DJI Phantom 4 Pro Yaw Drift

Phantom 4 Pro Yaw Drift

Compensate P4P Yaw Drift

What causes the Phantom 4 Pro to drift in yaw (heading) during programmed flights? This appears to be a common thread in a number of blogs and is a problem we’ve also encountered. As you know, I like to take on the hard problems, think them through and develop solutions. In this blog, I’ll offer ways to measure the offset and a method of compensation.

As I stated above, this is a common problem, but no one that I know of has determined the cause. Please comment if you have a better explanation and I’ll update this blog.

Are other aerial drones similarly affected? Please comment, I’d love to hear from you.

We See Yaw Drift in All of Our Programmed Flights

The yaw drift that we’ve encountered with our Phantom 4 Pro V2 is much more significant than crabbing (please see our April 28, 2019 blog on crabbing). Our data files indicated that the crabbing effect is around ±1.5 degrees, and is largely compensated by the drone’s flight controller. However, our measured yaw offset runs as high as 30 degrees, sometimes more.

Of note, from our data files we plotted the GPS position, which showed the drone stayed on its programmed circular path and its heading was tangent to the circle.

Measuring Yaw Offset

We program almost all of our aerial drone photography sessions, so when the drone’s camera offsets then it’s pretty obvious in the recorded video. A simple method to measure yaw drift is to record a Point of Interest video. That is, to run a circle around a point with the camera pointed at the center. A large radius allows the drone to be operated at maximum speed (we used 1000 feet radius and 21 mph in our test runs), where the drift was quite noticeable.

For example, print out a Google Map of the test site; then graph the video’s centerline of sight at 15-second intervals. You can measure the yaw offset with a ruler for distance, and a protractor for angle. E.g. measure the distance/angle from the centerline to the center point.

Graphical Data Results

Our data set included ten video runs, taken on different days so we had variations in drone speed, wind speed, and wind direction. In almost every case, the yaw drift was affected by both the drone speed and wind speed. One key measurement was the combined speed of the drone, where we found correlation between the maximum yaw drift and the combined air speed of the drone (that is, heading into the wind).

Our graphical analysis suggests that yaw drift can be minimized when both the wind speed and drone speed are less than 10 mph.

Conditions

  1. Drone: a 2-year old DJI Phantom 4 Pro V2 with an iPad 9.7-inch tablet. Yaw effects were similar for both DJI Go 4 and Litchi apps.
  2. Yaw drift appeared to be the same before and after INS and compass calibrations.
  3. We tried to force the drone’s yaw drift by hovering 5 feet above ground and blowing the drone with a fan. We blew the drone so hard that the camera’s gimbal was pushed into its stops, but it returned to linear after the wind was reduced. The drone’s airframe did tilt into the wind to maintain position, as we would expect, but it didn’t change its yaw (heading).
  4. We measured yaw drift in circular “Point of Interest” runs, where the drone’s camera was pointed toward the center and the drone airframe was flying sideways into the wind. CCW runs resulted in less yaw drift, so only one run was CW.

Conclusions

In flight, it appears that the drone’s flight controller is adjusting heading as the drone tilts into the headwind. So, if there’s a large headwind, the drone tilts more to maintain its GPS speed and it also yaws to the left. Since the drone’s legs don’t appear in the video, we conclude that the flight controller must be changing the drone’s airframe, not the camera.

Minimizing the Effects of Yaw Offset

  1. Fly your drone at a speed of less than 10 mph and when the wind is less than 10 mph.
  2. The yaw offset can be compensated by changing your programmed center point into the wind.
  3. Fly a larger diameter radius so the desired field of view is around 80% of the frame, then crop down to the desired field of view in post-processing.

Short Video Clips

Our post-production services now include short videos to dress up aerial drone video clips that we have taken. This service is ideally suited to real estate firms that want customized information added to their advertising clips.

Our full-service videos include a number of video clips and photos, introduction slides, overhead map photos, closing slides, and audio track options. The difference with our short videos is that only one selected video clip is modified to include an intro slide with agency contact information and an overhead map photo showing property information such as boundaries.

Our short videos are much easier to create and they provide our clients with tailored information in their aerial videos. This information helps your customers visualize the location of the property and area features.

Although we don’t offer moving boundary lines for our videos, we can add them to the overhead map photos (typically credited to Google Maps). Just about any text information can be added to customize the short video to our client’s requirements.

Interested? Please follow this link to a larger example of the above short video:
https://youtu.be/55B2hrF1y9k

Price information is posted to Our Prices tab, under Post-Production. Economies of scale will apply, so if you have several similar short videos in mind, we can discount our price. Please contact us for details.

Drone Take-Down Technologies

Aerial Drone Take-Down

Aerial Drone Take-Down

When small UAV pilots fly in accordance with FAA regulations, they should never have to worry about the technologies in this article. That said, a number of methods have been developed to help the military and law enforcement engage drones that are perceived as a threat. Among them are the technologies stated below. There are probably other technologies as well . . .

As mentioned in my last blog, Remote Identification of Aerial Drones, the FAA will soon require all drones in the U.S. airspace to implement new technologies that will enable identification of the drone and its owner/pilot.

Counter-Drone Technologies Include:

DroneShield offers several models that employ electronic countermeasures (radio frequency methods) to down aerial drones at ranges up to 1.25 miles.
https://www.droneshield.com/

The Dutch firm Delft Dynamics has developed an anti-drone drone called the DroneCatcher. Their medium-sized drone can lock onto a smaller UAV in the air and take it down with a net.
https://dronecatcher.nl/

A ground-based netting system has been developed by the UK firm Open Works that employs a bazooka-like gun to take down a small UAV at ranges up to 330 feet.
https://openworksengineering.com/skywall-patrol/

Lockheed-Martin developed their Athena laser-based air defense system for small targets, which can destroy small aerial drones in flight. Built for military applications, variations of this technology could find their way into domestic law enforcement.
https://www.lockheedmartin.com/en-us/products/athena.html

Drone Defense, a UK company, offers their RF-based system called the Paladyne E1000MP, which disables drone communications. Based on its description on the company’s web site, the targeted drone is kept out of a sensitive area but not taken down.
https://www.dronedefence.co.uk/

Conclusion

The popularity of aerial drones continues to grow, and with it comes the possibility of their unlawful usage. As a result, counter-drone technologies are quickly developing. For now, it seems these technologies are not available to the general public, but are almost certainly finding their way into military installations, prisons, critical infrastructure, and other controlled airspace. Small UAV pilots should be aware of them if their operations take place in or near sensitive areas.

Remote Identification of Aerial Drones

New Rule

New Rule Will Impact Small Aerial Drones

Small aerial drone technology will be changing in the next two to three years as the Federal Aviation Administration (FAA) implements new technologies that will enable tracking of drones in the U.S. airspace.

New Rule Affecting Small Aerial Drones

The FAA is currently developing a new rule that will require remote identification of small unmanned aerial systems (UAS). Upon publication of the final rule, all UAS systems flown in the U.S. will have three years to become compliant. Of note, UAS manufacturers must be compliant within two years.

Under this proposed rule, a system of unmanned air traffic management will be implemented to identify and locate aerial drones and their control stations. Information will be accessible to the FAA, national security agencies, and law enforcement. It may also be made available to the public via a cell phone application.

According to the FAA, this new system will address safety, national security, and law enforcement concerns regarding the further integration of these aircraft into the airspace while also enabling greater operational capabilities.

How Will This New Rule Be Implemented?

All UAS systems will need to be registered with the FAA. Upon take-off, the FAA envisions that the UAS will broadcast its information via RF while the remote controller will transmit information via the Internet. The FAA has specifically excluded ADS-B Out and transponder technologies due to congestion of those spectrums.

Three classes of Rule implementation are envisioned:

  1. Standard Remote Identification: Your drone will self-broadcast via RF and your remote controller will send data via an Internet connection.
  2. Limited Remote Identification: No drone RF broadcast, but the R/C must have an Internet connection. Flights will be restricted to 400 feet visual line of sight from the operator.
  3. No Remote Identification: Your drone must be operated within visual line of sight and within an FAA-recognized identification area. (The FAA will assign these areas to community-based safety organizations.)

An in-flight database is expected to include location and altitude of both the aircraft and the control station. Registered owner name will not be included at this time, but will be made available by the FAA to law enforcement. My understanding is that law enforcement will not be able to use this technology to force the aircraft down. (They have other methods to capture drones.)

Legacy Aerial Drone Systems

After this new rule phases in, operating your drone without updated remote identification capability will limit flights to within your visual line of sight and restrict your operations to an FAA-recognized identification area. Enforcement provisions don’t appear in the Rule, but the teeth may be implemented in changes to the Code of Federal Regulations.

Further information on the FAA’s proposed rule for Remote Identification of Unmanned Aircraft Systems can be found at:  Federal Register/Vol. 84, No. 250/Tuesday, December 31, 2019/Proposed Rules

Precision 3-Dimensional Mapping

Topography Map, May 2020

Topography Map Draped Over the 2-D Map

Precision 3-Dimensional Mapping

Aerial drones are the ideal method for collecting precision aerial mapping information for your land development projects. This is exciting technology and the map products that we deliver are truly breathtaking.

Each project begins with a client-provided map that outlines the site that needs to be surveyed. We enter this information into our drone’s autopilot (a mapping application), which flies the drone and collects the photos. Our typical settings are 90% overlap and 3 cm/pixel, which are further explained in our Orthomosaic Mapping and Photomapping blogs (parts 1 and 2).

We’re very good at photographing and delivering precision map products. As described below, several of these deliverables require specialized software to take full advantage of 3-D mapping. We do not offer professional cartography services, but instead provide these files to professionals who have the specialized software for these types of projects. The free software applications described below are suggested for viewing our products, but are not endorsed by FAD-Photo as suitable for professional-level mapping. We do believe, however, that many users will find them quite useful.

3-D Map Processing

Using our typical settings, the drone takes 18 photos per acre of land. For large sites, where we collect hundreds of photos, each pixel of the surface is examined at 13 or more different angles. Map processing aligns the pixels and assembles them into a 3-D composite model that includes latitude, longitude, and elevation.

Accuracy? Each photo is tagged with its position and altitude, so the composite model’s position is as accurate as the Global Positioning System. Typically, 3-4 meters.

Altitude information is based on the drone’s barometer, which has an accuracy of 3-4 meters. (We covered this specification in our April 23, 2020 blog.) Map deliverables are normalized to sea level.

Image processing is highly complex, so we use a professional mapping service provider. These are the deliverable products you will receive:

Full Color 2-Dimensional Map

This JPG file is a composite map of the photos, which are combined into a single panoramic map. Instead of a traditional scale, such as 10 meters per centimeter (or 100 feet per inch), the map service provides scale in terms of centimeters per pixel (or inches per pixel).

The JPG map doesn’t include position information, but its TIF counterpart (also a deliverable) has position information for each pixel. Use an application, such as the free QGIS software to view.

3-Dimensional Maps

DEM – Although monochrome, the Digital Elevation Model map (a TIF file) includes position and elevation information for each pixel. Special software, such as QGIS, must be used to view. The mapping service also provides a JPG of the DEM map, but this product doesn’t include position information.

Point Cloud – This is a LAS file, developed for LIDAR applications. At first glance, this full-color type of 3-D map appears fuzzy and not very useful. However, with a good viewer, such as the free Fugro Viewer, you can zoom in on the left panel image and view its corresponding 3-D model on the right panel. This is useful for looking at pixels under trees which would otherwise be masked. Of note, the 3-D model can be rotated in any direction with the mouse.

3-D Object Map – This is also a full-color map that can be rotated in any direction with the mouse. It offers a much sharper appearance than the point cloud, but it doesn’t get under the trees. Three files are required: the main 3D.OBJ file, a 3D.JPG file, and a 3D.MTL file. (You can rename the OBJ file, but don’t rename the other two.) You can open this type of map with the Windows 10 Object Viewer, but the free MeshLab viewer allows full 3-D rotation and zoom with the mouse.

Other Deliverable Map Products from FAD-Photo

The map processing report provides details on your map products, including map location, output size in pixels, scale in inches per pixel, overlap report, etc.

Topographical map (traditional contour map), where the user can specify the color scheme and contour intervals. (A postprocessing fee applies.)

Topographical map draped over the panoramic map. Here, the contour intervals are overlaid onto the full-color 2D map. An example is provided above and a larger example appears on our portfolio page. (A postprocessing fee applies.)

Do you have a special application?

Contact us for the solution. We’re experts in drone photography, mapping, and postprocessing services.

Flying Your Aerial Drone Over Water

Flying Over Water

Flying Over Water

Flying your drone at low altitude over water can be hazardous to its health. However, there are times when professional aerial drone photographers and videographers will have to do precisely that. The drones I fly are manufactured by DJI, which discourages flying over water.

DJI Manufacturer Statements Include:

The Vision System requires clear pattern variations, with light conditions greater than 100 lux. Further, they state that users should operate the aircraft with great caution when flying over water or transparent surfaces. And specifically, Vision Positioning may not function properly when the aircraft is flying over water.

What is a Vision System?

Vision systems may use ultrasonic sensors, infrared sensors, and cameras to detect objects in close proximity to the drone. Several drone models use combinations of sensors to accurately hold altitude and to enable object tracking functions.

How does a Vision System work?

Vision systems are used for short range detection and ranging. Ultrasonic-based sensors operate at about 40 kHz and use pulsed sonar techniques to detect the nearest object. Camera-based sensors employ image processing to determine objects that not only include the ground below but also people and moving vehicles.

DJI states their vision systems rely on very sophisticated image processing to detect nearby objects. Two models that I have owned are the Phantom 3 Professional and the Phantom 4 Professional Version 2. Both employ a combination of ultrasonic and camera sensors to determine their altitude above ground.

At low altitude, the fusion algorithm prioritizes the camera sensor above the ultrasonic sensor and the altimeter (barometer). e.g. the drone’s control system maintains a certain altitude that is stabilized by its downlooking camera. The problem with flying over water is that the downlooking camera sees what the human eye will see, including objects below the surface such as the bottom.

When hovering over water (or any other transparent object), the processor may be fooled into thinking the drone is flying too high, so it orders the drone to decrease its altitude. This happens fairly quickly, which risks the drone dropping into the water.

When you Absolutely Must Fly over Water . . .

If you have to fly below 2 meters for a special shot, we recommend that you turn off the Vision System to avoid unstable movements by the drone. DJI recommends that you fly the drone at low speed and stay alert to adjust altitude.

What else could possibly cause Altitude Issues over Water?

Other physical effects could fool the drone’s processor into decreasing altitude, but only one scenario seems to fit. For an ultrasonic sonar sensor, the sensitivity time control could cause a near-water second echo to be larger than the first echo, which would read a higher altitude.

What about Sonar Returns off the Sediment?

Although sound waves can penetrate the air-water interface, the transmission loss is about 99.95% – each way! Remember, the sound has to go back through the water-air interface for another loss of 99.95%. There’s just not enough signal return to fool the sensor.

You can likewise rule out other physical effects because they would lead the processor to read a lower altitude. These include: ground effect on the barometer and the increased sound speed caused by prop wash water vapor. In other words, the processor would be fooled into increasing the drone’s altitude.

Conclusion

Flying your drone at low altitude over water can risk losing your aircraft. If you must fly under these conditions, then turn off the Vision Positioning System, maintain a minimum altitude of 2 meters, and keep a close watch on your drone.

Aerial Drone Altimeter Accuracy Specification

Measuring Your Drone's Altitude

Measuring Your Drone’s Altitude

One of the specifications that you won’t find for your aerial drone is its altimeter accuracy. In fact, if you call the manufacturer’s support staff they won’t be able to provide you with that spec either. Technology behind the common altimeter is consistent across many of the latest airborne vehicles, including drones. In most cases, altimeter inaccuracies are minor, so these instruments serve their purpose well.

However, aerial drones operate much closer to ground than most other aviation vehicles. This is where we as drone pilots might notice a drift in reported altitude throughout our drone’s flight. We’ll explain why this drift occurs and what can be done to compensate for it.

How Does an Altimeter Work?

What we know is that as one goes up in altitude, the air pressure goes down. The relationship between air pressure and altitude is quite predictable, but subject to minor variables such as the gas content and temperature. So, whether the readout is an analog meter or a more sophisticated digital instrument, the altitude is easily converted from the air pressure. Click here for a detailed explanation on how altimeters do this.

Which of These “Minor Variables” Affect My Drone’s Altimeter?

Over the time span of a drone flight, the atmosphere’s gas content, that is Nitrogen, Oxygen, CO2, water vapor, etc., can be treated as fixed. Surface-level barometric pressure changes can also be treated as fixed. That leaves variances in temperature as the most significant contributor to altimeter inaccuracy.

Think about where the barometer is located in your drone. It’s a small sensor mounted on or near the motherboard in a relatively confined space. From the beginning of a flight to its end, heat from the drone’s control circuitry builds up in this space, affecting the barometer. Whether it’s a change in air pressure or temperature, the result is the same – a change in reported altitude.

Low Altitude Operations

This is where the thermal effect on reported altitude is more noticeable. You may have noticed when coming in for a landing that your drone is reporting an altitude of some 15 feet or so when it’s actually 3 feet off the ground. If you were to simply take off and hover, you would find that the indicated altitude slowly increases while the drone is actually in a stationary position. These are thermal effects.

Temperature drift in your drone’s altitude reading is hardly noticeable when flying high, and may only be a minor nuisance when flying low. But, where it can cause trouble is when using a programmed mode that instructs the drone to fly at a certain altitude. If that happens to be 10 feet or so, then the program will try to drive the drone at that altitude, but in reality is flying it toward the ground. Even at higher altitudes, you can lose your margin when programmed flight decreases your drone’s actual altitude above objects such as buildings and trees.

What to do When Altitude Accuracy is Important

I recently had a client that required drone photography at several specific altitudes above ground level. This job had to do with precision surveying in advance of a construction project. Since my drone’s altimeter would not meet their requirements, they set up a surveying instrument to measure the drone’s altitude (see picture). You may also consider other workarounds, such as:

  1. At the time of your critical photos/videos, record the drone’s altitude, then land and record altitude again. Take the difference for true altitude.
  2. Allow the drone to warm up for several minutes before lift-off. At the end of flight, use the reported landing altitude to estimate in-flight altitudes. (e.g. interpolate the number of feet per minute of drift.)
  3. Use an independent measurement device, such as a laser rangefinder.

Flying Your Drone in Native American Reservation Airspace

Flying in Native American Airspace

Flying in Native American Airspace

A question was raised during my recent vacation to a National Park in Montana: Do Native American Nations have sovereign authority over their airspace? I had intended to fly the Park’s edge region from Tribal lands (which legally complies with the NPS Policy Memorandum 14-05). However, I realized the rules that apply to airspace over tribal lands might be different.

Airspace Sovereignty from the Native American Perspective

A retired chief of police of an Indian reservation (Gila River Indian Community, AZ) advised that tribal governments are very sensitive of their sovereignty and sacred grounds. He recommended that drone pilots contact the tribal government or police department and ask for permission to fly. The tribes appreciate a show of respect by asking. To sweeten the deal, perhaps you as a drone pilot could offer photos and videos that the tribe could use for its own purposes.

Unfortunately, there have been many cases of trespassers desecrating tribal lands and taking sacred artifacts. As a result, tribal governments now employ their own law enforcement officers that patrol their territory on 4×4’s. My understanding is that you do not want to be on the wrong side of a tribal LEO if you meet up with one!

Has Tribal Sovereignty over Airspace been Settled by the Federal Courts?

In my blog “Does an Aerial Drone Pilot have the Right to Fly Over Private Property?” we looked at property owners’ rights to the airspace within their property lines. It would be consistent, then, that Tribal Nations would have the same airspace rights. That is, they own the airspace up to 500 feet above ground level. This policy was affirmed in a 2016 paper by the University of Oklahoma College of Law Digital Commons “Why Indian Tribes Possess the Sovereign Authority to Regulate Tribal Airspace.” However, in this paper, an argument was made that Tribal Nations own ALL of the airspace within their boundaries.

Of course, such an assertion by tribal governments conflicts with federal regulations and FAA jurisdiction. However, the author makes a good point that Native American Nations enjoy significant sovereignty in other areas of the law. Since the airspace jurisdiction question had not been resolved as of 2016, drone pilots should contact tribal authorities and request their permission to fly.

No Fly Zones – Flying Your Drone in Restricted Airspace, Update

FAA Drone Zone

Unlocking an FAA No Fly Zone

For several years, the more expensive aerial drones on the market have been designed with built-in firmware that prevents start-up of the motors if the drone is in an FAA restricted airspace, also known as a no-fly zone (NFZ). These zones are typically found around airports, heliports, prisons, military installations, etc.

Here’s the latest information on No Fly Zones, updating my blogs (Part 1 and Part 2) posted last year.

Identification of No Fly Zones

The easiest way to determine if your intended flying area is in a No Fly Zone, is to check with one of the drone manufacturers’ web sites. For example, DJI posts their NFZ map online at this link. If you haven’t checked the map and you find your drone acting odd, you might be in a NFZ. Odd behavior means it won’t start up or it won’t fly past an invisible barrier.

FAA Permission

If you know your intended flying area is in an NFZ and you need access for a valid reason, there’s a way to get permission. You start with the FAA, which has a new web site portal called the Drone Zone that allows you to ask for airspace authorization.

Enter the information and the FAA will turn around their response in just a few days. Be prepared to offer a good reason for your request. If you’re Part 107 certified, your drone is registered, and you have a valid tasking from a client, then your approval will likely be straightforward.

The FAA will contact the appropriate authority, such as the airport’s Fixed Base Operator, who may come back with restrictions such as flight times, flight days, max altitude, etc. Or, you may be declined. If all goes well, the FAA will issue you a signed form (PDF) authorizing your flight plan.

Drone Manufacturer Unlocking

Submit that form to your drone manufacturer. For example, if your drone was manufactured by DJI, then go to their “Unlock a Zone” portal at this link. Enter the information and the manufacturer will turn around their response in just a few days.

In my experience, the process has been quite fast, with same-day approval from both the FAA and DJI. Once the drone manufacturer has approved your request, they will provide a method to download a firmware patch to your drone. Activate the patch using your drone’s control software. Your permission will typically include a geoposition and date range.

Your Rights to Retrieve a Drone If It Lands On Private Property, Part 2

What If An Irate Property Owner Has Your Drone?

What If An Irate Property Owner Has Your Drone?

Aerial drones are usually reliable, and in the hands of an experienced operator are brought home with sufficient battery power in reserve. However, there may be circumstances when the aircraft can’t be brought home and it lands on someone else’s property. I established in Part 1 that the property owner does not have a lawful claim on your aircraft. In this blog, we review your recovery options in less-than-friendly circumstances.

What Are My Options?

If the property owner refuses to return your aircraft, or allow you to retrieve it, then you should call local law enforcement to intervene. As long as no harm was done, then it’s likely that the property owner will hand over your drone to a law enforcement officer. Although the owner may be reluctant, they may come around after being advised that they face a charge of larceny if they hold onto it. There are several other ways this scenario can play out (such as intentionally destroying your aircraft), but if none turn out favorable to you, then you’ll have to ask for a law enforcement report and proceed with a civil or criminal complaint.

I recently heard of a scenario where a novice was using their drone for low-level spying, which violates state and federal privacy laws. If the property owner gets your drone under these circumstances (using any available means) your claim is going to be an uphill battle.

If your aircraft gets stuck in the owner’s tree or is on their rooftop, then be prepared to pay for a service to come out to retrieve it for you. For example, this may cost you $150 for a tree service to come out, climb the tree, retrieve your drone, and assure the owner that no harm was done to their tree.

Sometimes the best grease is money. If the property owner is annoyed, then you may offer a modest sum for their troubles. Conversely, if the property owner demands a “salvage” fee, then this may be the path of least resistance that gets your aircraft back. Even if the law of ownership is on your side, getting a legal judgment will be costly and take time. In the meantime, you’ll probably have to buy another drone.

There is the unpleasant scenario where your drone damaged property or injured a person (or animal). In such a case, your drone deprived the owner of their full enjoyment of the land and your situation has become a whole lot more complicated. This is why you need a good liability insurance policy.

What if the Property Owner Refuses to Return My Aircraft?

Aerial drones can be expensive, with the value of some in the thousands of dollars. At this price point, a court proceeding may be worth the cost. For less expensive drones, a court proceeding may give you some degree of satisfaction but the cost may exceed the drone’s value. Some property owners are so belligerent that they will destroy your drone. I wish I could be gentler in advising that you may need to be prepared to accept the loss of your drone.

In Any Scenario with Complications, Document Everything and Take Pictures

If your operations require flying over private property, then carry an insurance policy that covers liability AND loss of aircraft. If it goes down, then collect as much information as possible about the circumstances, take pictures, print out your controller’s log files, and take names. When dealing with property owners, always be professional and affirm their rights as well as your own. Even though the law is on your side, the property owner has possession of your drone so carefully assert your rights in the kindest manner possible.