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https://github.com/axiscommunications/opc-ua-gaugereader-acap

Small example ACAP application that reads analog gauges with video analytics and exposes the value via OPC UA.
https://github.com/axiscommunications/opc-ua-gaugereader-acap

acap axis industry-4 industry-40 industry40 opc opc-ua opcua opencv video-analytics

Last synced: 12 months ago
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Small example ACAP application that reads analog gauges with video analytics and exposes the value via OPC UA.

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README 

          
*Copyright (C) 2025, Axis Communications AB, Lund, Sweden. All Rights Reserved.*



# OPC UA Gauge Reader ACAP



[![Build ACAP packages](https://github.com/AxisCommunications/opc-ua-gaugereader-acap/actions/workflows/build.yml/badge.svg)](https://github.com/AxisCommunications/opc-ua-gaugereader-acap/actions/workflows/build.yml)

[![GitHub Super-Linter](https://github.com/AxisCommunications/opc-ua-gaugereader-acap/actions/workflows/super-linter.yml/badge.svg)](https://github.com/AxisCommunications/opc-ua-gaugereader-acap/actions/workflows/super-linter.yml)



![Image of a water level gauge](images/water_level_gauge.jpg)



This repository contains the source code to build a small example

[ACAP version 4](https://axiscommunications.github.io/acap-documentation/)

(native) application that reads an analog gauge using video analytics with

[OpenCV](https://opencv.org/)

and exposes the value through a built-in

[OPC UA](https://en.wikipedia.org/wiki/OPC_Unified_Architecture)

([open62541](https://open62541.org/)) server.



![Architectural overview](images/acap_architecture.svg)



The exposed value is in percent.



> [!NOTE]

> Even if this application would fit right into your usecase, its purpose is

> above all to serve as an example and boilerplate rather than being ready for

> production.



## Example Use Cases



> The following examples assume that you have a [SCADA](https://en.wikipedia.org/wiki/SCADA) (Supervisory

Control And Data Acquisition) system or a [PLC](https://en.wikipedia.org/wiki/Programmable_logic_controller) (Programmable Logic Controller) system with OPC UA as the communication protocol and you want to take advantage of the Axis device capabilities to enrich or complement your operations.



Analog gauges are common in the industry, and it is often impossible to add

digital sensors due to regulations or warranty restrictions. However, having a

human operator monitor these gauges (which is what is done today) is

inconvenient and error-prone. Instead, we can use an IP camera with very basic

video analysis to automatically capture the digital reading and feed it into

the industrial system. Automating the capture of digital values from analog

gauges opens up a multitude of possibilities.



For example:



- shutdown or start a PLC process if a gauge reading exceeds or falls below a specified threshold

- generate alarms when the gauge reading goes outside a predefined range

- display real-time gauge values within the SCADA server's operational interface

- maintain historical logs of gauge values to track changes over time



> [!WARNING]

> Please note that any analytic process can never be 100% accurate and the system designer has to account for this.



## Build



The build process uses the

[ACAP SDK build container](https://hub.docker.com/r/axisecp/acap-sdk)

and Docker or Podman.



The Docker and Podman commands are integrated in the [Makefile](Makefile), so

if you have Docker or Podman and `make` on your computer all you need to do is:



```sh

make dockerbuild

```



or



```sh

make podmanbuild

```



or perhaps build in parallel:



```sh

make -j dockerbuild

```



alternatively



```sh

make -j podmanbuild

```



If you do have Docker but no `make` on your system:



```sh

# 32-bit ARM, e.g. ARTPEC-6- and ARTPEC-7-based devices

DOCKER_BUILDKIT=1 docker build --build-arg ARCH=armv7hf -o type=local,dest=. .

# 64-bit ARM, e.g. ARTPEC-8 and ARTPEC-9-based devices

DOCKER_BUILDKIT=1 docker build --build-arg ARCH=aarch64 -o type=local,dest=. .

```



If you do have Podman but no `make` on your system:



```sh

# 32-bit ARM, e.g. ARTPEC-6- and ARTPEC-7-based devices

podman build --build-arg ARCH=armv7hf -o type=local,dest=. .

# 64-bit ARM, e.g. ARTPEC-8 and ARTPEC-9-based devices

podman build --build-arg ARCH=aarch64 -o type=local,dest=. .

```



## Debug



If you would like the application to store the images from each step in the

video analysis to disk for debugging, set the `DEBUG_WRITE` variable for the

build:



```sh

DEBUG_WRITE=y make -j dockerbuild

```



or



```sh

# 32-bit ARM, e.g. ARTPEC-6- and ARTPEC-7-based devices

DOCKER_BUILDKIT=1 docker build --build-arg DEBUG_WRITE=y --build-arg ARCH=armv7hf -o type=local,dest=. .

# 64-bit ARM, e.g. ARTPEC-8 and ARTPEC-9-based devices

DOCKER_BUILDKIT=1 docker build --build-arg DEBUG_WRITE=y --build-arg ARCH=aarch64 -o type=local,dest=. .

```



> [!TIP]

> For Podman, use the same commands using `podman` instead of `docker`.



## Setup



### Manual installation and configuration



Upload the ACAP application file (the file with the `.eap` extension for the

camera's architecture) through the camera's web UI: *Apps->Add app*



When installed, start the application.



![Web UI Screenshot](images/web_ui_open_settings.png)



Open the application's settings page in the web interface (available when the

application is running) by clicking the *Open* button.



![Web UI Screenshot](images/web_ui_settings.png)



In the settings page, simply click in the image to set up the calibration

points in the following order:



1. Center of the gauge

1. Minimum value of the gauge

1. Maximum value of the gauge



The calibration points can also, along with the OPC UA Server port (default is

4840) and clockwise/counterclockwise (default is clockwise), be set directly

through the application's parameter settings, found in the three vertical dots menu:



![Web UI Screenshot](images/web_ui_open_param_settings.png)



![Web UI Screenshot](images/web_ui_param_settings.png)



### Scripted installation and configuration



Use the camera's

[applications/upload.cgi](https://www.axis.com/vapix-library/subjects/t10102231/section/t10036126/display?section=t10036126-t10010609)

to upload the ACAP application file (the file with the `.eap` extension for the

camera's architecture):



```sh

curl -k --anyauth -u root: \

    -F packfil=@OPC_UA_Gauge_Reader__.eap \

    https:///axis-cgi/applications/upload.cgi

```



To

[start (or stop/restart/remove)](https://www.axis.com/vapix-library/subjects/t10102231/section/t10036126/display?section=t10036126-t10010606)

the application, you can make a call like this:



```sh

curl -k --anyauth -u root: \

    'https:///axis-cgi/applications/control.cgi?package=opcuagaugereader&action=start'

```



Use the camera's

[param.cgi](https://www.axis.com/vapix-library/subjects/t10175981/section/t10036014/display)

to set the center/min/max points, as well as clockwise/counterclockwise and the

OPC UA server port number.



The call



```sh

curl -k --anyauth -u root: \

    'https:///axis-cgi/param.cgi?action=list&group=opcuagaugereader'

```



will list the current settings:



```sh

root.Opcuagaugereader.DynamicStringNumber=1

root.Opcuagaugereader.centerX=479

root.Opcuagaugereader.centerY=355

root.Opcuagaugereader.clockwise=1

root.Opcuagaugereader.maxX=678

root.Opcuagaugereader.maxY=165

root.Opcuagaugereader.minX=283

root.Opcuagaugereader.minY=167

root.Opcuagaugereader.port=4840

```



If you want to set the OPC UA server port to e.g. 4842:



```sh

curl -k --anyauth -u root: \

    'https:///axis-cgi/param.cgi?action=update&opcuagaugereader.port=4842'

```



## Usage



Attach an OPC UA client to the port set in ACAP. The client will then be able

to read the value (and its timestamp) from the application's OPC UA server.



> [!NOTE]

> The application will also log the gauge value in the camera's syslog.



### Bonus



In addition to the above, the application will write the extracted gauge

reading as a

[dynamic text overlay](https://www.axis.com/vapix-library/subjects/t10175981/section/t10007638/display?section=t10007638-t10003585)

string. It can then be displayed as camera text overlay—or used by graph

widgets—with the modifier **#D***N*, where *N* is set by the application

parameter `DynamicStringNumber`.



## License



[Apache 2.0](LICENSE)