## 4 Recognition and Operation of Facade Protrusions
### Matching of Dimensional Parameters  
The concept of dimensional parameter matching: The robot compares the dimensions of the target object obtained by vision with all dimensions under that category of the object in the dimensional database and outputs the dimension with the smallest difference as the dimension. The matching of dimensional parameters relies on the establishment of the dimension database and the facade protrusion profile dimensions obtained by the vision system. The key idea of dimensional parameters matching is to compare the dimensional information obtained by binocular vision with the data in dimension database \(D\) to obtain accurate dimensional information \(\{D\,|\,d1,d2,...,dn\}\).  
The specific steps of the dimensional data matching are as follows: firstly, according to the recognized facade protrusion category z, the corresponding dimension of the facade protrusion is obtained from the database di. Then, the dimensions obtained by binocular vision h are compared with the different categories of the facade protrusion in the database to find the difference, and the dimension with the smallest difference is selected as the final result. The pseudocode for dimensional parameter matching is as follows (Algorithm 1):  
```
Input: facade-protrusion category z, dimensional information obtained by binocular vision h, dimension database D Output: dimension of the facade-protrusion s
1:\(k\)\(\leftarrow\)\(\,|\,d1\) -\(h1\,/\,/\)Initial difference
2:\(b\)\(\leftarrow\)\(0\,/\,/\)Difference between visually obtained dimension and dimension parameter in the database
3:\(s\)\(\leftarrow\)\(0\)
4:for each \(di\)do/Obtain the minimum difference through loop comparison
5:\(b\)\(\leftarrow\)\(\,|\,di\) -\(h1\,\)
6:if(\(b\) <\(k\))then
7:\(k\)\(\leftarrow\)\(b\)
8:\(s\)\(\leftarrow\)\(di\)/Take the standard dimension with the smallest difference as the final dimension
9:endif
10:endfor
11:return\(s\)
```  
**Algorithm 1**Dimensional parameter-matching algorithm  
The main categories of facade protrusions are pipes, flanges, fasteners, fire-fighting accessories and instrument housings. For the establishment of the dimension database in this paper, certain pipes and fittings were selected as objects. The three-dimensional information parameters are derived from GB/T 5312-1999 and GB/T 8163-1999 dimension tables, and the characteristic dimensions include nominal through the diameter, steel pipe outer diameter and steel pipe wall thickness. Taking the dimensional data of the steel pipe as an example, the dimension database of the steel pipe is shown in Table 1.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Feature Categories** & \begin{tabular}{c} **Diameter** \\ **(mm)** \\ \end{tabular} & \
\begin{tabular}{c} **Outer Diameter** \\ **(mm)** \\ \end{tabular} &
\begin{tabular}{c} **Thickness** \\ **(mm)** \\ \end{tabular} \\ \hline seamless steel tubes for the transport of & & & \\ fluids 1 & & & \\ seamless steel tubes for the transport of & & & \\ fluids 2 & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Dimensional parameters of different types of steel tubes as facade protrusion.