# Visual-Based Positioning of Aerial Maintenance Platforms on Overhead Transmission Lines
## 5 Discussion
### Comparison with Existing Positioning Techniques
#### 5.2.1 Gnss-imu  
GNSS and IMU are the most important parts of the UAV navigation systems. Currently, GNSS-IMU navigation is the most adopted sensing mode to locate aerial platform in transmission grids. However, this method is restricted by size and weight constraints and sensors can be affected by electromagnetic interference.  
Figure 15: Comparison of the existing positioning techniques.  
\begin{table}
\begin{tabular}{c l l l l} \hline \hline \multicolumn{2}{c}{**Characteristics**} & \multicolumn{1}{c}{**Advantages**} & \multicolumn{1}{c}{**Disadvantages**} & \multicolumn{1}{c}{Works} \\ \hline \multirow{4}{*}{GNSS-IMU} & -Proprioceptive, Ambient & -Independent of the grid & -Size and weight constraints & \\  & -CMSS and IMU are the base of a navigation system & -High accuracy & -High-resolution data is very costly & \\  & -Nitrogen content & -High accuracy & -Not always available (CMSS-defined areas) & [60,61] \\  & -Nitrogen content & -Nitrogen content & -At least 3 satellites should be detected & \\  & -The system can be affected by EMIs & & \\ \hline \multirow{4}{*}{SAR images} & -Eteroceptive, Non-ambient & -Covers vast areas with few images & -Very high-resolution data is very costly & \\  & -Mapping of power lines and towers & -Nise immunity, high accuracy & -Net easy to interpret & \\  & -Dissent monitoring, damaged towers & -Independent of the grid & -Depending on environmental conditions & \\ \hline \multirow{4}{*}{LASER} & -Eteroceptive, Non-ambient & -Detailed 3D data directly available & -Small objects are difficult to detect & \\  & -Mapping of power conductors and towers & -Noise immunity, high accuracy & -High-resolution data is very costly & [38,62,65,64] \\  & -Vegotation monitoring & -Not dependent on external lighting conditions & -Depending on the scanning geometry & \\  & -Fidelity in data acquisition & -Fidelity in data acquisition & -Fidelity in data acquisition & \\ \hline \multirow{4}{*}{Sonar} & -Eteroceptive, Non-ambient & -Easy to implements & -Highly affected by noise & \\  & -Mapping of conductors and pylons & -Non-complex structure & -Low resolution & [67,68] \\  & -Detection of power line components & -Independent of the grid & -Low costs compared to other methods & \\  & -Detect partial discharges in power lines & -Low costs compared to other methods & -Requires high and perpetual current flow & \\  & -Electroceptive, Non-ambient & -Easy to implements & -Safety vulnerabilities & [69,70] \\  & -Inception of power line components & -Non-complex structure & -Medinal constraints & \\  & -Measures the voltage drop across wires & -Not available when power lines are off & -Off-line mode, High computational cost & \\  & -Energy-receptive, Non-ambient & -High flexibility in data acquisition & -The method needs landmarks to correct & \\  & -Vegotation monitoring & -Low costs compared to other methods & -Case parameters affect directly to measurements & [44,49] \\  & -Vampling of conductors and towers & -Potential for diverse applications & -The technique needs high resolution & \\  & -Fault monitoring in power line components & -Noise immunity & -1 depends on lighting conditions & \\ \hline \multirow{4}{*}{Visual} & -Eteroceptive, Non-ambient & -High spatial resolution & -Camnet be obtained through clouds or in & \\  & -Evagot monitoring & -Possibility of height measurements from & -The image quality can be affected by vibrations. & \\  & -Inspection of power line equipment & visual odometry & -Camera parameters directly affect the measurements & \\  & -Mapping of conductors and ground wires & -Low costs compared to other methods & -It depends on lighting and weather conditions & \\  & -Noise immunity & -Dependent of the grid & \\ \hline \hline \end{tabular}
\end{table}
Table 6: Comparison of the existing positioning methods.