Add tools to implement asset monitoring telemetry

2025-08-04 13:17:50 +02:00 · 2025-03-13 22:43:29 +01:00
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+# Asset telemetry monitoring
+
+[!CAUTION]
+This is a PoC, not suitable for real world due to lack of any authentication and security
+
+## Pre-requisites
+
+- Python 3.12
+- Podman (or Docker)
+
+## Architecture
+
+The `dispatcher.py` script collects data (`cab` commands) from a CommandStation and sends it a MQTT broker. 
+
+The command being monitored is the `<l cab reg speedByte functMap>` one returned by the `<t cab speed dir>` throttle command. See the [DCC-EX command reference](https://dcc-ex.com/reference/software/command-summary-consolidated.html#t-cab-speed-dir-set-cab-loco-speed).
+
+`mosquitto` is the MQTT broker.
+
+The `handler.py` script subscribes to the MQTT broker and saves relevant data to the Timescale database.
+
+Data is finally save into a Timescale hypertable.
+
+## How to run
+
+### Deploy Timescale
+
+```bash
+$ podman run -d -p 5432:5432 -v $(pwd)/data:/var/lib/postgresql/data -e "POSTGRES_USER=dccmonitor" -e "POSTGRES_PASSWORD=dccmonitor" --name timescale timescale/timescaledb:latest-pg17
+```
+[!IMPORTANT]
+A volume should be created for persistent data
+
+Tables and hypertables are automatically created by the `handler.py` script
+
+### Deploy Mosquitto
+
+```bash
+$ podman run --userns=keep-id -d -p 1883:1883 -v $(pwd)/config/mosquitto.conf:/mosquitto/config/mosquitto.conf --name mosquitto eclipse-mosquitto:2.0
+```
+
+### Run the dispatcher and the handler
+
+```bash
+$ python dispatcher.py
+```
+
+```bash
+$ python handler.py
+```
+
+## Debug data in Timescale
+
+### Create a 10 secs aggregated data table
+
+```sql
+CREATE MATERIALIZED VIEW telemetry_10secs
+WITH (timescaledb.continuous) AS
+SELECT 
+    time_bucket('10 seconds', timestamp) AS bucket,
+    cab,
+    ROUND(CAST(AVG(speed) AS NUMERIC), 1) AS avg_speed,
+    MIN(speed) AS min_speed,
+    MAX(speed) AS max_speed
+FROM telemetry
+GROUP BY bucket, cab;
+```
+
+and set the update policy:
+
+```sql
+SELECT add_continuous_aggregate_policy(
+    'telemetry_10secs',
+    start_offset => INTERVAL '1 hour',  -- Go back 1 hour for updates
+    end_offset   => INTERVAL '1 minute', -- Keep the latest 5 min fresh
+    schedule_interval => INTERVAL '1 minute' -- Run every minute
+);
+
+```
+
+### Running statistics from 10 seconds table
+
+```sql
+WITH speed_durations AS (
+    SELECT 
+        cab,
+        avg_speed,
+        max_speed,
+        bucket AS start_time,
+        LEAD(bucket) OVER (
+            PARTITION BY cab ORDER BY bucket
+        ) AS end_time,
+        LEAD(bucket) OVER (PARTITION BY cab ORDER BY bucket) - bucket AS duration
+    FROM telemetry_10secs
+)
+SELECT * FROM speed_durations WHERE end_time IS NOT NULL;
+```
+
+and filtered by `cab` number, via a function
+
+```sql
+CREATE FUNCTION get_speed_durations(cab_id INT) 
+RETURNS TABLE (
+    cab INT, 
+    speed DOUBLE PRECISION, 
+    dir TEXT, 
+    start_time TIMESTAMPTZ, 
+    end_time TIMESTAMPTZ, 
+    duration INTERVAL
+) 
+AS $$
+WITH speed_durations AS (
+    SELECT 
+        cab,
+        avg_speed,
+        max_speed,
+        bucket AS start_time,
+        LEAD(bucket) OVER (
+            PARTITION BY cab ORDER BY bucket
+        ) AS end_time,
+        LEAD(bucket) OVER (PARTITION BY cab ORDER BY bucket) - bucket AS duration
+    FROM telemetry_10secs
+)
+SELECT * FROM speed_durations WHERE end_time IS NOT NULL AND cab = cab_id;
+$$ LANGUAGE sql;
+
+-- Refresh data
+CALL refresh_continuous_aggregate('telemetry_10secs', NULL, NULL);
+SELECT * FROM get_speed_durations(1);
+```