Using the solution

Triggering inspection remotely with an MQTT command

To remotelly trigger taking pictures and running inference on them, you can use MQTT to publish commands to the camera client.

The main use case for this is to have an external inspection station, which notices that an object is on the conveyor belt, using sensors. When the object to be inspected is in front of the camera, this external system can send an MQTT message to the VIAI Edge application to trigger the camera and visual inspection of the image.

Another use case is to have an external physical system with push buttons, to let human operators easily trigger taking an image and running inference. Pressing the button can send MQTT messages to control this application.

The utility listens for MQTT commands in topic: viai/commands. It publishes MQTT results on the topic: viai/results. Currently, the following MQTT payload commands have been implemented: get_frame, exit and quit (both exit and quit close the utility gracefully).

Run on Edge Server

Start the utility in daemon mode, with both listening for commands over MQTT, as well as publishing the ML inference results in another MQTT topic:

 export ML_HOST=viai-model
 export MQTT_HOST=mosquitto

 python3 camera_client.py --protocol usb --address /dev/video0 --device_id 'usbcam' \
     --mode mqtt_sub --mqtt --mqtt_host ${MQTT_HOST} --sleep 0 --ml --ml_host ${ML_HOST}

If everything goes well, the utility starts in daemon mode and outputs similar to:

 2022-09-13 06:45:23,846 - root - INFO - Starting MQTT client. Publishing results to: viai/results
 Local network MQTT connected with result code 0
 Subscribing to MQTT topic: viai/commands
 MQTT subscription result code: (0, 1)

On a second console window, subscribe to the MQTT inference results.

Note: this requires installing the mosquitto MQTT client on your laptop or running these commands on the VIAI Edge server:
```
 mosquitto_sub -h ${MQTT_HOST} -t viai/results
```

On a third console window, publish the trigger message to the VIAI Edge utility:

 mosquitto_pub -h ${MQTT_HOST}-t viai/commands -m get_frame

If successful, your VIAI Edge utility window should display:

 INFO:root:MQTT command received: get_frame
 INFO:root:{'predictionResult':...
 INFO:root:Transmitting ML inference results to local MQTT
 INFO:root:Local MQTT transmit complete

and your mosquitto_sub window should display the ML inspection result payload:

 {"predictionResult":...
 ...

Quit the utility by sending a quit message with:
```
 mosquitto_pub -h ${MQTT_HOST} -t viai/commands -m quit
```
Which should close the utility on the VIAI Edge server and output:
```
 INFO:root:Quit command received via MQTT..
```