3.3.1. ANN Training Data Collection

In order to improve the accuracy of the coordinates of the key points, the study needs to collect sufficient data to develop an ANN model. The spacing of the pole and the lift height of the small-scale high formwork model set were specified. The model set first was positioned on a movement equipment and moved along the X direction at interval 1 mm, and then the model set was moved along the Y direction at interval 1 mm from 1 mm-10 mm. Finally, the model set was moved along the Z direction from 1 mm to 10 mm at interval 1 mm. Every movement was scanned. Thus, the model set was scanned 30 times, and the collected 30 datasets were used to develop an ANN model to predict the coordinates of the cross points of the poles and tubes. The moving distance is specified as 1 mm, so that the coordinates of the key points at t moment can be calculated based on the coordinates at *t* − 1 moment, as shown in Equation (6). The initial coordinates of the key points were generated from total station measurement.

$$P\_i^t \left( \begin{array}{c} \mathbf{x}\_i^t \\ \mathbf{y}\_i^t \\ z\_i^t \end{array} \right) = P\_i^{t-1} \left( \begin{array}{c} \mathbf{x}\_i^{t-1} + 1 \text{ mm} \left( \stackrel{\rightarrow}{\mathbf{X}} \right) \\ \mathbf{y}\_i^{t-1} + 1 \text{ mm} \left( \stackrel{\rightarrow}{\mathbf{Y}} \right) \\ z\_i^{t-1} + 1 \text{ mm} \left( \stackrel{\rightarrow}{\mathbf{Z}} \right) \end{array} \right) \tag{6}$$

where *P<sup>t</sup> i* ⎛ ⎝ *xt i yt i zt i* ⎞ ⎠ indicates the coordinate of the *i* point at *t* moment; *xt*−<sup>1</sup> *i* + 1 mm( → *X*)

indicates the model move along the X axis at specified value 1 mm, so the x coordinate of the *i* point at *t* moment equal to the x coordinate of the point at *t* − 1 moment add 1 mm, but the *y* and *z* coordinates of the *i* point at *t* moment are the same as that at *t* − 1 moment.
