Populate featureTable with centroid only geometry from feature service

[ForrestKaye]

Hello,

    I was wondering if it is possible to populate a FeatureTable from a Feature Service with the centroid only geometry.  Looking through the documentation and attempting this does not make it seem possible with the maps SDK.  I could do it by pinging the FeatureService directly and using the returnCentroid parameter but that does not seem to be exposed in the SDK.

    If this is not possible can I put an enhancement request in for it?  Use case is this: Querying polygon features hosted in a service. I do not want to return the entire geometry for performance reasons. I want to sort the features by nearest location to the user.  Having access to the centroid would satisfy my sorting and performance needs.  

[Ting]

Hi Forrest, thanks for posting. You are right, currently our SDK doesn't support the returnCentroid parameter.

Some (SDK-client-side) alternatives that may be worth a try: GeometryEngine.labelPoint(for:), or Envelope.center, for a rough estimate if the polygon is simple.

As they may not be suitable for your use case, please feel free to post in Native SDKs Ideas with your use case.

[ForrestKaye · Accepted solution]

Hi Ting,

So for my intended workflow those will not work for me as I am populating my feature table with null geometries (queryParameters.returnGeometry = false) So will not have any geometry to get either the label point or the envelop center. 

At first I had thought that some bare bones spatial data (label point or envelop center) did come through on the query even if the returnGeometry = null. But that does not seem to be the case. 

My Hope was that I could get a minimal about of spatial data on my polygon so I can then sort them via distance to my users.  This would keep my queries performant as the geometries are quite complex and also avoid errors I had seen on the service alerting me too many queries had been performed querying complex geometries and would need to wait 60 seconds before performing more queries.  

[Ting]

Thanks for explaining your use case. I agree that not to fetch the complex geometry is a big time saver. Unfortunately, we haven't quite matched up with all the parameters that the REST API provides yet.

So if you want this feature, a few options to consider:

• Create a feature request in Native SDKs Ideas board with your use case. Thus, this feature request can be triaged by our PMs.
• Maybe include a pre-computed field in the feature table for the centroid, if you have control over that feature table.
• Make a raw URLRequest to the REST API endpoint, and parse the response as you need. The URL structure for the GET request is relatively straightforward: https://YOUR_FEATURE_SERVER/FeatureServer/0/query?f=json&outFields=OBJECTID,STATE_NAME&where=1%3D1&o... 
  • simply swap the feature server and API key from the URL
  • or create the request in Swift such as

let baseURL = URL(string: "https://…/FeatureServer/0/query")!
var components = URLComponents(url: baseURL, resolvingAgainstBaseURL: false)!
components.queryItems = [
    URLQueryItem(name: "f", value: "json"),
    URLQueryItem(name: "outFields", value: "OBJECTID,STATE_NAME"),
    URLQueryItem(name: "where", value: "1=1"),
    URLQueryItem(name: "outSR", value: "4326"),
    URLQueryItem(name: "returnDistinctValues", value: "false"),
    URLQueryItem(name: "returnGeometry", value: "false"),
    URLQueryItem(name: "returnM", value: "false"),
    URLQueryItem(name: "returnZ", value: "false"),
    URLQueryItem(name: "returnCentroid", value: "true"),
    URLQueryItem(name: "token", value: "YOUR_API_KEY")
]
guard let finalURL = components.url else {
    fatalError("Invalid URL components")
}
var request = URLRequest(url: finalURL)
request.httpMethod = "GET"

• It is possible to use DataTaskInterceptor to intercept the query response and get the centroids from there, but I don't recommend doing that to introduce some fragile code logics. Nonetheless, I sent you a DM with a code snippet in case you want to give it a try.

[ForrestKaye]

Thank you for the detailed and thorough response.  I'm not quite sure the route we'll go but I think you pretty much covered all options there.  Thank you.  I will be putting in a request for that via in the native SDK's Ideas.

Cheers!