AERO RANGER FORUM

PILOT SUPPORT

User avatar
BY admin
#26
Image

Linear Scan missions are part of the family of Survey type missions, with the output typically used to create maps using online services such as our built in Maps Direct service. It is similar in many ways to the Survey Mission, but has been rotated on its axis to be vertically oriented. The linear scan mission is mainly used for surveying large flat vertical structures such as the walls of large buildings, mine pit walls, and dam walls or even steep hills.

NOTE: If you have a Spark you cannot use this mission. The Spark does not support waypoint missions.

A linear scan mission uses a back and forth "lawnmower" pattern to map the structure, but this is oriented vertically, with the strips running horizontally. The aircraft is flying sideways for most of the mission, with the camera pointed at the structure.

The mission starts at the above the upper specified altitude (to look down) and works downwards to the lowest specified altitude.

Unlike a survey mission, the gimbal must point downwards to avoid capturing too much sky. Typically, the gimbal angle starts at 45 degrees downwards, and tilts more horizontal as the drone descends.

Tip: Linear Scan is not recommended for low structures such as residential house walls, because of the risks of flying at very low altitude and the small size of a house.

Tip: Bridges may prove difficult to survey due to their construction (typically made of many of thin structures) and proximity to water. Thin structures and lots of background in each image will confuse stitching algorithms

Four steps are required to produce a linear scan mission:
  1. Setting the mission objectives
  2. Define the survey area
  3. Define the upper and lower flight altitudes
First, navigate to the Plan screen using the main menu as shown below. Tap the "Hamburger" icon at the top left of the screen to display this menu:

Image

On the Plan screen, move the map close to the area that you would like to survey and zoom in to a comfortable level. Don't zoom in too far. While you can zoom and scroll later, it is easier to move the map to roughly where you need it first.

When ready to create the mission, press the round blue + button at the bottom right of the screen to reveal the mission selector. Tap on the "Linear scan" item and tap Next to start building a Linear Scan mission.

Image

Step 1: Mission Objectives

Note that you can exit mission creation by tapping the X at the top left of the objectives dialog. This will cancel the operation, leaving the previously loaded plan as the active one.

The linear scan mission objects are as shown below

Image

In the example above, there are several important settings that you can change, but in many cases the defaults will be suitable
  • Camera - The camera should show the drone that you are connected to now, or were last connected to.
    • Tap on this section of the dialog to display the camera settings.
    • In survey missions, only JPG photos or video can be taken due to the short time between shots that is required. The camera will default to JPG even if you select RAW.
Tip: You don't have to change Camera settings now, you can change them at any time prior to takeoff. Camera settings are available from the main app menu
  • Min Safe Alt - this is a critical setting for the entire mission.
    • Whatever other settings you choose, no part of the mission can be lower than this altitude.
    • It also defines the altitude at which the vertical part of takeoff finishes and the vertical part of landing begins
    • Make sure the Min Safe Alt is set well above any obstacles such as tall trees or buildings in your area of operations. The safety of the drone and people and property around you is your responsibility.
    • Remember - all altitudes are measured relative to the Home point.
  • Sidelap % - The sidelap % defines the overlap between each of the photos that the aircraft will fly.
    • Given the aircraft is flying sideways for linear scan missions, this has the same effect as the the overlap setting in a survey mission.
    • The higher this value, the more photos will be taken. This can vary from 40% to 95%. 70% is a good default for most work.
  • Overlap % - This affects the vertical distance between the horizontal flight lines, based on the camera properties and distance from the structure you fly. This can vary from 40% to 95%. 70% is a good default for most survey work.
  • Target Speed - this is the speed in m/s that the aircraft will attempt to attain when flying the mission
    • If you set this too fast, you will be warned that the camera will not be able to keep up - either reduce the sidelap % or reduce the speed. If you do not, the software will automatically set a lower speed.
    • If you set this too fast, you may not have time to react in case of an incident where you need to take manual control.
    • 5m/s=18km/hr=11.2 miles/hr
  • Gimbal Angle - Sets the initial gimbal angle (0=horizontal, 90=straight down).
    • In most cases linear scan missions require an initial 45 degree down angle, but you may change it here.
    • The angle will gradually be reduced (become more horizontal) as the drone flies lower through the mission.
    • You will not have manual gimbal control during flight, so select the correct angle here.
  • Review mission after creation - if you tick this, the app will remain on the Planning page once you have finished creating the mission, if ticked off, it will automatically return to the Fly page, ready for takeoff.
When you are satisfied with the settings, press NEXT at the top right of the screen

Step 2: Define the structure to be scanned

Image

In step 2, the task is to define
  • The location and extent of the linear structure you want to survey
  • The offset distance from this structure that the drone will fly at
Tap once on the map, a green waypoint icon will appear. Tap again and a second green waypoint will appear. You can drag these into position over the structure of interest.

Note: You are defining the structures location here, not the path that the drone will fly.

Once you have two waypoint icons, you can drag the aircraft in or out to set the distance from the structure that it will fly. You can even flip the aircraft to the other side of the structure by dragging the icon there.

The distance offset is very similar to the altitude control in a standard survey mission. It controls how many images will be taken and the resolution that will be achieved in each one

Tip: To zoom in/out and move or rotate the map, you can use regular pinch/zoom or single finger drag gestures on an area of the map away from the linear scan widget. 

Tip: If you have zoomed in too far, finger gestures may not work correctly. In this case, use the  Image button at the top right of the screen to zoom out one step.

When you are satisfied with the location, press the blue OK button

Step 3: Upper and Lower flight altitude

The final stage of linear scan mission creation is to define the upper and lower range

Image

The dialog above will appear. Two values are required
  • The estimated structure height
  • The lowest scan height
Tap on the text boxes to pop up the keyboard and enter values.

Est Structure Height (m)

The estimated structure height is your best estimate of the altitude of the top of the structure.
  • This altitude is relative to the Home (takeoff) point, not necessarily the base of the structure (unless you takeoff from there)
  • The software will use this to locate the first strip.
  • The actual aircraft altitude in the first strip will be above this to ensure it can look down at 45 degrees (or the gimbal angle set in step 1) to cover the top of the structure.
  • Can't be above the legal operating altitude of 122m
Lowest Scan Alt (m)

The lowest scan altitude is where the last strip will be located.
  • This must be above the Min Safe Alt (you will not be able to enter a lower number)
  • The number and height of strips in between the upper altitude and lower altitude will be calculated based on the camera properties and offset distance from the structure.
Once you are satisfied with these settings, press FINISH, the mission will be created as shown below

Image

The waypoints that are created follow the structure, but at the offset you specified in step 2, in case you are wondering why they differ from the points you placed in that step.


Mission Statistics
After the mission is created, basic mission statistics are updated in the white strip beneath the map.

In the above case, the mission is 1.49km long, 61 pictures (estimated), 6:16 mins flight time (estimated), 3.1cm per pixel

Final tips for Linear Scan missions:
  • You can only fly a Linear Scan mission with the camera set to JPG or Video. RAW mode does not work due to the short time between images that is required during surveying flights. RAW images cannot be taken any faster than once every 10secs. If you select RAW (dng), the camera will automatically switch back to JPG mode.
  • This camera gimbal angle is managed by the drone based on your settings in step 1. You won't have manual control over the gimbal during a Linear Scan mission.
  • The drone does not take terrain into account in any mission type. All altitudes are relative to the takeoff point. Please ensure you set the Min Safe Alt high enough to avoid crashing into terrain, buildings, people or infrastructure at any point of the mission. You are responsible for the safety of your equipment and people and property around you.
You are now ready to go and fly the mission, return to the Fly page of the app
WHAT IS THE HOME POINT?

A critical part of any mission is the Home point.

SUPPORTED DRONE MODELS

Most recent DJI drone models are supported

HOW DO I CHANGE CAMERA SETTINGS?

Camera setting have recently had a major revamp.

How do I zoom the camera

To zoom your camera using AeroRanger

TRY OUT AERORANGER