Displacer
Solves proximity conflicts between features using a variant of the Nickerson displacement algorithm. This transformer is usually used aftergeneralization.
Input and Output Ports
The features routed into the transformer through theBaseport are geometrically frozen (cannot move).
The features routed in through theCandidate港口比较反对Basefeature(s), displaced as necessary, and exit through theDisplacedport. If no displacement occurred, they exit through theUntouchedport.
Each comparison/displacement is independent of the others.
Basefeatures with geometries other than point, curve or area (polygon or ellipse or donut) will exit through theInvalidBaseport. Candidate features with geometries other than point, curve or simple area (polygon or ellipse) will exit through theInvalidCandidateport.
TheExtraBaseport holds extraBasefeatures as described in the Base Type parameter below.
Parameters
Transformer
You can use this option to narrow down which candidate features to compare with which base features.
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 usingProcess 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 aSQL ORDER BYstatement) 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 aGroup Byvalue need to arrive before any features (of any feature type or dataset) belonging to the next group. In this case, usingGroup BywithProcess 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.
Parameters
Specifies how much the displacement at one point in the candidate feature's geometry should affect the neighboring points. A lower value means that the candidate geometry can be deformed easily, while a higher value means that it will try its best to keep its original shape.
The Minimum Separating Distance parameter specifies the minimum separating distance between the candidate feature's geometry and the base feature's geometry after displacement.
The Displace Endpoints parameter specifies whether or not to displace the endpoints of candidate features whose geometries are unclosed lines.
The Base Type parameter specifies whether only a singleBasefeature will be used, or whether allBasefeatures will be used. If Bases First is selected, then the transformer assumes that allBasefeatures will enter the transformer before anyCandidatefeatures. Any furtherBasefeatures that arrive after the firstCandidatewill be output through theExtraBaseport. The same goes for anyBasefeatures after the first when in Single Base mode.
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, clickbeside the applicable parameter. For more information, seeTransformer Parameter Menu Options.
Transformer Categories
Related Transformers
FME Licensing Level
FME Professional edition and above
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Keywords: displacement resolve conflict generalization Nickerson generalize NickersonDisplacer