AreaGapAndOverlapCleaner

Repairs area topologies by resolving gaps and overlaps between adjacent areas.

Typical Uses

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

How does it work?

The AreaGapAndOverlapCleaner receives features with valid area geometry and cleans up shared boundaries by dissolving overlaps and filling in gaps between polygons.

Input aggregate geometry may be either deaggregated or rejected.

Z values and measures are supported.

Repairing Overlaps and Gaps

Overlaps and gaps are processed slightly differently.

Both use the Tolerance and Repair Method parameters to determine how they are resolved. Gaps are further handled according to the Fill All Gaps parameter.

Overlaps are all processed, all the time. If the overlap is within the Tolerance distance, the repair is done automatically. If the overlap is greater than the tolerance, the Repair Method choice is used.

Gaps within the Tolerance distance are repaired automatically. If Fill All Gaps is Yes, gaps greater than the tolerance are repaired according to the Repair Method choice. If Fill All Gaps is No, they are not repaired.

	Fill All Gaps	Within Tolerance	Greater Than Tolerance
Overlaps		Automatic	Per Repair Method
Gaps	No	Automatic	Untouched
Gaps	Yes	Automatic	Per Repair Method

Tolerance

Tolerance is a distance in the ground units of the features’ coordinate system. The choices are to enter a value or choose Automatic.

For most transformers with a Tolerance parameter, Automatic is recommended, but it is frequently not the correct choice here. Automatic will calculate a value that accounts for minute differences introduced by binary limitations, rounding errors, and the like (See Geometry Concepts > Tolerance). The calculated value is written to the log file.

Tolerance is always greater than zero.

Tolerance > Automatic does not consider the size of gaps and overlaps present in the data. For many use cases, this value is too small and an explicit value should be entered. The value should be guided by the nature of the input geometry (size of gaps and polygons) and whether you want the repairs to be automatically handled or determined by a specific Repair Method.

Repair Method

Gaps and overlaps greater than the Tolerance value are repaired according to the Repair Method:

Longest Boundary: Gaps and overlaps are allocated to the area with the longest boundary.
Random: Gaps and overlaps are allocated to areas selected at random.
Priority (Edge Preserving): Gaps and overlaps are allocated according to a numeric priority attribute:
- Overlaps go to the higher priority area.
- Gaps go to the lower priority area.
- The boundary of the higher priority area is preserved.
Priority (Area Enlarging): Gaps and overlaps are allocated according to a numeric priority attribute:
- Both overlaps and gaps go to the higher priority area.
- The higher priority area may be enlarged.

When using Priority methods, zero (0) is the highest priority. If there is a conflict where more than one area has the same priority, one is selected arbitrarily.

Examples

Example: Using appropriate Tolerance values

In this example, we have a set of parcel features, separated in places by roadways and lanes.

On close examination, the data is not clean and needs to be repaired. There are random overlaps and gaps.

Note that this laneway is approximately 6 meters wide. It a valid gap that should be preserved.

Tolerance: Too Large

The features are routed into an AreaGapAndOverlapCleaner.

In the parameters dialog, Tolerance is set to 20 (meters, in ground units). Fill All Gaps is No, so that only gaps within the tolerance will be repaired.

The results are not good. As the tolerance is wider than the valid gap, the laneway has been filled in, crookedly.

When tolerance is too large, unpredictable results occur, including spikes, deformed shapes, and valid areas filled in.

Tolerance: Just Right

The features are routed into an AreaGapAndOverlapCleaner.

In the parameters dialog, Tolerance is set to 2.5 - a value that is less than the width of valid gaps, but large enough to capture the errors.

Gaps and overlaps are repaired.

Valid gaps are preserved and feature shapes are intact.

Example: Using Priority to determine gap and overlap allocation

In this example, we have two datasets with area geometry - zoning polygons and two-line rivers. Note that the selected zone polygon has a PRIORITY value of 1.

We want contiguous coverage, with the zones meeting the river’s edge.

On closer inspection, the two datasets do not meet smoothly. There are gaps and overlaps. Note that the river polygon has a PRIORITY value of 0.

We want to clean up the data and preserve the shape of the river polygons - not adjust the river to the shape of the zones.

Both datasets are routed into AttributeCreators to add their PRIORITY value, and then on to an AreaGapAndOverlapCleaner.

In the parameters dialog, Tolerance is set to Automatic. This will compute an extremely small tolerance number (see Tolerance above).

All of the visible errors will be much larger than this tolerance, and so will have the Outside Tolerance Parameters applied - Fill All Gaps, Repair Method, and Priority Attribute.

Repair Method is set to Priority (Edge Preserving), with the PRIORITY attribute chosen.

Zero (0) is the highest priority.

Overlaps are absorbed into the river, and gaps are added on to the zones. The shape of the river is preserved, and the coverage is contiguous.

Usage Notes

When unexpected results are output, it can often be corrected by adjusting the Tolerance value.
To repair only overlaps (not gaps), consider using a Dissolver.
Invalid area geometry such as self-intersecting or degenerate polygons will not be rejected, but will not be repaired properly.
Donut holes are gaps, and may be processed accordingly.

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 features as the group. This option allows you to select attributes that define which groups to form.

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.

General

Tolerance

Specify the maximum distance (in ground units) between geometries in 2D for features to be automatically repaired.

If Automatic, tolerance is calculated based on the input features and addresses only extremely small variations. The value is written to the log file.

See Tolerance above, as well as Geometry Concepts > Tolerance.

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.

Z and Measures Parameters

Connect Z Mode

If applicable, select a method for handling z values.

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.

Measures/Z Conflict Value

Select a method for handling 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: Missing values are assigned this 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.

Outside Tolerance Parameters

Fill All Gaps

Select an option for gaps repair:

Yes: All gaps in the coverage will be filled.
No: Only gaps within the tolerance will be filled.

Repair Method

Select a method for repairing gaps and overlaps that are larger than the Tolerance value.

Longest Boundary	The area with the longest boundary absorbs overlaps and gaps.
Random	Areas are chosen at random to absorb overlaps and gaps.
Priority (Edge Preserving)	Areas designated higher priority absorb overlaps. Areas with lower priority are expanded to cover gaps. Higher priority areas have their boundaries preserved.
Priority (Area Englarging)	Areas designated higher priority absorb overlaps and gaps. Higher priority areas may be enlarged to cover gaps.

Priority Attribute

When Repair Method is either Priority (Edge Preserving) or Priority (Area Englarging), specify the attribute containing the priority value.

Priority values are positive integers.

Zero (0) denotes the highest priority.

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
Aliases	SliverRemover
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.