This work was supported by National Natural Science Foundation of China (Grant No. 61673327) and Aeronautical Science Foundation of China (Grant No. 20160168001).
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Figure 3
(Color online) UAV autonomous refueling platform. (a) BVS; (b) simulated RCS; (c) CCP.
Figure 4
(Color online) CCP images. (a) CCP images captured by the left camera; (b) CCP images captured by the right camera; (c) sample drawing of the fixed point of CCP image.
Figure 5
(Color online) Preprocessing of image. (a) Three-channel color image; (b) graying the color image; (c) binarization to the grayscale image; (d) median filtering of image.
Figure 6
(Color online) Connected area labeling effect diagram.
Figure 7
(Color online) Effects of different algorithms. (a) Effect diagram of centroid algorithm; (b) effect of the centroid algorithm in the original image; (c) effect image extracted using the Harris algorithm; (d) effect image extracted using the SURF algorithm.
Figure 10
(Color online) Demonstrations of matching effect. (a) Effect of stereo matching of FPs; (b) effect of stereo matching using the ELR algorithm; (c) effect of stereo matching using the SURF algorithm.
Figure 13
(Color online) Structure diagram of tracking control system for AAR and docking of UAV.
Figure 14
(Color online) Actual relative position and expected relative position of UAV. (a) In the $X$-axis; (b) in the $Y$-axis; (c) in the $Z$-axis.
Figure 16
(Color online) Control values for controller output. (a) $~\Delta~\delta_{t}$; (b) $~\Delta~\delta_{a}$; (c) $~\Delta~\delta_{e}$; (d) $~\Delta~\delta_{T}$.
| *3 | ||
| X< | ||
| Internal parameter | Left camera | Right camera |
| $~f_{x}~$ | 2394.3558 | 2325.5075 |
| $~f_{y}~$ | 2393.9677 | 2325.2000 |
| $~u_{0}~$ | 692.7227 | 628.8684 |
| $~v_{0}~$ | 590.8281 | 555.3041 |
| $~k_{1}~$ | 0.0708 | 0.0661 |
| $~k_{2}~$ | $-$0.1293 | 0.0147 |
| $~\gamma~$ | $-$4.5025 | $-$0.4948 |
Calibration of BVS. $~\boldsymbol{A}_{l},~\boldsymbol{A}_{r}~$ and $~\boldsymbol{M}_{l},~\boldsymbol{M}_{r}~$ are obtained from the left and right cameras of BVS, respectively. |
Image acquisition. The left and right cameras of BVS are used to capture the same object simultaneously and the captured images are stored in the form of digital images in the computer. |
Image preprocessing. Graying, binarization, and median filtering are applied to the image. |
Extraction of image FPs. Pixels containing important features of the image are extracted as FPs. |
FP matching. The corresponding relationship between the left and right image FPs is determined. |
3D coordinate calculation. Based on the binocular vision principle, the 3D coordinates of matching FPs are obtained. |
| External parameter | Calibration matrix of BVC |
| Rotation matrix $~\boldsymbol{R}~$ | $~\begin{bmatrix}~{0.9986}~&~{0.0006}~&~{0.0525}~\\~{-0.0006}~&~{1.0000}~&~{-0.0002}~\\~{-0.0525}~&~{0.0002}~&~{0.9986}~\end{bmatrix}~$ |
| Translation matrix $~\boldsymbol{T}~$ | $~\left[\begin{matrix}~{-111.08}~&~{2.9456}~&~{-25.069}~\end{matrix}\right]~^{{\rm~T}}~$ |
|
Find the pixels that are not marked and mark them in the tag matrix. |
|
Find $~y_{r}~$, $~y^{*}~$, $~\hat{x}$ and $~\hat{u}~$. |
| Feature extraction algorithm | Total number of FPs | Number of effective FPs | Effective ratio (%) |
| OSE | 1000 | 1000 | 100 |
| Harris | 15283 | 14796 | 96.81 |
| SURF | 18165 | 16914 | 93.11 |
| Matching algorithm | Total number of pairs | Correct number of pairs | Matching accuracy (%) |
| IHWT | 50 | 50 | 100 |
| ELR | 50 | 43 | 86 |
| SURF | 300 | 135 | 45 |
| Labels of FP | Pixel coordinates of the left image | |
| $~u\text{-}{\rm~axis}~$ coordinates | $~v\text{-}{\rm~axis}~$ coordinates | |
| 1 | 766.3222 | 294.0458 |
| 2 | 841.5005 | 296.4669 |
| 3 | 1065.564 | 452.7329 |
| 4 | 834.3635 | 596.7836 |
| 5 | 610.3694 | 437.7926 |
| Labels of FP | Pixel coordinates of the right image | |
| $~u\text{-}{\rm~axis}~$ coordinates | $~v\text{-}{\rm~axis}~$ coordinates | |
| 1 | 550.1918 | 322.0488 |
| 2 | 625.2786 | 324.3251 |
| 3 | 847.9412 | 481.3774 |
| 4 | 612.4110 | 625.5150 |
| 5 | 392.3321 | 465.6742 |
| Labelstextbackslash coordinates of world CS | Coordinates of the FPs obtained using BVS | ||
| $~X\text{-}{\rm~axis}~$ ($~{\rm~mm}~$) | $~Y\text{-}{\rm~axis}~$ ($~{\rm~mm}~$) | $~Z\text{-}{\rm~axis}~$ ($~{\rm~mm}~$) | |
| 1 | 30.0643 | 55.2186 | 957.0100 |
| 2 | 60.1948 | 55.9709 | 956.9757 |
| 3 | 147.2115 | $-$9.3191 | 943.2886 |
| 4 | 55.9019 | $-$64.4386 | 939.0642 |
| 5 | $-$32.2210 | $-$1.2189 | 947.7082 |
| Labelstextbackslash coordinates of world CS | Coordinates of the FPs obtained via measurement | ||
| $~X\text{-}{\rm~axis}~$ ($~{\rm~mm}~$) | $~Y\text{-}{\rm~axis}~$ ($~{\rm~mm}~$) | $~Z\text{-}{\rm~axis}~$ ($~{\rm~mm}~$) | |
| 1 | 29.4972 | 55.6821 | 955.7350 |
| 2 | 59.5163 | 54.7009 | 955.6184 |
| 3 | 147.5596 | $-$7.6893 | 946.1418 |
| 4 | 55.4418 | $-$64.1295 | 938.7077 |
| 5 | $-$32.5715 | $-$1.6992 | 946.9239 |
| Parameter variables | Parameter values |
| Position of UAV & RCS (m) | (0, 0, 0) & (52.2303, 7.2426, 948.8093) |
| Pose of UAV & RCS ($^{\circ}$) | (0, 0, 0) & ($-$0.083, $-$0.1468, 0.9891) |
| Speed of UAV & RCS (m/s) | 20 |
| Acceleration of UAV & RCS (m$~/{\rm~s}^{2}$) | 20 |
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