## 3 Results
### Accuracy Test
#### 3.1.2 Snow Sculpture Measurement  
A snow sculpture is selected with the approximate size of 3000 mm \(\times\) 3000 mm \(\times\) 3000 mm. Twenty feature points are selected on the surface of the snow sculpture, and 20 blue round marking patches with a diameter of about 2 mm and a thickness of 0.1 mm are attached to these points, as shown in Figure 10. At first, a laser tracker is used to measure each pair of feature points for three times, and an average is derived. The distance between two points is then calculated as the standard value. Next, the center of corresponding blue marking patches are in the point cloud generated by the structured-light device. The distance between them is obtained. The average of three measurements is taken as the final measurement. The resultsare shown in Table 2.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Standard Value**} & \multicolumn{4}{c}{**Measurement Value**} & \multicolumn{4}{c}{**Error**} \\ \cline{2-13}  & \(d_{x}\) & \(d_{y}\) & \(d_{z}\) & \(d\) & \(d^{\prime}x\) & \(d^{\prime}y\) & \(d^{\prime}z\) & \(d^{\prime}\) & \(\Delta d_{x}\) & \(\Delta d_{y}\) & \(\Delta d_{z}\) & \(\Delta d\) \\  & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** \\ \hline
1 & 0.057 & 52.398 & 62.419 & 81.497 & 0.013 & 52.479 & 62.464 & 81.583 & \(-\)0.044 & 0.081 & 0.045 & 0.086 \\
2 & 66.200 & 66.276 & 02.64 & 93.675 & 66.180 & 66.180 & 0.331 & 93.593 & \(-\)0.020 & \(-\)0.096 & 0.067 & \(-\)0.082 \\
3 & 51.145 & 1.956 & 58.665 & 77.854 & 51.202 & 1.880 & 58.536 & 77.792 & 0.057 & \(-\)0.076 & \(-\)0.129 & \(-\)0.062 \\
4 & 0.273 & 118.477 & 85.960 & 146.376 & 0.204 & 118.576 & 85.975 & 146.627 & \(-\)0.069 & 0.299 & 0.015 & 0.251 \\
5 & 119.601 & 2.100 & 87.924 & 148.457 & 119.700 & 2.111 & 87.905 & 148.526 & 0.099 & 0.011 & \(-\)0.019 & 0.069 \\
6 & 0.289 & 57.164 & 119.454 & 132.428 & 0.231 & 57.158 & 119.615 & 132.570 & \(-\)0.058 & \(-\)0.006 & 0.161 & 0.142 \\
7 & 116.334 & 60.623 & 0.097 & 131.182 & 116.365 & 60.617 & 0.088 & 131.207 & 0.031 & \(-\)0.006 & \(-\)0.009 & 0.025 \\
8 & 44.990 & 118.157 & 0.348 & 126.433 & 44.984 & 118.154 & 0.411 & 126.428 & \(-\)0.006 & \(-\)0.003 & 0.063 & \(-\)0.005 \\
9 & 62.877 & 2.721 & 120.578 & 136.015 & 62.825 & 2.740 & 120.537 & 135.955 & \(-\)0.052 & 0.019 & \(-\)0.041 & \(-\)0.060 \\
10 & 0.200 & 69.578 & 123.365 & 141.634 & 0.177 & 69.562 & 123.323 & 141.589 & \(-\)0.023 & \(-\)0.016 & \(-\)0.042 & \(-\)0.045 \\
11 & 122.311 & 7.598 & 0.544 & 122.548 & 122.284 & 7.550 & 0.503 & 122.518 & \(-\)0.027 & \(-\)0.048 & \(-\)0.041 & \(-\)0.030 \\
12 & 0.005 & 117.543 & 0.199 & 117.543 & 0.030 & 117.528 & 0.135 & 117.528 & 0.025 & \(-\)0.015 & \(-\)0.064 & \(-\)0.015 \\
13 & 0.025 & 1.913 & 116.542 & 116.558 & 0.040 & 2.322 & 116.855 & 116.878 & 0.015 & 0.049 & 0.313 & 0.320 \\
**Mean error (mm)** & & & & & & & & & & **0.046** & **0.043** & **0.025** & **0.046** \\ RMS errors (mm) & & & & & & & & & & & **0.049** & **0.147** & **0.113** & **0.125** \\ \hline \hline \end{tabular}
\end{table}
Table 1: The result of standard cube measurement.  
Figure 10: Snow sculpture measurement; **(a)** 10 feature distances selected on the snow sculpture; **(b)** 10 feature distances on the 3D point cloud.  
The RMS error of the feature distance is 0.722, and (0.755, 0.588, 0.862) in \(X\), \(Y\) and \(Z\) directions. The mean error of the feature distance is 0.574 mm, and the maximum errors in \(X\), \(Y\) and \(Z\) directions are 1.522 mm, 1.033 mm and 1.409 mm, respectively.