## 2 Materials and Methods
### The Method--MIIM
\begin{table}
\begin{tabular}{c c c c c} \hline  & **Manufacturer** & **Model** & **Range** & **Angle** & **U (\% = 2)** \\ \hline Laser Tracker & Hexagon & AT960 & 20 m & & 10 \(\mu\)m + 0.4 \(\mu\)m/m \\ \hline Retro-reflectors & Hexagon & Super Cat-Eye & 18 m & \(\pm\)75\({}^{\circ}\) & \({}^{\star}\) \\ \hline \end{tabular} \({}^{\star}\)Data not available; implicit in the results.  
\end{table} 
Table 1: Laser tracker and retro-reflector characteristics. Figure 2: Measured points on the THERATM Zayer MT. machine tool to four corner points of the point grid, where the laser tracker, embedded in the machine's spindle, measures the 3D positions of fiducial points at each corner. This transformation aligns the four data sets, establishing the spatial relationship between the corner points of the point cloud and the fiducial points within a local coordinate system established at the initial measurement station. The second best-fit transformation transfers this data set to the machine tool coordinate system. This is achieved by transforming the coordinates of the four corner points to fit the MT coordinate system using their nominal coordinates. The full automation of the MIIM measurement process eliminates the need for human intervention throughout the entire duration of the batch measurement sequence. This ensures that, as soon as a volumetric error mapping process is completed, the system seamlessly initiates a new measurement sequence. Consequently, hundreds of volumetric error mapping measurements can be conducted fully autonomously over several consecutive days. This process is enabled through closed-loop communication between the laser tracker controller and the machine tool controller. As the machine tool moves to the next measurement point within the point cloud, the laser tracker controller receives a trigger to perform distance measurements at each fiducial point. Similarly, once the laser tracker completes its measurement, the machine tool controller is signalled to proceed to the next measurement point. The closed-loop communication between the laser tracker controller and the machine tool controller is orchestrated by the metrology software that is used to execute the measurement sequence. Thus, the SpatialAnalyzer(r) 2023.2 software (Hexagon, Stockholm, Sweden) is utilized, providing all the necessary functionalities to facilitate seamless bidirectional communication with the machine tool controller. As illustrated in Figure 3, the laptop running the metrology software is connected to the laser tracker controller (integrated into the machine tool head) and the machine tool controller via the machine's PLC using a TCP/IP connection. Alternatively, for long tests, the laser tracker can also connect wirelessly via a Wi-Fi network. On the laser tracker controller side, signal transmission and reception are managed using various functionalities provided within the Measurement Plan environment of Spatial Analyzer(r). On the machine tool controller side, specific logic has been implemented within the machine tool's PLC environment to enable signal exchange. This is achieved through a  
Figure 3: Connection setup between the laser tracker and machine tool controllers. CNC logic-based subprogram, which facilitates the modification of CNC variables within the machine's PLC. In this setup, the main measurement CNC program, introduced by the technician, invokes the subprogram to enable CNC variable modifications, allowing the measurement process to operate in a fully autonomous mode. Currently, this capability has been established for HEIDENHAIN TNC7 (Dr. Johannes Heidenhain GmbH, Traunreut, Germany) and SIEMENS 840 C (Siemens AG, Munich, Germany) controllers.