Before You Start
We are currently trialling capture strategies tailored to rooftop antennas. Participation in the trials is by invitation only and limited to pilots who are experienced in using Scanlink for SiteSee. By participating in this trial, you acknowledge that you do so at your own risk. If you are interested in participating in the trials, please contact support@sitesee.io.

Scope of this Guide
This guide is based on the document Automatic Image Acquisition With Scanlink and only describes those aspects of the rooftop antenna capture that differ from a standard tower capture with Scanlink. For additional information (e.g. on safety and risk management, equipment requirements, when to fly, using the in-flight controls, etc.), please refer to the latter.

Capture Components
Capture Procedure
    Step 1 - Set Camera Exposure
    Step 2 - Perform the Roof Antenna Captures
          Setting Focus
          Marking
    Step 3 - Perform the Roof Capture
Pausing or Cancelling a Mission
Resuming a Mission

Capture Components

A rooftop capture consists of two missions types:

1. Roof antenna capture
2. Roof capture

The roof antenna capture involves an overview orbit of the antenna captured with the gimbal at -45 degrees, as well as one orbit per RAD captured with the gimbal at -30 degrees. The orbit radii are about 8 m (26 ft). If there are several antennas, this mission must be performed for each of them.

The roof capture combines an orbit around the roof captured 15 m (50 ft) from the roof periphery and 15 m (50 ft) above it with a grid scan of the roof area captured 10 m (33 ft) above the antenna top.

Capture Procedure

Planning and flying a rooftop capture consists of the following steps:

1. Set camera exposure
2. Perform the roof antenna captures
3. Perform the roof capture

These steps are described below in the order they must be performed.

Batteries Charged?
Ensure the batteries of all equipment (drone, remote controller, and tablet PC) are charged sufficiently to fly your missions (full charge is recommended).

Camera Lens Clean?
Ensure that the lens of your camera is clean. A dirty lens can result in an unusable image set. Rain droplets and condensation can also be a problem. Condensation can result when taking the drone out of an air conditioned car in humid weather. In this situation, allow the drone to acclimatise for about 15 minutes before flying.

Step 1 - Set Camera Exposure

Avoid Incorrect Camera Settings
Incorrect camera settings are a frequent cause of capture issues and result in low-quality, often unusable image sets. So please make sure you strictly adhere to the instructions below. Check your settings prior to launching each flight and after resuming a mission, and do not change them while flying the missions.

Constant Exposure Settings Required
Only set manual exposure once prior to starting a mission. Use the same fixed settings for the whole mission (i.e. site overview orbit, structure scan and RAD scan), that is, do not change either ISO, aperture or shutter speed while the mission is in progress.

High Contrast Situations
Especially on sunny days and when the sun is low, the side of the tower exposed to the sun is much brighter than its shady side. The procedure below uses the histogram to help you capture images that are neither too dark on the tower’s dark side nor too bright on its bright side. For background information on what a histogram is and how to use it, please consult this page.

1. Tap on the pink button displaying your drone model . This opens the following screen (tap  to return to the task list):
   
   
2. For the following steps you will need the histogram. If it is not displayed, tap >  and turn on the Histogram:
   
   
   
   
3. If the histogram is placed inconveniently, you can drag it to a more convenient position.
4. Place your drone on a white sheet of paper as shown below (to avoid reflections, do not use glossy or laminated paper). Ensure that the paper is flat on the ground and exposed to as much ambient light as possible. If the sun is shining, make sure the paper is in full sun and neither the drone nor anything else cast a shadow on it.
   
   
   
   
5. Use your remote controller to adjust the gimbal angle downward until the paper completely fills the screen.
6. Tap , then select manual exposure mode M and adjust the ISO to 100 and aperture to F4.
7. Adjust the Shutter speed until you see a single sharp peak approximately in the middle of the histogram. This peak represents the current exposure of the white paper.
8. Slowly decrease the shutter speed in single steps and watch how this histogram peak moves to the right as you do so. Stop when the peak has nearly reached the right margin of the histogram and no longer moves when you further decrease the shutter speed (see screenshot below).
   
   
   
   Here some examples of correct and incorrect exposure settings:
   
   
   
   
9. Check the brightest parts of your tower (tower pole, antenna panels, dishes, etc.). If they are significantly darker than your sheet of paper (e.g. painted grey or green), reduce the shutter speed by a another stop (for example in the screenshot above from 1/80 to 1/60).
10. Exposure is now set correctly. Tap  again to close the exposure settings.

Step 2 - Perform the Roof Antenna Captures

Multiple Antennas
This step must be performed for each antenna. For example, if there are two antennas on the roof, you should have received two tasks named SiteSee Roof Antenna Capture 1 and SiteSee Roof Antenna Capture 2 (or similar). If you don't have enough tasks, please request additional tasks from support@sitesee.io.

Tap to return to the Task list, then tap on a task named SiteSee Roof Antenna Capture. The Dronelink app will load the task. Before tapping 'Get Started' set the focus as explained below.

Setting Focus

Use Manual Focus
SiteSee requires its pilots to adjust focus manually using the procedure outlined below. The focus must be set for the first roof antenna capture as well as when resuming a paused mission after the drone was turned off (e.g. to swap batteries).

The following procedure sets focus to a distance of approximately 15 m (50 ft). This distance is used because due to the depth of field achieved with apertures of F4 and above it will result in sharp images from about 3 m (10 ft) to infinity.

1. In the top right corner of the screen, tap to switch to AF (auto-focus).
2. Take off and fly your drone to an altitude of approximately 15 m (50 ft).
3. Set the gimbal to -90 degrees (i.e. pointing straight down).
4. Tap to activate touch focus . On your screen, tap on a section of the ground that is well structured (i.e. easy to focus on). A green square will briefly flash to confirm that focus has been set. If you are unsure that focus was set correctly, repeat this step. Alternatively, instead of using touch focus, you can half-press the shutter button.
5. Tap again to switch to MF (manual focus). Switching back to MF will fix the focus and prevent inadvertent changing of the focus while the mission is in progress (e.g. by accidentally touching the screen).

Focus Peaking
To help you verify that you have set focus correctly, you may want to use focus peaking. This feature works by showing red contour lines around the objects that are in focus. To turn on focus peaking, tap > > Peaking Threshold > High.

Marking

You are now ready to start the task. Tap on the 'Get Started' button. Scanlink will guide you through marking the antenna location and its dimensions. Please read and follow the step-by-step in-app instructions carefully. During this stage, you will also be able to enter obstacles.

How to Mark
To avoid inaccurate results when marking the tower dimensions, neither fly too close to it (which could result in inaccuracies due to GPS interference) nor too far from it. A distance of about 8 m (26 ft) to 10 m (33 ft) is ideal. Take care to do all marking as precisely as possible. When marking the Edge of Tower, it is better to overestimate rather than underestimate its radius from the tower centre.

Stick Sensitivity
You may find it easier to mark the tower accurately after reducing your remote controller's stick sensitivity. Use the DJI Go app to reduce stick sensitivity. Tap > > EXP, then reduce the value of Forward/Right from 0.4 (default) to 0.1.

When you have finished marking, Scanlink will show an input summary. Tap 'Continue'. You are now ready to start capturing. To start the mission, tap .

Step 3 - Perform the Roof Capture

Tap to return to the Task list, then tap on the task named SiteSee Roof Capture. The Dronelink app will load the task. Unlike the antenna capture, this task uses autofocus instead of manual focus, so there is no need to set focus. When performing this task, you can take off anywhere you like (i.e. it is not necessary to land the drone next to the antenna base). Please read and follow the step-by-step in-app instructions carefully.

Important
To avoid focus issues, always perform this step after capturing all antennas. 

Pausing or Cancelling a Mission

Occasionally, it may be necessary to pause or cancel a mission, for example, to change batteries or if the drone gets too close to an obstacle.

Emergency
To immediately cancel a mission in an emergency situation, switch the flight mode on your remote controller from P to S or A. You will then be able to control the drone with your joysticks.

A mission in progress can be paused by tapping (see screenshot below). Once paused, the mission can be cancelled by tapping . Once a mission is paused or cancelled, the drone can be controlled with the joysticks.

Resuming a Mission

Before Resuming
When resuming a mission, the drone might fly straight to the point where the mission was interrupted. Therefore, to avoid collision with obstacles, ensure that no obstacles are between the drone and the point where the mission was interrupted. If necessary, take off and fly the drone manually near the resume point before resuming.

Check Exposure Settings
Before resuming a mission, check that the camera is still in manual exposure mode and that the exposure settings have not been changed accidentally. The current settings are displayed at the top right of the screen. You can also tap to check.

To resume a paused mission, tap . To resume a cancelled mission, tap to return to the Tasks list, then tap the cancelled task, then tap .

Re-Centering Before Resuming
The in-app instructions recommend re-centering the tower before resuming the mission. In our experience this is usually not necessary. To save time, we recommend you resume without re-centering. Re-centre only if the drone does not rejoin the flight path accurately. To do so, pause the mission, then resume it again and follow the in-app instructions to re-centre.

Roof Antenna Captures Only
If you turned off your drone (e.g. to swap batteries), you must adjust manual focus again as described in Step 2 above before resuming the mission.