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:
- Redirect non-polygonal geometries onto the Invalid port.
- Dissolve the input polygonal geometries to remove shared boundaries and overlapping regions.
- Densify the dissolved polygonal geometries.
- Determine the convex hull of the densified polygonal geometries.
- Overlay the convex hull against the densified polygonal geometries to compute empty regions between the polygonal geometries.
- Triangulate the empty regions. Keep only triangles that are sufficiently short in length – those that satisfy the Maximum Triangle Length parameter.
- Dissolve the triangles to form connectors.
- For each connector, check to see if it is valid. It is valid if it shares a boundary with a dissolved polygonal geometry.
- Output all features not touched by any connectors to the Untouched port.
- Dissolve valid connectors with dissolved polygonal geometries to form amalgams.
- For each amalgam, remove small holes that do not satisfy the Minimum Hole Area parameter. Remaining (large) holes are output to the Holes port.
- For each amalgam, find all triangles that formed a part of its connectors. Output these triangles to the Triangles port.
- Output all amalgams to the Amalgamated port.
- For attribute behavior, please see List Name and ID Attribute in the Parameters section.
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.
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.
Parallel Processing Levels
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 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.
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.
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:
- Self Amalgamation: This mode amalgamates a polygonal geometry against itself. It would handle the two peninsulas case, but not the two neighboring islands case.
- Binary Amalgamation (default): This mode amalgamates different polygonal geometries. It would handle the two neighboring islands case, but not the two peninsulas case.
- Self, Binary Amalgamation: This mode combines the Self Amalgamation and the Binary Amalgamation. It would handle both the two peninsulas case and the two neighboring islands case.
Self, Binary Amalgamation
This parameter controls whether input polygonal features are dissolved up front. The default value is Yes.
- Yes: This value dissolves input polygonal features. The AreaAmalgamator was designed with the assumption that input features do not overlap. This value enforces that assumption. Dissolving input up front also remedies input polygonal features that may not be overlapping, but whose shared boundaries become overlapping after the densification step due to limited precision. The overlapping due to limited precision could reduce the performance of the AreaAmalgamator.
- No: This value is meant for advanced users who want finer control of the AreaAmalgamator. Some users would rather not dissolve the input to improve performance because in some cases, not dissolving the input will not cause undesirable side effects.
Dissolve Input: Yes
Amalgamation Mode: Binary
Dissolve Input: No
Amalgamation Mode: Binary
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.|
Dissolve Input: Yes
Amalgamation Mode: Self
Dissolve Input: No
Amalgamation Mode: Self
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.
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 multiple input features dissolve into a single feature, then only one set of feature attributes are kept on the dissolved feature.
- If two input geometries share a boundary – for example, two peninsulas glued together – the user might expect triangle connectors to form between the two geometries when the Binary Amalgamation mode is selected. However, such geometries will first be dissolved, making it much more likely that Binary Amalgamation will not cause triangle connectors to form between the peninsulas. To overcome this issue, please select the Self, Binary Amalgamation mode.
If the Maximum Triangle Length specified is less than Maximum Triangle Width, the results may be unpredictable.
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.
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Tags Keywords: Amalgamator