The AreaAmalgamator accepts polygonal geometries – including donuts – as input, and produces triangles that join input features into connected pieces, or amalgams. Small holes are removed at the end of this process.
The strategy for generalizing polygonal geometries is as follows:
Polygonal geometries, including donuts. The polygonal geometries may overlap and share boundaries. However, each geometry should be valid (that is, not self-intersecting or non-planar).
Amalgams computed from input polygonal geometries.
Input polygonal geometries that are not touched by valid triangle connectors.
Holes in the amalgams whose areas exceed the Minimum Hole Area parameter.
Triangles that form the valid connectors joining input polygonal geometries.
Non-polygonal input. Occasionally, if an unexpected condition is met, some invalid intermediate results will be posted to this port.
Input | Output |
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Triangles (red) |
|
Amalgamated (green) |
|
Holes (black) |
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.
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.
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.
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 on 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.
This parameter controls the mode of amalgamation. The AreaAmalgamator is conceptually a binary operator that causes two nearby geometrical details to connect together. However, two geometrical details may be on the same geometry. Imagine two peninsulas protruding from the same coast line, or two different geometries, such as two neighboring islands. Therefore, a number of options are provided here to accommodate the two conceptual models:
Input | Output: Amalgamated |
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Self Amalgamation |
|
Binary Amalgamation |
|
Self, Binary Amalgamation |
This parameter controls whether input polygonal features are dissolved up front. The default value is Yes.
Overlapping Input |
Dissolve Input: Yes Amalgamation Mode: Binary |
Dissolve Input: No Amalgamation Mode: Binary |
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Explanation |
The input dissolves into one polygon, thus the Binary mode causes the one polygon not to amalgamate. |
The input is not dissolved, thus the Binary mode causes the two input features to amalgamate, but because overlapping features were not dissolved, a hole results in the middle of the amalgam. |
Overlapping Input |
Dissolve Input: Yes Amalgamation Mode: Self |
Dissolve Input: No Amalgamation Mode: Self |
---|---|---|
Explanation |
The input dissolves into one polygon, thus the Self mode causes the one polygon to amalgamate. |
The input is not dissolved, thus the Self mode causes the two input features not to amalgamate. |
This parameter controls the widths of triangles that form the connectors. The width of the triangle is the width of its base, which is incident on the boundary of an input polygonal geometry (see figure below). The larger its value, the wider the triangles will be.
In terms of triangle count, decreasing this value generally increases (and will not decrease) the number of triangles generated. In terms of performance, having this value set too low could cause significant slowdowns. In terms of the appearance of the triangle connectors, having this value set too high could result in coarse looking connectors that appear skewed in shape.
Note: Tip: set the value of this parameter as high as possible, given that the amalgamated output still looks good to the eye.
More rigorously, after the input polygonal geometries are dissolved, extra vertices are added through a densification process. The densification interval controls the widths of triangles created. This parameter specifies the length of the densification interval.
This parameter controls the lengths of triangles that form the connectors. The length of the triangle is defined by the length of its longest side (see figure below). This value should not be less than the Maximum Triangle Width. The larger its value, the farther apart two input polygons can be and still be connected together by triangles in the formation of amalgams.
In terms of triangle count, decreasing this value generally decreases (and will not increase) the number of triangles generated. Changes in this value are not expected to have a significant impact on performance. In terms of the appearance of the triangle connectors, having this value set too high could result in the input polygons being output as a single amalgam.
This parameter controls which holes should be eliminated from the amalgams. The larger its value, the larger the remaining holes will be. In terms of hole count, decreasing this value generally increases (and will not decrease) the number of holes remaining in the amalgams.
This parameter specifies the name of a list attribute for the amalgams. For each amalgam, this list will contain an entry for each input feature whose polygonal geometry shares a boundary with the amalgam. All attributes from the input feature are recorded in the list entry, except feature level attributes prefixed by fme_.
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.
This parameter specifies the name of a unique identifier for the amalgams. If specified, each amalgam will receive an ID value that is unique across groups. All triangles and holes contained in an amalgam will receive the same ID as that amalgam.
Dissolving the input is necessary to remove shared boundaries and overlapping regions, with which the AreaAmalgamator cannot be expected to function properly. However, dissolving the input has some side effects:
If the Maximum Triangle Length specified is less than Maximum Triangle Width, the results may be unpredictable.
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.
Search for samples and information about this transformer on the FME Knowledge Center.
Associated FME function or factory: AmalgamatorFactory
Tags Keywords: Amalgamator