AreaAmalgamator

Generalizes area geometry by connecting and combining neighboring features and/or filling in holes and details.

Typical Uses

Reducing complexity
Creating amalgamated features for labeling
Optimizing geometry for different scales

How does it work?

The AreaAmalgamator receives features with area geometry and generalizes them, reducing complexity and connecting nearby features.

Areas can be amalgamated with other areas, with themselves (generalizing irregularly shaped areas), or both. Features are generally dissolved before processing, which may be overridden.

Connections are created by triangulating within the possible connecting space (the interior of a convex hull) and using those triangles to build connecting geometry. Triangles are controlled by two parameters:

Maximum Triangle Width controls the density of triangles created along feature boundaries, affecting the level of detail versus coarseness of the connecting geometry. Width is measured on the side of the triangle that lies along the feature boundary.
- A maximum width that is less than the distance between coordinates on the feature will increase the number of triangles, which may produce finer detail in some cases but may increase processing time.
- A maximum width that is greater than the distance between coordinates will have no effect.
Maximum Triangle Length: Controls which triangles are kept to create connecting geometry, which determines whether or not features are connected based on their proximity. Length is measured on the longest side of the triangle.

Donut polygons are supported, and holes in the output amalgams may be kept or removed based on their area.

Unique IDs may be generated for amalgams which also identify related holes and triangles. Attributes from input features may be accumulated into a list attribute.

Features that overlap or share boundaries are, by default, dissolved before amalgamation, which may be overridden. If Dissolve Input is No, any resulting overlapping areas will not be amalgamated. This may include areas that shared a boundary prior to triangulation.

Amalgamation Basics

Basic amalgamation is performed as follows.

Input	Area features are input.
Convex Hull	The convex hull containing all features is calculated.
Area to triangulate	The area within the hull but excluding the input features is determined.
Triangulate	This area is triangulated. The width of the triangles can be adjusted with the Maximum Triangle Width parameter. Width is the side that lies along the input feature’s boundary.
Connect	Triangle length is evaluated, and those under the Maximum Triangle Length parameter value are used to create connections. Length is the longest side of the triangle.
Output	Amalgamated and Untouched features are output.

Amalgamation Modes

Features may be amalgamated with themselves, each other, or both.

Input features	Two islands are input. Note the inlets and level of detail along the coastlines.
Self Amalgamation	The features are only processed individually, and neighboring features are not connected. Connecting triangles fill in the long inlet on the upper island, and generalize the coastline of the lower one.
Binary Amalgamation	The features are processed against other features, but not themselves. The islands are connected together. The original inlets and coastline detail remain intact because self-amalgamation was not performed.
Self, Binary Amalgamation	Both types of amalgamation are done. Binary amalgamation connects the islands together, and self-amalgamation generalizes the coastline and fills in the long inlet.

Holes

Donut holes may be present in input features or produced during amalgamation.

In either case, Minimum Hole Area determines whether they are kept or dissolved. Holes smaller than the minimum value are dissolved.

Input features

This group of islands is to be amalgamated.The coordinate system is UTM, with ground units in meters.

Amalgamation Mode is Self, Binary Amalgamation.

Minimum Hole Area = 100000

Holes appear where the triangulation results exceed the specified Maximum Triangle Length of 1000 meters.

Holes of 100,000 square meters or larger are kept as donut holes in the amalgamated area.

The amalgam is output as a donut polygon, and the holes are output separately as individual polygons.

Amalgamated

Holes

Minimum Hole Area = 10000000

The minimum is greater than the area of any holes.

All holes are dissolved.

Amalgamated

Attributes

Attributes are removed from Amalgamated output features.

A list attribute may be created to retain attributes from all input features contributing to an amalgam, and unique IDs may be generated and added as an attribute.

Where features are dissolved (Dissolve Input > Yes), attributes values are retained from one of the dissolved features, which is arbitrarily selected. Dissolving is performed on both overlapping areas and areas with shared boundaries.

Untouched features keep their attributes.

Usage Notes

Dissolve Input can result in lost attribute values. Using a Dissolver prior to the AreaAmalgamator can provide finer control and list attribute generation.
If the Maximum Triangle Length specified is less than Maximum Triangle Width, the results may be unpredictable.

Creating and Modifying Area Features

These transformers work with polygons in a variety of ways.

Area Transformers Comparison

	Function	Transformer Description
AreaBuilder	Creating areas from topologically connected lines where they form closed shapes.	Creates polygons from topologically correct linear features.
LineCloser	Creating areas from individual linear features.	Converts a linear feature to an area by connecting the end point to the start point.
Dissolver	Combining 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	Calculating areas.	Calculates the planar or sloped area of polygon geometries and adds the results as attributes.
AreaGapAndOverlapCleaner	Cleaning up overlaps and gaps to create contiguous coverage.	Repairs area topologies by resolving gaps and overlaps between adjacent areas.
AreaAmalgamator	Generalizing areas.	Generalizes area geometry by connecting and combining neighboring features and/or filling in holes and details.
DonutBridgeBuilder	Converting donut areas to non-donut areas by connecting holes to the perimeter.	Builds connections between donut holes with the outer boundary of a donut, resulting in a polygon-equivalent representation of the input donut.
DonutBuilder	Converting areas within areas to donut holes.	Cuts holes in area features where they fully enclose another area, creating donut polygons.
DonutHoleExtractor	Separating donut areas into their parts.	Separates donut polygons into outer shell and hole polygons.
HoleCounter	Counting the number of holes in a donut area.	Adds a new attribute whose value is the number of holes in the feature. If the feature is not a polygonal feature, 0 will be returned.
AreaOnAreaOverlayer	Finding polygon overlaps and extracting 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	Finding 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	Identifying points that fall within polygons, and sharing 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

By specifying one or more Group By attributes, the input polygonal features will be partitioned into groups and the amalgamation process will be executed separately on each group. Within each group, all features will have the same values for the selected Group By attributes.

If no Group By attributes are selected, a single group will be formed containing all input polygonal features.

By default, no Group By attributes are selected.

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

Amalgamation Mode	Select a method for amalgamation: Self Amalgamation: Areas are amalgamated against themselves, generalizing details, and are not connected to other areas. Binary Amalgamation (default): Areas are amalgamated against other areas, connecting them where appropriate. Self, Binary Amalgamation: Areas are amalgamated against themselves and other areas, performing both tasks.
Dissolve Input	Select an option for dissolving areas prior to amalgamation: Yes (default): Dissolve overlapping areas and shared boundaries. No: Do not dissolve areas. Overlapping areas will not be amalgamated.
Maximum Triangle Width	Specify the maximum width for triangles, in ground units. Width is measured on the side of the triangle that lies along the feature boundary. This value will increase the number of triangles if it is less than the distance between nodes on the feature.
Maximum Triangle Length	Specify the maximum length of triangles to be used to create connectors. Length is determined by the longest side of the triangle, regardless of its position relative to the feature boundary. Longer triangles are discarded.
Minimum Hole Area	Specify the minimum size that areas must be, in square ground units, to be kept and create donut holes in the amalgam. Smaller holes are dissolved into the amalgam.
ID Attribute (optional)	(Optional) Name the attribute to contain a generated unique ID for each amalgam and its related triangles and holes. Untouched features have the attribute added but the values will be empty.

Generate List

When enabled, adds a list attribute to the output amalgams.

List Name

Enter a List Name to be created on each output feature, containing an element for each input feature which contributed to that geometry.

This parameter can also be used to preserve attributes from input features.

Note List attributes are not accessible from the output schema in FME 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 List

All Attributes: Every attribute from all input features that created an output feature will be added to the list specified in List Name.

Selected Attributes: Only the attributes specified in the Selected Attributes parameter will be added to the list specified in List Name.

Selected Attributes

The attributes to be added to the list when Add To List is Selected Attributes.

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	None
Aliases	Amalgamator
History

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