
Fig. 1.
Traditional multi-line laser system and tracking ball joint calibration schematic diagram.

Fig. 2.
Track system structure diagram.

Fig. 3.
Hardware controller, (a) hardware circuit board, (b) circuit board structure diagram.

Fig. 4.
Signal timing diagram of the laser controller.

Fig. 5.
Binocular tracking system and cross pole.

Fig. 6.
The conversion relationship between the multi-line laser system and the tracking ball cage.

Fig. 7.
Joint calibration schematic diagram.

Fig. 8.
Joint calibration of physical structure drawing.

Fig. 9.
Joint calibration flow chart.

Fig. 10.
Schematic diagram of stitching the tracking system.

Fig. 11.
Accuracy verification of joint calibration.
Table 1.
Binocular hardware parameters.
| Camera | Cross pole | ||
|---|---|---|---|
| Resolution [pixel2] | 2248×2048 | Size [mm2] | 1200×1200 |
| Focal length [mm] | 8 | Coded point number | 16 |
| Frame rate [s−1] | 90 | Coded point size [mm2] | 80×80 |
| Field range [mm] | 3000~4000 | ||
| Distance [mm] | 2000~3000 |

Fig. 12.
(a) Cross pole; (b) Three-dimensional coordinates and encoded values of points on the cross pole.

Fig. 13.
The results of left and right image coding point detection.

Fig. 14.
Calibration error.

Fig. 15.
The images of the ball cage were captured from various perspectives.

Fig. 16.
(a) Effect of coding point recognition, (b) 3D coordinates of all reflecting points on the ball cage.

Fig. 17.
Multi-line laser and tracking ball cage joint calibration.

Fig. 18.
The 3D data and the transformation relationship of the cross pole within the multi-line laser system and the binocular tracking system.

Fig. 19.
The conversion relationship between the tracking ball cage and the binocular tracking system.

Fig. 20.
Schematic diagram of the joint calibration comparison, (a) Joint calibration based on a flat plate; (b) Joint calibration based on a cross pole.

Fig. 21.
Comparison of joint calibration accuracy.
Table 4.
Comparison test parameters for joint calibration.
| The method in this paper | Traditional methods | |
| Calibrated object | Cross pole | Planar calibration board |
| Field of view | 3000 mm × 4000 mm | |
| Depth of field range | 800 mm × 1000 mm | |
| Object test | Cross pole | |
| Camera – resolution | 2448 × 2048 | |
| Camera – focal length | 8 mm | |
| Calibration results | ||

Fig. 22.
Standard ball.

Fig. 23.
Standard ball reconstruction process based on the tracking system.

Fig. 24.
Error plots for both methods.
Table 5.
Comparison of precision between the calibration algorithm proposed in this article and the traditional flat-plate calibration algorithm.
| Number | Calibration algorithm of this paper (Method 1) | Calibration algorithm of traditional plate calibration (Method 2) | ||||
|---|---|---|---|---|---|---|
| Di | DA | DB | Di | DA | DB | |
| 1 | 300.0456 | 60.0247 | 60.0182 | 300.1547 | 60.0628 | 60.0978 |
| 2 | 300.0578 | 60.0341 | 60.0138 | 300.1236 | 60.1174 | 60.1147 |
| 3 | 300.0372 | 60.0297 | 60.0142 | 300.0412 | 60.1524 | 60.1340 |
| 4 | 300.0424 | 60.0225 | 60.0150 | 300.0824 | 60.0925 | 60.0941 |
| 5 | 300.0447 | 60.0279 | 60.0118 | 300.1471 | 60.0817 | 60.1119 |
| 6 | 300.0481 | 60.0248 | 60.0171 | 300.0758 | 60.1247 | 60.1477 |
| 7 | 300.0525 | 60.0121 | 60.0121 | 300.110 | 60.0852 | 60.0701 |
| 8 | 300.0473 | 60.0195 | 60.0177 | 300.0914 | 60.1264 | 60.1517 |
| Mean error | 0.0454 | 0.0220 | 0.0306 | 0.1593 | 0.1030 | 0.1121 |

Fig. 25.
Other objects are reconstructed based on a multi-line laser tracking system.