Symmetric Difference Creator Processor

The Symmetric Difference Creator Processor is used to clip or remove the intersecting portion of an event record’s geometry and a geofence from the union of the two geometries. The symmetric difference of two geometries is essentially an exclusive OR statement.

Example

Use the Symmetric Difference Creator Processor to union and clip the intersection of a tornado and a zone of interest. As the tornado travels through the zone, the areas directly impacted can be clipped and removed from the zone. The remaining parts of the zone can be used to show areas not directly impacted by the tornado.

Usage notes

Keep the following in mind when working with the Symmetric Difference Creator Processor:

• The Symmetric Difference Creator Processor requires two discrete geometries be specified. For example, a regular expression cannot be used to specify several different geofences to obtain a symmetric difference for the collection of geometries.
• The processor requires geometries have the same type. For example, the symmetric difference between a point and a polyline as a union of the two cannot be computed.
• The processor requires the field containing the event record’s geometry be specified. A geometry field's name can be specified or a field tagged with the GEOMETRY tag in a GeoEvent Definition can be used to identify the geometry field.
• The Geometry Field parameter displays the name of every field from every GeoEvent Definition with a geometry data type. When selecting the geometry field by name, choose the name of the correct geometry field that corresponds to the event record’s GeoEvent Definition.
• The processor can be configured to replace the event record's geometry with the computed symmetric difference or place the symmetric difference geometry into a new geometry field using the Replace Geometry parameter. Adding a new field to an event record alters the event record's schema, which requires GeoEvent Server to create a new GeoEvent Definition. The new GeoEvent Definition will be managed by GeoEvent Server and deleted if changes are made to the processor or the GeoEvent Service in which the processor is used.
• Choosing Yes for the Tag the New Geometry Field as Geometry parameter explicitly tells GeoEvent Server which geometry field should be treated as the event record’s realized geometry for subsequent processing or output.

Parameters

The following are the parameters for the Symmetric Difference Creator Processor:

Parameter	Description
Name	A descriptive name for the processor used for reference in GeoEvent Manager.
Processor	Specifies the processor selected.
Geometry Field	The name of the geometry field or the field tagged with the GEOMETRY tag from the inbound event record the processor uses to calculate the symmetric difference with an intersecting geofence.
Replace Geometry	Specifies whether to replace the current event record geometry with the symmetric difference of the event record and geofence geometries. The default is Yes. Yes—The event record geometry is replaced with the geometry of the symmetric difference. No—The event record geometry is not replaced. The geometry of the symmetric difference will be stored in a new geometry field as part of the event record. Altering an event record’s schema by adding a new field name requires a new GeoEvent Definition.
New Geometry Field Name (Conditional)	The name of the new geometry field where the geometry of the calculated symmetric difference is stored. The parameter is shown when Replace Geometry is set to No and is hidden when set to Yes.
Tag the New Geometry Field as Geometry (Conditional)	Specifies whether the new geometry field created by the processor is tagged with the GEOMETRY tag. The GEOMETRY tag is used by GeoEvent Server to identify the event record’s realized geometry when multiple geometry fields are present. The default is No. The parameter is shown when Replace Geometry is set to No and is hidden when set to Yes.
New GeoEvent Definition Name (Conditional)	The name assigned to the new GeoEvent Definition. The new GeoEvent Definition will combine the schema of the inbound event record with the new geometry field. The parameter is shown when Replace Geometry is set to No and is hidden when set to Yes.
Geofence	The category and name of the geofence. The processor uses the geofence to calculate the symmetric difference with the geometry of the intersecting event record. The resulting geometry is the union of the event record and geofence geometries with the intersecting portion clipped (or removed). The required format for specifying a geofence is category/name, for example: Hurricanes/Doe AVL/Vehicle1

Considerations and limitations

Consider replacing the existing event record geometry with the geometry representing the symmetric difference prior to sending the event data to a feature service. Feature services only support one geometry type field, and therefore, whichever field is not tagged with the GEOMETRY tag will be converted and kept as a string.