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How to calculate the geographic distance between two points with ksqlDB

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How to calculate the geographic distance between two points with ksqlDB

You can use the ksqlDB GEO_DISTANCE function to calculate the distance between two latitude and longitude points.

Setup

You have a topic that contains longitude and latitude data. For our example, let's say it contains information for phone repair shops:

CREATE TABLE repair_center_table (repair_state VARCHAR PRIMARY KEY, long DOUBLE, lat DOUBLE)
       WITH (KAFKA_TOPIC='repair_center',
             PARTITIONS=1,
             VALUE_FORMAT='AVRO');

Now you also have a topic that contains insurance claim event data for people who have lost or damaged an insured phone:

CREATE STREAM insurance_event_stream (customer_name VARCHAR, phone_model VARCHAR, event VARCHAR,
                                      state VARCHAR, long DOUBLE, lat DOUBLE)
       WITH (KAFKA_TOPIC='phone_event_raw',
             PARTITIONS=1,
             VALUE_FORMAT='AVRO');

The goal is to route customers to the nearest repair shop. In order to calculate how far away the repair center is from the insurance event, we will need to create a stream that joins the insurance events with our repair center reference data. or this use case, let’s assume there is only one repair center in each STATE and the repair center in an event’s STATE is the closest repair center.

CREATE STREAM insurance_event_with_repair_info AS
SELECT * FROM insurance_event_stream iev
INNER JOIN repair_center_table rct ON iev.state = rct.repair_state
EMIT CHANGES;

Now you have a stream that contains the lat-long of the repair shop and the phone damage event lat-long.

The last step is to convert the two sets of lat-long coordinates to a distance:

SELECT iev_customer_name,
    iev_state,
    GEO_DISTANCE(iev_lat, iev_long, rct_lat, rct_long, 'miles') AS dist_to_repairer_km
FROM insurance_event_with_repair_info
EMIT CHANGES;

The GEO_DISTANCE function calculates the great-circle distance between two lat-long points, both specified in decimal degrees. An optional final parameter specifies km (the default) or miles.

Running the example

You can run the example backing this tutorial in one of two ways: locally with the ksql CLI against Kafka and ksqlDB running in Docker, or with Confluent Cloud.

Local With Docker

Prerequisites

Run the commands

Clone the confluentinc/tutorials GitHub repository (if you haven't already) and navigate to the tutorials directory:

git clone git@github.com:confluentinc/tutorials.git
cd tutorials

Start ksqlDB and Kafka:

docker compose -f ./docker/docker-compose-ksqldb.yml up -d

Next, open the ksqlDB CLI:

docker exec -it ksqldb-cli ksql http://ksqldb-server:8088

Run the following SQL statements to create the repair_center_table table and insurance_event_stream stream backed by Kafka running in Docker and populate them with test data.

CREATE TABLE repair_center_table (repair_state VARCHAR PRIMARY KEY, long DOUBLE, lat DOUBLE)
       WITH (KAFKA_TOPIC='repair_center',
             PARTITIONS=1,
             VALUE_FORMAT='AVRO');
INSERT INTO repair_center_table (repair_state, long, lat) VALUES ('NSW', 151.1169, -33.863);
INSERT INTO repair_center_table (repair_state, long, lat) VALUES ('VIC', 145.1549, -37.9389);
CREATE STREAM insurance_event_stream (customer_name VARCHAR, phone_model VARCHAR, event VARCHAR,
                                      state VARCHAR, long DOUBLE, lat DOUBLE)
       WITH (KAFKA_TOPIC='phone_event_raw',
             PARTITIONS=1,
             VALUE_FORMAT='AVRO');
INSERT INTO insurance_event_stream (customer_name, phone_model, event, state, long, lat)
    VALUES ('Lindsey', 'iPhone 11 Pro', 'dropped', 'NSW', 151.25664, -33.85995);
INSERT INTO insurance_event_stream (customer_name, phone_model, event, state, long, lat)
    VALUES ('Debbie', 'Samsung Note 20', 'water', 'NSW', 151.24504, -33.89640);

Next, create a stream that joins the insurance events with our repair center reference data. Note that we first tell ksqlDB to consume from the beginning of the insurance_event_stream stream.

SET 'auto.offset.reset'='earliest';
  
CREATE STREAM insurance_event_with_repair_info AS
  SELECT * FROM insurance_event_stream iev
  INNER JOIN repair_center_table rct
  ON iev.state = rct.repair_state
  EMIT CHANGES;

Finally, convert the two sets of lat-long coordinates to a distance:

SELECT iev_customer_name,
    iev_state,
    GEO_DISTANCE(iev_lat, iev_long, rct_lat, rct_long, 'miles') AS dist_to_repairer_km
FROM insurance_event_with_repair_info
EMIT CHANGES;

The query output should look like this:

+-----------------------------+-----------------------------+-----------------------------+
|IEV_CUSTOMER_NAME            |IEV_STATE                    |DIST_TO_REPAIRER_KM          |
+-----------------------------+-----------------------------+-----------------------------+
|Lindsey                      |NSW                          |8.020734621148486            |
|Debbie                       |NSW                          |7.704588172240076            |
Query Completed

When you are finished, exit the ksqlDB CLI by entering CTRL-D and clean up the containers used for this tutorial by running:

docker compose -f ./docker/docker-compose-ksqldb.yml down
Confluent Cloud

Prerequisites

Create Confluent Cloud resources

Login to your Confluent Cloud account:

confluent login --prompt --save

Install a CLI plugin that will streamline the creation of resources in Confluent Cloud:

confluent plugin install confluent-cloud_kickstart

Run the following command to create a Confluent Cloud environment and Kafka cluster. This will create resources in AWS region us-west-2 by default, but you may override these choices by passing the --cloud argument with a value of aws, gcp, or azure, and the --region argument that is one of the cloud provider's supported regions, which you can list by running confluent kafka region list --cloud <CLOUD PROVIDER>

confluent cloud-kickstart --name ksqldb-tutorial \
  --environment-name ksqldb-tutorial \
  --output-format stdout

Now, create a ksqlDB cluster by first getting your user ID of the form u-123456 when you run this command:

confluent iam user list

And then create a ksqlDB cluster called ksqldb-tutorial with access linked to your user account:

confluent ksql cluster create ksqldb-tutorial \
  --credential-identity <USER ID>

Run the commands

Login to the Confluent Cloud Console. Select Environments in the lefthand navigation, and then click the ksqldb-tutorial environment tile. Click the ksqldb-tutorial Kafka cluster tile, and then select ksqlDB in the lefthand navigation.

The cluster may take a few minutes to be provisioned. Once its status is Up, click the cluster name and scroll down to the editor.

In the query properties section at the bottom, change the value for auto.offset.reset to Earliest so that ksqlDB will consume from the beginning of the streams we create.

Enter the following statements in the editor and click Run query. This creates the repair_center_table table and insurance_event_stream stream and populates them with test data.

CREATE TABLE repair_center_table (repair_state VARCHAR PRIMARY KEY, long DOUBLE, lat DOUBLE)
       WITH (KAFKA_TOPIC='repair_center',
             PARTITIONS=1,
             VALUE_FORMAT='AVRO');

INSERT INTO repair_center_table (repair_state, long, lat) VALUES ('NSW', 151.1169, -33.863);
INSERT INTO repair_center_table (repair_state, long, lat) VALUES ('VIC', 145.1549, -37.9389);

CREATE STREAM insurance_event_stream (customer_name VARCHAR, phone_model VARCHAR, event VARCHAR,
                                      state VARCHAR, long DOUBLE, lat DOUBLE)
       WITH (KAFKA_TOPIC='phone_event_raw',
             PARTITIONS=1,
             VALUE_FORMAT='AVRO');

INSERT INTO insurance_event_stream (customer_name, phone_model, event, state, long, lat)
    VALUES ('Lindsey', 'iPhone 11 Pro', 'dropped', 'NSW', 151.25664, -33.85995);
INSERT INTO insurance_event_stream (customer_name, phone_model, event, state, long, lat)
    VALUES ('Debbie', 'Samsung Note 20', 'water', 'NSW', 151.24504, -33.89640);

Next, create a stream that joins the insurance events with our repair center reference data. Paste in the following query and click Run query.

CREATE STREAM insurance_event_with_repair_info AS
  SELECT * FROM insurance_event_stream iev
  INNER JOIN repair_center_table rct
  ON iev.state = rct.repair_state
  EMIT CHANGES;

Finally, convert the two sets of lat-long coordinates to a distance:

SELECT iev_customer_name,
    iev_state,
    GEO_DISTANCE(iev_lat, iev_long, rct_lat, rct_long, 'miles') AS dist_to_repairer_km
FROM insurance_event_with_repair_info
EMIT CHANGES;

The query output should look like this:

+-----------------------------+-----------------------------+-----------------------------+
|IEV_CUSTOMER_NAME            |IEV_STATE                    |DIST_TO_REPAIRER_KM          |
+-----------------------------+-----------------------------+-----------------------------+
|Lindsey                      |NSW                          |8.020734621148486            |
|Debbie                       |NSW                          |7.704588172240076            |
+-----------------------------+-----------------------------+-----------------------------+

Clean up

When you are finished, delete the ksqldb-tutorial environment by first getting the environment ID of the form env-123456 corresponding to it:

confluent environment list

Delete the environment, including all resources created for this tutorial:

confluent environment delete <ENVIRONMENT ID>