How to scan cell towers - PIX4Dscan

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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.

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

 
Important: Acquired images must be suitable to generate a good quality 3D model. Optimally reconstructed antennas will ensure good results at the post-processing stage (antenna recognition and measurements).

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.

Pix4Dscan_point_cloud.JPG

Left: Noisy 3D model.                       Center: Low-density 3D model.        Right: (Required) High-quality 3D model.

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:

  1. One Helix per tower structure if there are no obstacles around the tower (orange).
  2. One Underneath Orbit per antenna nest to get high-quality images from the lower side of the antennas, connection board, etc, (blue).

Or: 

  1. 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.
  2. One Orbit per antenna nest (green).
  3. One Underneath Orbit per antenna nest to get high-quality images from the lower side of the antennas, connection board, etc, (blue).

                ILL_INS_Pix4Dscan_Flight_Strategy_1.jpgILL_INS_Pix4Dscan_Flight_Strategy_2.jpg

Setting references

The Cell Tower asset locations are based on some references recorded by the operator after taking-off and while piloting manually the drone in the air.

 
Important: PIX4Dscan does not use the base map for cell tower mission planning. In order to correctly position the mission, characteristic points, for example, the center of the cell tower, need to be identified while flying the drone with the remote controller. The mission is then created using the measured position of these characteristic points.

After tapping the Cell Tower asset mission in the project creation window, follow the onboarding guide and determine 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. 

 
Important: This step is shown if the drone take-off position isn't at the same elevation as the lowest point of the cell tower upon user confirmation. 

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°.
  • Point the camera at the base of the tower.
  • Tap on Next to confirm the current tower lowest point reference.

                                                    ILL_INS_Pix4Dscan_Cell_tower_lowest_point.jpg

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°.
  • Point the camera at the center of the tower.
  • Tap on Next to confirm the current tower center reference.
  ILL_INS_Pix4DscanPix4Dscan_Cell_tower_center.jpg

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.

 
Note: Keep in mind that all height values are relative to the drone take-off position. For security reasons, ensure to take-off at the same level as the tower base or to set the tower lowest point reference accurately.

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°.
  • Point the camera at the top of the tower.
  • Tap Next to confirm the current tower highest point reference.
  ILL_INS_Pix4DscanPix4Dscan_Cell_tower_highest_point.jpg

Cell tower project panel

When the cell tower references have been set, the project panel is displayed. It is divided into 3D Model and Visual inspection categories containing all the missions to efficiently reconstruct and inspect cell tower assets.

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 project panel 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 project panel by tapping on the cross cancel.pngat the top right side.

Cell_tower_project_panel.PNG

Signal loss scenarios

The PIX4Dscan 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) loading 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

 
Note: The above exposure compensation values (EV) are reference values, but can be modified within their ranges to adapt to the luminosity of the images.

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 PIX4Dscan while performing a mission.

3D Model missions

No obstacles around the cell tower:

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.

  ILL_INS_Pix4DscanPix4Dscan_Helix_mission.jpg

The following parameters can be adjusted.

Parameter Description Recommended value
Mission min-height

Height of the helix base

12m
Mission Radius

2D distance from the helix to the cell tower center position

8m
Overlap

Overlap level between images

Optimal

 

 
Note: Even though a well-performed Helix Mission will give you a full 3D reconstruction of the tower and antenna recognition, it is recommended to also perform an Underneath Orbit mission per antenna nest if you need high-quality images from the underside of the antennas, connection board, cables, etc.

 

With obstacles around the cell tower:

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 antennas.

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.

  ILL_INS_Pix4DscanPix4Dscan_Orbit_missionV2.jpg

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.

Parameter Description Recommended value
Capture mode**

Time interval capture: time optimized continuous flow

Stop at capture point: stability and image centering optimized flow

Time interval capture
Flight direction

Flight direction allows users to define the direction of a circular mission 

Clockwise or Counterclockwise
Truncate by

Mission truncation allows users to define a truncation angle for the mission, providing flexibility in mission design

Default: 0°, Range: 0° - 315°, Steps: 15°
Images The number of images that will be taken along the orbit 80 images
Camera angle Camera angle at which the images are taken -40º to -35º(min -60º, max -30º)
Height Orbit height relative to the take-off point Based on drone position and depending on the POI height
Radius 2D distance from the orbit to the cell tower center position 8 m. Based on drone position*

* 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. 

  ILL_INS_Pix4DscanPix4Dscan_Cylinder_mission.jpg

 

The following parameters can be adjusted.

Parameter Description Recommended value
Flight direction Flight direction allows users to define the direction of a circular mission Clockwise or Counterclockwise
Truncate by Mission truncation allows users to define a truncation angle for the mission, providing flexibility in mission design Default: 0°, Range: 0° - 315°, Steps: 45°
Mission min height Height of the cylinder base 15 m (min. 5m above min POI height)
Mission radius 2D distance from the cylinder to the cell tower center position* 8m
Verticals The number of vertical lines of the cylinder 8
Front overlap The image front overlap in the vertical line 75%

 

* 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.

  ILL_INS_Pix4DscanPix4Dscan_Single_vertical.jpg

The following parameters can be adjusted.

Parameter Description Recommended value
Mission min height Height of the vertical line base 15 m (min. 5m above min POI height)
Mission radius 2D distance from the vertical line to the cell tower center position 8m*
Front overlap Frontal overlap between images in the vertical line 75%
Flight direction Trajectory of the drone along the single vertical Up to down

* If multiple Single vertical missions are performed, it is recommended to use the same radius.

 
Note: We recommend a minimum of 8 verticals per project to ensure a good reconstruction.

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.

  ILL_INS_Pix4DscanPix4Dscan_Underneath_orbit_copy.jpg

The following parameters can be adjusted.

Parameter Description Recommended value
Flight direction Flight direction allows users to define the direction of a circular mission Clockwise or Counterclockwise
Truncate by Mission truncation allows users to define a truncation angle for the mission, providing flexibility in mission design Default: 0°, Range: 0° - 315°, Steps: 15°
Images The number of images that will be taken along the orbit 16 images
Radius 2D distance from the orbit to the cell tower center position 8 m
Height Orbit height relative to the take-off point Based on drone position, and depending on the POI height
Camera angle Camera angle at which the images are taken 25º (min 0, max 30º)

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 away from the asset.

In order to start an Orbit line of sight mission, the camera angle must be set at 0º.

  ILL_INS_Pix4DscanPix4Dscan_Orbit_line_of_sight.jpg

The following parameters can be adjusted.

Parameter Description Recommended value
Flight direction Flight direction allows users to define the direction of a circular mission Clockwise or Counterclockwise
Truncate by Mission truncation allows users to define a truncation angle for the mission, providing flexibility in mission design Default: 0°, Range: 0° - 315°, Steps: 15°
Images The number of images that will be taken along the orbit Default: 8, Range: 8 - 32, Steps: 1
Radius 2D distance from the orbit to the cell tower center position 8m. Based on Drone position*
Height Orbit height relative to the take-off point Based on drone position and depending on the POI height

* 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.

  ILL_INS_Pix4DscanPix4Dscan_Manual_images.jpg

                                                 

 

 

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3 comments

  • Fernando Luís

    The image Underneath orbit sub-mission, similar to the one orbit sub-misson, should have the values used in the example printed in the image (Altitude, Radius, Gimble). Allitude is missing.

     

     

     

     

  • Tomas Bechmann

    I had issues with GPS signal and had to make the radius 18 meters to avoid fall outs. Any issues with a larger radius except for resolution? Any clever tricks to avoid it?

  • Marco Paccagnella

    Dear Thomas,

    Depending on the drone location, some satellites can be physically hidden leading to a poor GPS signal. Could you eventually try to start the mission in a different location around the cell tower?

    We usually recommend a radius of around 8 meters. A larger value would lead to lower details in the images. Please keep the radius as constant as possible in the different cell tower sub-missions to get a good reconstruction.

    I hope this helps.

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