Drone Cell Tower inspection is mainly focused on acquiring the necessary images according to a precise flight planning strategy to ensure a full analysis of the different components and geometries during the upcoming stages.
IN THIS ARTICLE
Requirements
Designing the data acquisition plan
Setting references
Mission list
Signal loss scenarios
Camera parameters
General recommendations
No obstacles around the Cell tower:
Helix mission
With obstacles around the Cell tower:
Orbit mission
Cylinder mission
Single vertical mission
Visual inspection missions
Underneath orbit mission
Orbit line of sight mission
Manual images mission
Requirements
Quality of images
To design a good data acquisition, it is important to ensure images show the greatest possible detail in the structure and antennas:
- Antenna images from all possible angles, to get the shape of the antenna as well as the rear photo of the antenna.
- Port configuration of the bottom. The image beneath the antenna is essential for identification.
- Tower structure, including the foundation and ground cabinets.
To check if the quality of the images captured is good enough, please refer to the real-time video feedback and the quality of the pictures taken from the drone.
Quality of the scene reconstruction
The final 3D model should meet the following criteria:
- Low noise level.
- Surface definition and defined edges.
- High point density.
- High relative accuracy, including the correct scale, orientation, and verticality of the tower.
Designing the data acquisition plan
Flight planning depends on the tower structure, the number of points of interest, specific site requirements, and tower dimensions.
As a generic example, we can consider a 35m (115 feet) cell tower with two antenna nests. Ideally, the missions to perform would be:
- One Helix per tower structure if there are no obstacles around the tower (orange).
- One Underneath orbit per antenna nest to get high-quality images from the lower side of the antennas, connection board, etc, (blue).
Or:
- One Cylinder per tower structure (yellow). If the cylinder mission can't be performed due to obstacles, e.g., guyed towers, perform multiple single verticals.
- One Orbit per antenna nest (green).
- One Underneath orbit per antenna nest to get high-quality images from the lower side of the antennas, connection board, etc, (blue).
Setting references
The Cell Tower asset locations are based on some references recorded by the operator after taking off and while manually piloting the drone in the air.
After selecting the Cell Tower asset in the new plan creation window, follow the onboarding guide and determination of the Cell tower lowest point (optional), Cell tower center, and the Cell tower highest point.
Set the Cell tower lowest point (optional)
Some locations do not allow users to take off at the same height as the cell tower base. This includes cases like rooftops or towers located on top of hills. To optimize the missions for these use cases, users can set the Cell tower lowest point.
An animated description will guide the user to determine the Cell tower lowest point reference:
- Align the drone with the lowest point of the tower.
- Ensure the camera angle is 0°, or tap on Set to 0o.
- Point the camera at the base of the tower.
- Tap on Next to confirm the current tower lowest point reference.
Set the Cell tower center
This is done to be as accurate as possible to get the center reference of the cell tower to be scanned, warranting that all the flights within the same cell tower asset will share the same center position.
If Return to Home (RTH) height is lower than the current drone height when setting the center reference, a pop-up dialog will ask the user to confirm to update that value to the current height. This way, the RTH will be a safe, known height higher than the tower to avoid potential collisions in case of an RTH.
An animated description will guide the user to determine the cell tower center reference:
- Place the drone on top of the tower (several meters above for safety).
- Ensure height is higher than 10 m.
- Ensure the camera angle is -90°, or tap on Set to -90o.
- Point the camera at the center of the tower.
- Tap on Next to confirm the current tower center reference.
Set the Cell tower highest point
The next step is to determine the Cell tower highest point. This value is used for planning Helix, Cylinder, and Single Vertical missions.
An animated description will guide the user to determine the cell tower highest point reference:
- Align the drone with the highest point of the tower.
- Ensure the drone height is higher than 10 meters.
- Ensure the camera angle is 0°, or tap on Set to 0o.
- Point the camera at the top of the tower.
- Tap Next to confirm the current tower highest point reference.
Mission list
When the cell tower references have been set, the mission list is displayed. It is divided into 3D Model (No obstacles and With obstacles missions), and Visual inspection categories containing all the missions to reconstruct and inspect cell tower assets efficiently.
It also shows the cell tower reference values recorded at the previous stages and provides the ability to reset them. Select one of the missions and tap Next to enter the mission settings. After finishing any of the missions (except Single vertical), the Cell tower mission list is displayed, showing the number of finished missions and the total number of images or videos for each mission type. It is then possible to execute another mission by selecting it and tapping Next or to exit the mission list by tapping on the cross 
at the top right side.
Signal loss scenarios
The PIX4Dcapture Pro missions are specially designed to deal with signal loss scenarios, as it can be a common case. If the signal is lost during a mission, the drone will continue flying the mission and triggering the images. If once the mission is finished the signal is not back, then the drone will execute the selected signal lost action (RTH, Hover, Land). This ensures the integrity of the data.
Camera parameters
In order to avoid acquiring overexposed or underexposed images, we recommend using the light condition templates (sunny, cloudy) to load the recommended following white balance (WB) and exposure compensation values (EV) for the different mission types.
Conditions
EV for Orbit and Cylinder missions
EV for Underneath missions
White Balance
Sunny
-0.7
2
Sunny
Cloudy
0.0
2
Sunny
General recommendations
In order to obtain optimal results, please make sure to follow our recommendations:
- Calibrate the drone sensors (compass, IMU, etc.) if you are flying in a new location.
- Place your drone take-off position at least 20m away from the upcoming mission flight path in a safe place.
- Ensure you have a strong GPS signal (wait one minute before taking off for the first time or after every battery switch).
- Do not close PIX4Dcapture Pro while performing a mission.
- Keep the radius as constant as possible for all the missions performed.
When there are no obstacles around a cell tower, the 3D model can be obtained by flying a single Helix mission.
Helix mission
The Helix mission is a fully automatic solution to obtain a complete 3D model of a Cell Tower. It is composed of successive orbits that make a full scan of the structure without any manual interaction. It is recommended for cases where there are no obstacles around the tower, as it can not be truncated, and it is meant to replace cylinders and orbits for these cases.
The following parameters can be adjusted.
Height of the helix base
2D distance from the helix to the cell tower center position
Overlap level between images
When there are obstacles around a cell tower, the 3D model can be obtained by flying several mission types: Orbit, Cylinder, or Single verticals. It is highly recommended to keep the radius as constant as possible for all the missions performed.
Orbit mission
The main goal of the Orbit missions is to acquire images with high overlap around the point of interest. In the case of cell towers, this is typically the area of an isolated antenna or of antenna nests, where a group of antennas is located at the same level. Learn which types of antennas are recognized by PIX4Dinspect in AI recognition of inventories - PIX4Dinspect.
In order to get an optimally reconstructed digital twin, it is recommended to perform 1 Orbit mission per antenna nest and to increase the number of images in the most interesting areas. These areas are normally where the antennas are located, but orbits can be executed at any level where the user wants to have a higher definition/density in the digital twin.
Rather than selecting them from the mission settings, values such as Camera angle, Radius, and Height are based on the video feed on the screen, so from the current drone position, which is manually adjusted with the drone's controller. This is to ensure that we are viewing what we are going to scan, so having a correct point of view for the orbit images.
The following parameters can be adjusted.
Time interval capture: time-optimized continuous flow
Stop at capture point: stability and image centering optimized flow
Time interval capture
Flight direction allows users to define the direction of a circular mission
Clockwise or Counterclockwise
Mission truncation allows users to define a truncation angle for the mission, providing flexibility in mission design
0o - 315o
* Recommended value is based on a 2 m radius structure. If the structure is wider, then the radius should be increased accordingly.
** Different capture modes are supported for DJI drone
Cylinder mission
The purpose of the Cylinder mission is to ensure the full scanning of the tower. The overlap between images can be lower as usually there is no need to get a high density/definition point cloud from the tower structure like the one needed for antennas.
It is recommended to perform only 1 Cylinder mission per cell tower.
The following parameters can be adjusted.
* Recommended value is based on a 2 m radius structure. If the structure is wider, then the radius should be increased accordingly.
The following values are automatically calculated:
- Camera angle: Values will be interpolated along each vertical between -45o at the mission maximum height and the resulting value from looking to the tower base from the mission minimum height.
- Mission maximum height: Maximum height for the drone to fly. The drone will start the first line from the top, at a height of Mission max height = Cell tower highest point + mission radius.
Single vertical mission
Single vertical missions are meant to replace or complement a Cylinder mission in case it can't be completely performed due to obstacles (e.g., guyed towers).
The dashed circle in the map view represents the selected radius. When the drone moves around the point of interest, the starting position of the Single vertical is dynamically projected over it. Once a Single vertical has been completed, the user remains in the mission view, and a green check appears on its location as a visual reference for upcoming Single verticals.
The following parameters can be adjusted.
Down to Up
* If multiple Single vertical missions are performed, it is recommended to use the same radius.
The following values are automatically calculated:
- Camera angle: Values will be interpolated along each vertical between -45o at the mission maximum height and the resulting value from looking to the tower base from the mission minimum height.
- The Max flight height: Maximum height for the drone to fly. The drone will start the first line from the top, at a height of Mission max height = Cell tower highest point + mission radius.
Visual inspection missions
Underneath orbit mission
It is designed to get high-quality images from the lower side of the antennas, connection board, cables, etc. Basically, the strategy is the same as for the orbit mission (1 Underneath orbit mission per antenna nest) but with a lower number of images.
The following parameters can be adjusted.
* Recommended value is based on a 2 m radius structure. If the structure is wider, then the radius should be increased accordingly.
Orbit line of sight mission
The Orbit line of sight mission is designed to get a 360o view of the cell tower surroundings. It helps to identify obstacles around the asset, and also check the visual line with other locations. It executes an orbit from the current drone height looking outwards the asset.
In order to start an Orbit line of sight mission, the camera angle must be set at 0o (tap on Set to 0o).
The following parameters can be adjusted.
* Recommended value is based on a 2m radius structure. If the structure is wider, then the radius should be increased accordingly.
Manual images mission
The Manual images mission is meant to control the drone with the remote controller and take images from custom points of view.
Special workaround for Guyed towers
Designing the right flight plan for Guyed towers can be a bit tricky due to the cables holding the tower to the ground.
The right flight plan for this kind of structure is based on a single Orbit mission on top of the tower with a camera angle between -40o and -35o, and a minimum of eight Single Vertical missions (usually nine Single Vertical missions, three on each space between cables) and always avoiding the cables. Both the Orbit mission and all the Single Verticals should always have the same radius (recommended value 8m).
