What does a good workflow look like?
The drone is an excellent tool to have in your surveying arsenal, but it is not the right tool for every job. At the beginning of every project we decide how we are going to execute our data collection, whether it be with the drone, or traditionally. Determining the effectiveness of the drone for your specific job will be pertinent to your success and overall satisfaction with your drone. So how do we make the decision on whether or not to use our drone? For all examples here we will reference the Phantom 4 Pro.
It is important to set realistic expectations for the drone, the first and most all encompassing is that the drone can only map what it can see. It is equipped with a 20MP camera which is its data collection apparatus. So naturally, if the camera cannot see it, it cannot collect the data. The biggest consideration when deciding if it will be worthwhile to use the drone or not is the type of ground cover at the job site. If there are trees, or extensive ground cover, such as brush or shrubs, the drone will not be able to accurately map the earth's surface. For a site that has extensive ground cover, traditional land surveying methods will be more effective.
Another factor will be airspace. Is your site located within 5-10 miles of an airport? If so, we have to check the airspace and deal with it accordingly. If the area we plan to fly in is within a mile of an airport, there is a chance there will be a 0 foot ceiling and it can be difficult to get authorization to fly over that site, and alternate plans should be made in case that happens.
Additionally, you need to consider what type of area you are flying over; if it is rural or industrial, that’s usually a full on green light; and you are good to go. But if the site in question is in a heavily publicly trafficked area, such as a school, shopping center, or even neighborhood, you have to operate with discretion, and not during peak hours of business to mitigate risk to people on the ground.
It is also important to have realistic expectations for the accuracy of the data. We can map drone data to .1’ accuracy, given certain conditions, one of the most important, being the quality of targets used for GCPs, which is discussed in the “Ground Control” section. Low image resolution and bad lighting can contribute to loss of accuracy. That being said, the value of the drone increases as site size increases. Some small sites will be better shot on the ground, especially if you need accuracy better than .1’. Large sites are where you will really see some serious time saving. The drone is a broad paint brush, which can do 90% of the work for you, but there will always be things you as surveyors need to verify in the field and shoot traditionally.
There are also limitations to what the drone can discern. For example; the drone has a hard time picking up front of curb and thus will be an ineffective tool if that is the main feature you are after.
So now we have decided that the drone is the best tool for the job at hand. We have a site, a mission date, and are ready to continue with our planning. Throughout the weeks or days before your mission, you should keep an eye on the weather; are there going to be any visibility issues? (you need to be able to see the drone, so low visibility may make it unsafe to fly) Wind issues? (The phantom 4 pro can only fly 30 mph at top speed, so if the winds are gusting more than 30mph, your drone will not make progress in that direction. It is a good rule of thumb to reconsider flights if there is a wind over 15mph) Temperature issues? ( the Phantom 4 pro should not be operated below 32 degrees Fahrenheit due to the unpredictable nature of lithium batteries in cold weather, on the contrary, the drone should not be operated above 105 degrees fahrenheit as this is also unsafe for the batteries, overheated batteries can fail and even combust, causing mission loss and increasing risk of damage to persons and property) And last but not least; is it going to rain or snow? The phantom 4 does not do well in precipitation, and neither would your camera and photos. If there is a chance for precipitation when your flight is scheduled, be sure to make alternate plans.
At some point prior to the day of the flight, we need to plan our mission in the autopilot software as well. There are a few softwares out there for this, we like Map Pilot by Maps Made Easy, so for our purposes we will use it in this example.
When planning your mission in flight planning software, be sure to first and foremost set your flight pattern to completely envelope the area you need data on, and especially your GCPs. It is a good rule of thumb to push your flight lines out one extra line than you think you will need. This can add about 5 minutes to a mission but can save you hours and even days if you have too little data and have to re fly the site. It is at this time that you will select your flight height, taking into consideration all of the obstacles or airspace that you may encounter on the site. Once you have the height selected, you can then see how many batteries you are going to need. It is always a good idea to charge an extra 1 or 2 batteries to give yourself a buffer should any delays occur. Be sure to save your planned mission for offline use, as you will be flying (most likely) in an area without WiFi coverage.
Now it is the day before the flight, there are a few good habits to get into for day before mission planning. As always continue to check the weather and solar data to make sure you have ample satellite coverage and there are no surprise storms coming! Also, check your flight restrictions again, including airspace, to be sure no temporary flight restrictions (TFRs) have been issued since you last checked. Next, it’s a good idea to verify with the client that they know you will be flying tomorrow, and to notify all necessary parties of the drone activity to be conducted. You also want to double check your equipment and make sure everything is charged up and packed away, ready to go so you don’t forget anything. This ensures that your kit is always stocked in case the equipment was not put back correctly the last time and serves to prevent any unexpected delays due to lack of equipment at hand.
PRE FLIGHT PREPARATIONS (in the field)
It is now the day of the flight. You have packed up all of your equipment and headed out to the site. When you get out to the site there are some regulatory and safety measures you have to take. First being to notify any and all persons at the site that we are going to be conducting drone operations over-head, that being any persons in the direct vicinity, or people who are clearly not going anywhere and will be flown over, it is not necessary to stop a guy riding his bike across the flight path to notify him.
Next, we will check the flight area visually once more to confirm that we have accounted for all obstacles on the site and ensure that nothing has changed since our last visit.
Once this is complete we have to identify a takeoff and landing zone. Ideally, this zone should be in a place free of overhead and lateral obstruction, ideally not in tall grass or debris, as the gimbal and camera can get caught on debris during its preflight calibration and damage it.
Once the takeoff and landing zones have been established, the wind speed, temperature and visibility should be verified one more time to make sure we fly within established aircraft safety parameters.
Before we take off, we need to conduct a Visual inspection of the aircraft. This is an important risk mitigation step, checking for damage prior to flight guarantees that at least you won’t take off with a malfunctioning component giving your flight success likelihood a healthy boost. Starting with the hull of the aircraft, follow the seam in the middle around the vertical axis of the drone all the way out to the arms. Check to make sure the two plastic cowls are aligned; misalignment is an indicator that the drone was put under a good amount of stress and should be inspected closer. Check the skids to make sure they are sturdy and well connected to the drone.
Next check each propeller by running your fingers from the base of the propeller to the tips, checking for any chips, or cracks. Take the tips of each propeller in your fingers and gently twist; this will show any cracks in the propeller that may have been invisible prior. The propellers and motors are what keep the drone in the air, if there are issues with either, flight should not commence until repairs have been made.
Next are the motors. You’ll want to make sure each motor bell is free moving and free of any dents or dings. Dents or dings are indicators that the aircraft has been struck; that force can disrupt sensitive magnets on the inside of the motor bell. If you see any dents, proceed with extreme caution, as motor failure almost always results in catastrophic failure and best case scenario, some equipment damage. Debris from the drone being in a workshop or just out in a dusty environment can get inside the motor bells and cause engine issues. Blowing air into the bell with your mouth is plenty of air to clear any debris that might be in the motor bell. Using an air compressor can damage the sensitive apparatus, so it is best to avoid them.
The only component left to check is the camera and gimbal. Check to make sure the camera lens is clean; after all, this is the money maker, without good pictures, we wont get good data! The lens should not be touched and if it needs to be cleaned, be very careful and use a microfiber cloth. The same goes for the gimbal. Gently examine the gimbal to make sure it is free of obstruction and able to operate normally. While rare, gimbal failure can compromise a mission. Preflight inspection is absolutely essential, but is definitely not the only time these checks can be done. In fact, checking these physical parts on a regular basis is good practice.
Next, we will pre flight the controller. Be sure the antennae are extended and if applicable, the tablet is connected to the controller, be sure the stick controls are free moving.
Next we check the batteries. Start by checking the charge of the battery, your batteries should be fully charged before using. Next inspect the battery vents; you should be able to see clear through them if all's right with the battery. Not being able to see through the battery is an indication that something is wrong. It is important that these vents stay clear, as the battery needs to be cooled properly to work optimally, blow through the battery to clear any debris that might have collected, if this doesn’t clear the vents, the battery should not be used.
If the battery passes inspection, record the battery ID number in a battery log. Batteries should be labeled for the purpose of identifying faulty equipment, and for properly cycling battery use. Batteries have a finite lifespan and should be cycled in rotation to ensure they all age consistently. If cycled correctly, the batteries should last for up to 2 years of regular use. Logging battery flight info allows for easy tracking of battery lifetime use.
Now that the battery has passed inspection, it is time to discuss the flight plan with all participants, be it co workers, clients or other persons involved in the operations. This check in will make sure everyone is on the same page and is ready for the mission to begin.
Now it’s time to insert the battery into the aircraft and power on in order, our controller, aircraft, and (if applicable) tablet. The green light on the controller indicates a connection with the aircraft, and flashing green lights on the aircraft indicate a connection to the drone. When the tablet is connected, the Ipad should indicate that it is charging; set the controller setting to “P”; now open the DJI GO app and enter aircraft. Check the overall status bar in the upper left hand of the screen, if it is green, you are good to go! If it is red or yellow, simply tap the bar to get a more detailed description of the issue. While still in the DJI Go 4 app, verify that your SD card on board the aircraft has sufficient space to take pictures for your project.
At this point, if you are going to fly the drone manually you are cleared for takeoff, only in rare cases will you be flying manually for data collection. For automated flight, there are a few more things we need to do.
Close the DJI go app and open the autopilot app. From there you are going to select the desired mission and upload it to the aircraft. After that you want to ensure the altitude is sufficient for flight, do a last scan of the site to make sure you are cleared of any obstacles, and verify the drones location on the map. And away you go.
Throughout the mission you will want to keep an eye on the drone at all times, and verify that it is flying the mission correctly. Be sure not to bump the camera angle button/dial on the top of the controller, this will change the angle of your photos and make them more difficult to process. Make sure the drone returns to you after each 17 minute flight to change the battery out. Once you change the battery out, continue the mission and the drone should start right back where it stopped. Upon completion of the mission, be sure to record your flight time and power everything off and pack up accordingly.
We have developed a checklist which serves to make sure you leave no stone un-turned when it comes to ensuring you are ready for your mission. Filling in the mission date, location, aircraft ID (FAA registration number) and Job number, as well as the name of the pilot, will help you track your flight time and cycle batteries properly to ensure their longevity. This checklist should be treated as an essential tool and is fundamental in guaranteeing good data collection and safe operation overall, if you cannot satisfy one of the items on the checklist, you should seriously reconsider flying that site, it may be best to wait for a better day or more conducive circumstances. The checklists can be downloaded below.