The Feature Layer feed type in ArcGIS Velocity polls an ArcGIS Online or ArcGIS Server feature layer for features.
Examples
The following are example uses of the Feature Layer feed:
- A user configures a feed referencing an ArcGIS Server hosted feature layer to load features added by users.
- A GIS analyst provides the URL to an ArcGIS Server feature layer (such as https://sampleserver6.arcgisonline.com/arcgis/rest/services/Wildfire/FeatureServer/2) containing the desired features to load every minute, for use in a real-time analytic.
Usage notes
Keep the following in mind when using the Feature Layer feed:
- The feed will poll the feature layer to load features at the rate defined on the Feed Polling Interval step of the feed configuration wizard.
- If a timestamp field value is not specified, at every interval the feature layer feed will load all features from the feature layer as events to be processed.
- If a timestamp field value is specified, the first time Velocity polls the feature layer it will load all features with a timestamp field datetime within the past minute and less than the first feed poll time that also meet the criteria of the WHERE clause. Each subsequent poll, only features with a timestamp field value between the last polling time and the current polling time that also meet the criteria of the WHERE clause will be loaded.
- When browsing to select a feature layer item, you can filter by your folders, favorites, groups, organization, or all of ArcGIS Online. You can then further filter by date modified, date created, and tags.
- ArcGIS Server feature layers can also be loaded using a URL. This should be an ArcGIS Server services directory REST URL (such as https://sampleserver6.arcgisonline.com/arcgis/rest/services/Wildfire/FeatureServer/2). This URL should end in /FeatureServer/# or /MapServer/#, where # is the layer number.
- To load a secured feature layer from a URL, you must first add a service or document from URL to ArcGIS Online and choose to store credentials. You can then browse to the registered ArcGIS Online item to select the secured feature layer.
- The feature layer must be accessible over the internet.
- When a polling frequency is set, the polling occurs on regular clock intervals as opposed to the start time of the feed. For example, if a feed is set to poll for data every 5 minutes, and the feed is started at 8:03 a.m., the first request for data will occur at 8:05 a.m., the next at 8:10 a.m., and so on.
- Use caution when defining the feed polling interval. It is essential to ensure that the feature layer that you are polling is capable of returning responses within the polling interval specified. A best practice is to test the response time of a query request to this feature layer, using the same query that you apply in the feed configuration. The polling interval should never be set to a shorter interval than the typical response time of your feature layer query. For more information on scheduling feed polling intervals, see Feed polling interval scheduling.
- After configuring the feature layer connection parameters, see Configure input data to learn how to define the schema and the key parameters.
Parameters
The following are parameters for the Feature Layer feed:
| Parameter | Explanation | Data type |
|---|---|---|
WHERE clause | Specifies a WHERE clause to filter features loaded from the specified feature layer. The default is to load all features using 1=1. This default WHERE clause can be modified to include specific attribute values and logic conditions. SQL 92 WHERE clause syntax on the fields in the layer is supported for most feature layers. Feature layers generated by Velocity or feature layers in ArcGIS Enterprise running on a spatiotemporal data source have restrictions on what is supported; they only support a subset of SQL 92. Below is a list of supported SQL 92 with such feature layers:
| QueryString |
Out fields | Specifies which fields from the feature layer should be loaded into Velocity. The default value is an asterisk (*), which denotes that all fields will be loaded. If specifying specific fields, this should be specified with comma separated field names, for example: OBJECTID,device_id,timestamp,horizontal_accuracy,latitude,longitude | String |
Output spatial reference | Specifies the well-known ID (WKID) of a spatial reference. The default WKID is 4326. Velocity will load data from the feature layer in the spatial reference set in this parameter. | String |
Timestamp field | Specifies a date field for retrieving only the latest features. If a timestamp field value is not specified, at every interval the feed will load all features from the feature layer as events to be processed. If a timestamp field value is specified, the first time Velocity polls the feature layer it will load all features with a timestamp field datetime within the past minute and less than the first feed poll time that also meets the criteria of the WHERE clause. Each subsequent poll, only features with a timestamp field value between the last polling time and the current polling time that also meet the criteria of the WHERE clause will be loaded. | String |
Considerations and limitations
There are several considerations and limitations to keep in mind when using the Feature Layer feed:
- The feature layer must be accessible over the internet.
- The polling interval should never be set to a shorter interval than the typical response time of your feature layer query. For more information on scheduling feed polling intervals, see Feed polling interval scheduling.
- Velocity does not support layers that require credits for data queries.