Difference Creator Processor

The Difference Creator Processor can be used to determine the intersection between an event record’s geometry and a single geofence. The processor clips or removes the portion of the geofence that intersects the event record’s geometry.

Examples

The following are example uses of the Difference Creator Processor:

• Calculating the geometric difference between a geofence and an intersecting event record can show areas snow has been cleared by snowplows and areas where snow remains.
• Calculating the geometric difference between a geofence and an intersecting event record can show areas that have been searched by a field crew and areas that still need to be searched.
• Calculating the geometric difference between a geofence and an intersecting event record can aid with monitoring whether assets have touched, entered, or intersected a fixed boundary.

Usage notes

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

• The Difference Creator Processor requires two discrete geometries be specified. You cannot, for example, use a regular expression to specify several geofences and remove the intersecting portions of each geofence from the event record’s geometry.
• The processor also requires the dimensionality of the geofence be equal to or greater than that of the event record's geometry. You cannot, for example, clip or subtract a point from a polyline or a polyline from a polygon.
• The processor requires the field containing the event record’s geometry be specified. A geometry field name can be specified, or the GEOMETRY tag can be applied to a field in a GeoEvent Definition to identify the geometry field.
• The Geometry Field parameter will show the name of every field from every GeoEvent Definition containing a data type of geometry. 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 difference of the two geometries or it can place the difference into a new geometry field using the Replace Geometry parameter. Altering an event record's schema by adding a new field 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 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 GEOMETRY tagged field from the inbound event record that the processor uses to calculate the geometric difference with an intersecting geofence.
Replace Geometry	Specifies whether to replace the current event record geometry with the geometry of the clipped geofence. The default is Yes. Yes—The event record geometry will be replaced with the geometry of the clipped geofence. No—The event record geometry will remain the same. The geometry of the clipped geofence is 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 clipped geofence geometry will be 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)	Determines whether the new geometry field created by the processor will be tagged as GEOMETRY. 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 additional 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 registered with GeoEvent Server. The processor uses the geofence to calculate the geometric difference with an intersecting event record. The resulting geometry is the clipped portion of the geofence. The required format is category/name, specified as a pair of regular expression patterns. For example, Pavilions/Alpha uses the geofence Alpha in the category Pavilions with the event record geometry. Note: Multiple geofence category/name expressions cannot be specified as a comma separated list. For example, specifying Countries/France, Countries/Germany cannot be used to specify the geofences France or Germany. Note: Regular expressions are used for both the category and the name. Because the expression .*/.* includes all geofences in all categories, and this processor only works with two geofences, this pattern is unlikely to be used. Remember, regular expression pattern matches are case-sensitive.

Considerations and limitations

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