output via this port. Additionally, if the Repair Method parameter is Priority (Edge Preserving) or Priority (Area Enlarging), features with invalid priority attributes will also be rejected via this port.

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

INVALID_GEOMETRY_TYPE

INVALID_PARAMETER_PRIORITY_ATTRIBUTE

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

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.

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.
Tolerance

The maximum distance between geometries in 2D for inclusion in automated processing.

If Automatic, an appropriate tolerance will be assigned based on the input features. Automatic Tolerance values tend to be small, and can assist in preventing issues caused by using excess precision.

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.

Connect Z Mode

If applicable, select a method for handling z values.

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.
Measures/Z Conflict Value

This parameter specifies how to deal with geometries that have a measure, but are missing at least one value, or that have z values, but are missing at least one value.

None (Drop Values): Remove incomplete measures or z values.

Compute: Look at the values on either side of the missing value, and compute an estimate.

Custom Value: The missing values are filled in with the specified custom default value.
Treat Measures as When using the Compute mode to compute missing measure values, measures can be considered Continuous, and linearly interpolated from their neighbors, or they can be Discrete, and taken exactly from the nearest neighbor.
Fill All Gaps

Yes: All gaps in the coverage will be filled.

No: Only gaps within the tolerance will be filled.
Repair Method

Specifies how to resolve gaps and overlaps that fall outside the tolerance.

Given the following input:

Longest Boundary The polygon with the longest border length to the conflict will be chosen.
Random The polygon to merge a conflicting region into will be selected at random.
Priority (Edge Preserving) Allows control of the priority of individual polygons in the repair process. The boundary of the higher priority polygon is preserved in this mode. Gaps between polygons will be assigned to the lower priority neighboring polygon, and overlaps will be assigned to the higher priority neighboring polygon. This method is used in conjunction with the Priority Attribute parameter.

Yellow: Higher Priority
Blue: Lower Priority
Priority (Area Enlarging) Allows control of the priority of individual polygons in the repair process. The area of the higher priority polygon will be enlarged in this mode. Gaps and overlaps between polygons will be assigned to the higher priority neighboring polygon. This method is used in conjunction with the Priority Attribute parameter.

Yellow: Higher Priority
Blue: Lower Priority
Priority Attribute

The Priority Attribute should be a non-negative integer value, with 0 meaning highest priority. It is enabled when the Repair Method parameter is Priority (Edge Preserving) or Priority (Area Enlarging).

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.

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.

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

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.

Reference

Processing Behavior

Group-Based

Feature Holding

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

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