Send notification to Android devices in radius using Azure Notification Hub

I am prototyping using Azure Functions and Notification Hub.

As part of my function, I want to select a set of devices based on a geospatial query and send a notification to these listed devices.

I have notifications working with Firebase and Android, but how do I set up a target device group based on the query result?

#r "Microsoft.Azure.NotificationHubs"
#load "location.csx"


using System;
using System.Net;
using Microsoft.Azure.NotificationHubs;


public static async Task Run(LocationInfo message, IAsyncCollector<Notification> notification, TraceWriter log)
{
    log.Info($"Sending GCM notification of a new user");
    string gcmNotificationPayload = "{\"data\": {\"message\": \"test message")\" }}";
    log.Info($"{gcmNotificationPayload}");
    await notification.AddAsync(new GcmNotification(gcmNotificationPayload));
}