BIM - Building Information Modeling

Overview

This example puts a building model in the DTaaS library and gives each of its rooms a simulated temperature sensor. The building is the FZK-Haus, a two-storey house modelled by the Karlsruhe Institute of Technology (KIT) as an IFC example. Its model has 7 rooms (IfcSpace) and no sensors, so the example proposes one temperature sensor per room. Rooms are not drawn in the 3D view, so each sensor is bound by its IFC GlobalId to a wall or column inside the room, the one nearest to the room's centre that no other room has taken. When a room has none left, the sensor goes on another drawn object in it, such as a door.

The Buildings page of the DTaaS client draws the model from the library. The binding manifest written by this example tells the page which reading belongs to which room. A publisher sends a simulated temperature for every room over MQTT, on the topics the manifest lists.

The model is AC20-FZK-Haus.ifc from the KIT IFC examples, which KIT provides for unrestricted use. Its content is unchanged, and only its line endings are stored as LF. As KIT asks, publications that use it credit the Institute for Automation and Applied Informatics (IAI) / Karlsruhe Institute of Technology (KIT).

Example Structure

File	What it does
models/fzk_haus.ifc	The building model, IFC4
lifecycle/make_manifest.py	Proposes one sensor per room, places it on a wall of the room and writes the binding manifest
lifecycle/publish_readings.py	Publishes a simulated temperature per room over MQTT
lifecycle/show_readings.py	Prints the first readings that reach the broker
lifecycle/requirements.txt	The IFC converters from ifc-utils and the MQTT client
lifecycle/constraints.txt	The versions of the packages those tools pull in, each at least ten days old when pinned

The create phase writes four files into /workspace/common/models, the folder the Buildings page reads:

File	Contents
fzk_haus.ifc	A copy of the building model
fzk_haus.glb	The geometry, so the page does not convert the model in the browser
fzk_haus.json	The property tree shown when you click an object
fzk_haus.manifest.json	One binding per room, from room to MQTT topic

Digital Twin Configuration

Asset Type	Names of Assets	Visibility	Reuse in Other Examples
Model	fzk_haus.ifc	Common	Yes
Tools	ifc-explorer, ifc-converter	Installed by create	Yes

The publisher reads the broker from these environment variables:

Variable	Default	Meaning
MQTT_HOST	localhost	Host name of the MQTT broker
MQTT_PORT	1883	MQTT port of the broker
MQTT_USERNAME	not set	User name, when the broker asks for one
MQTT_PASSWORD	not set	Password, when the broker asks for one
MQTT_TLS	not set	Set to 1 to connect over TLS, for example on port 8883

Without MQTT_TLS, the user name and password travel unencrypted, so set it whenever the broker is not on the same machine.

The lifecycle scripts work from any directory, as the other examples do. Two more variables change where they read and write:

Variable	Default	Meaning
EXAMPLES_PATH	the repository root	Where models/fzk_haus.ifc is read from
WORKSPACE	the folder above EXAMPLES_PATH, /workspace inside the workspace	The library whose common/models receives the model

Lifecycle Phases

Lifecycle Phase	Completed Tasks
Create	Installs the tools, places the model and writes the derived files
Execute	Starts the publisher in the background
Terminate	Stops the publisher and clears its log
Clean	Clears the publisher log and PID file

Run the Example

Change to the example directory:

cd /workspace/examples/digital_twins/fzk_haus

If required, give the lifecycle scripts execute permission:

chmod +x lifecycle/*

Create

Installs ifc-explorer, ifc-converter and paho-mqtt into a virtual environment in .venv. Then copies the model into /workspace/common/models and writes the geometry, the property tree and the binding manifest beside it. This takes about a minute, most of it for the installation.

lifecycle/create

Open Buildings in the DTaaS menu and choose Projekt-FZK-Haus, the name the model gives its project, to see it.

Execute

Starts publishing a temperature for each room every two seconds. Point it at the MQTT broker of your installation first, for example the one installed with the DTaaS platform services:

export MQTT_HOST=<broker host>
lifecycle/execute

Each reading goes to dtaas/examples/fzk-haus/room-NN/temperature as one line of comma-separated fields:

timestamp,measurement,type,unit,value
20261013T10:00:00,temperature,simulation,°C,21.40

The type field says simulation, so a subscriber can tell these values apart from measured ones. The log is in publisher.log.

To see the readings arrive through the broker, print the first round of them:

.venv/bin/python lifecycle/show_readings.py /workspace/common/models/fzk_haus.manifest.json

It prints one line per room, such as 1, Flur temperature: 22.10 °C at 12:02:14, and stops with an error when no reading arrives within 10 seconds.

Terminate

Stops the publisher and removes its log:

lifecycle/terminate

Current Limits

The Buildings page draws the model and resolves the manifest, but the DTaaS client does not subscribe to MQTT yet. Until it does, the readings reach any other MQTT subscriber, such as a dashboard, and not the page. The demo video shows this: the readings reach the terminal through the broker, and the page draws the model and its sensors, whose cards wait for a first reading.

References

The converters come from the ifc-utils repository. The manifest format and the Buildings page are described in DTaaS issue 1762.