How to Map Large Areas
Tags: Surveying, Mapping, How To, Drones

How to Map Large Areas

A Workflow for the Commercial Drone Industry

By Eric Harkins, Founder and CEO, Back Forty Aerial Solutions

If I learned anything from my days working in the restaurant scene, it is this: you have to take time to save time. The commercial drone business is no different, especially when it comes to mapping large areas. Large plots pose a unique set of challenges including maintaining line of sight, optimizing battery life, collecting and organizing large amounts of data, and ensuring safety across such a large area. Because of the sheer amount of data involved, extra care must also be taken to produce a cohesive, high-quality map without blurred images or gaps in coverage. Technical blunders cause unnecessary delays, and the failure to produce a successful map may even result in the need to re-fly a mission altogether, costing drone operators valuable time and money

However, by taking the extra time to plan properly, equip properly and not rush through the execution, most major issues can be avoided. Additionally, settings expectations with customers beforehand is a wise idea. To this end, we at Back Forty Aerial Solutions developed the following workflow for mapping large areas. It is focused on using DJI equipment, but many of the tips are still applicable to other platforms and planning for efficiency.

This workflow was developed from using a 450 acre area of interest (AOI) we flew in mid-September 2016. You’ll see in this example that there are rolling clouds- we discussed current weather conditions with the landowner prior to flying and showed some examples of what the output could look like, he was fine with it. After some trial and error, we’ve concluded that a Phantom 3 Advanced, paired with the DroneDeploy app, is a cost effective system to use for orthographic mapping.

Pre-Site Planning

Review Satellite & Sectional Maps to Identify Barriers

The last thing an operator wants is to be surprised by a tree line or other unexpected obstruction. This not only creates a potentially unsafe situation, but it also cuts away from precious flight time as an operator scrambles to adjust to an unforeseen obstacle. Because maintaining line of sight (LOS) is so critical, I suggest starting your planning process by pulling up a satellite map, such as Google or Bing, to take a close look at the area you will be flying. Scan the maps for potential barriers to LOS. Check your local VFR Sectional charts for towers and the like. Take this opportunity to get a good sense of the roads and landscape and start thinking about places to set up, take off, land for battery swaps and post up for flight observations.

Scouting ahead should allow you to create a rough estimate of the time you’ll be spending on site. The DroneDeploy mission planner gives a good estimate of flight time for a large area. However, I recommend conservatively tacking on 20% to that time estimate to allow for flying to and from your start/end points, as well as for time spent on battery swaps.

Choose the Right Flight Parameters to Ensure Data Quality

Reviewing flight plan with customer prior to take-off

DroneDeploy’s software makes flight planning and flying with DJI products pretty simple. However, it’s more of an art than a science, and while the DroneDeploy interface makes it easy to plan flights, it is still our responsibility as operators to get the data we need. Follow these simple guidelines to help ensure data quality and maximum battery life.

Maintain Simple Boundaries- Don’t get carried away drawing complicated polygons for your boundaries. Doing so can leave you prone to tight corners and areas of questionable coverage. Instead, maintain fairly simple shapes that allow for smooth, consistent coverage. You can simply crop out unneeded areas when you upload to DroneDeploy.

Overshoot Your Perimeter- Our experience has shown that areas on the outside transects are more susceptible to artifacting/ distortion when processed through DroneDeploy. Because of this, we overshoot our perimeter by 10–15%, aiming for one transect outside of our AOI boundaries. This may sound like a lot, but the extra time it takes to fly the expanded perimeter is significantly less than the time it would take to re-fly an entire mission if the original data was distorted.

Area of interest (outlined in red) showing extra flight plan coverage, visual observation points and planned battery swap location

Decide on Altitude Parameters- Flying at higher altitudes allows for better coverage per battery, which can be especially important when covering large areas. However, the higher the altitude, the lower the ground resolution. Because of this, it is important to agree upon survey parameters and set expectations for ground resolution with your client prior to flying, and balance this out with your battery needs.

Set a Minimum 70/70 Overlap- Maintaining a minimum 70/70 side/front overlap will give processing software a better chance of tying together points between images. I’ve even talked to operators who do as much as a 90/90 overlap. If you are flying for 3d point cloud generation, this 90/90 overlap is where you will be living.

Fly Lengthwise- Whenever possible, orient your flight lines lengthwise, i.e. — parallel to the longest edge of your AOI. This allows for clear edges without wasting time by turning more corners. That being said, if you are flying in moderately windy conditions, do consider the direction of the wind. As a general rule, you should avoid flying across the wind, since it increases the likelihood that the drone’s legs will angle into the camera’s field of view.

This allows for clear edges without wasting time by turning more corners.

Turn Off Automatic Camera Settings — If you are fairly familiar with the DJI camera settings, you may be able to improve image quality and create more consistent exposure by turning off the automatic settings and instead manually setting them in the DJI Go app. However, this may backfire on days with rolling cloud cover, so it is important to be aware of the conditions and choose wisely.

Divide Area into Multiple Missions

Some operators prefer to draw one large mission in DroneDeploy. Although this is a useful way to get an overall estimate of flight time, we prefer to create multiple flight missions that divide the AOI down into manageable chunks. This allows us to more easily maintain LOS, plan battery swaps and maintain simple boundaries and limit the amount of tight corners.

Maintaining LOS and planning battery swaps can be difficult when flying one large mission

Breaking a large mission into smaller chunks allows for shorter transects and easier logistics planning

If you divide your AOI into multiple maps, it is important to keep them organized with consistent naming conventions. We generally start at the NW corner of an AOI and call that N1 Property Name, then move east with N2 Property Name and so on. Picking an arbitrary north/south dividing line, such as a road, can further divide your labels.

Note: Images from multiple flight plans can be uploaded to one map for processing as long as the total images do not exceed the per-map upload cap on your DroneDeploy plan. However, flight logs will only be available for the flight plan to which the images were uploaded.

Packing

Forgotten or unprepared equipment can waste lots of time or, depending on how far you’ve traveled, may even cause the day to be postponed entirely. Maintain a master packing list to be used for all large missions. For each new mission, consult the master list and add or delete items as needed. The night before, make sure you’ve packed, double checked your list and charged all batteries and equipment.

Sample Packing List (based on 450 acre flight):

DJI Phantom 3 Advanced x2 (because “two is one, and one is none”)

64gb Micro SD card x2

Micro SD to USB reader x2 (one in each case and an extra in each vehicle)

Phantom 3 battery x5

Fully charged laptop & charger (for reviewing captured images in the field)

400w inverter (hardwired to the truck battery, we plan on upgrading to 1000w)

DJI Phantom battery charger

3 battery, parallel charger

LiPo guard battery bag x2 (to safely charge batteries within)

2 gallon cooler (to cool batteries after each flight and get them onto the charger faster)

Stay-dry Ice pack x2 (goes into cooler and doesn’t sweat)

ND lens filters (to prevent whitewash on sunny days)

In-Field Operations

Maintain Safety

Safety is paramount, not just for you and your team, but for all of us. When a drone operator makes the evening news for being an unsafe pilot, our reputation as an industry suffers. Wearing bright colors in remote areas, adequately marking your takeoff and landing zones and maintaining LOS at all times can go a long way toward promoting safe flights. Don’t fly in unsafe weather conditions — it’s not worth the risk. Service equipment and routinely inspect it before and after each flight to prevent dangerous malfunctions. Additionally, make sure to keep in constant communication with your team through cell phone, radio or a device like Beartooth.

“When a drone operator makes the news for being unsafe, our reputation as an industry suffers,” says Eric. [click to tweet]

Bringing a spotter along both helps with safety and also makes missions twice as manageable. A second team member is useful for running interference on any curious passerby that can distract your pilot in command, as well as provide an extra set of eyes to scan the sky for unforeseen obstructions. In addition to helping with these safety measures, the team member can do double duty by moving batteries into and out of the cooler and field checking photos, further improving your speed and efficiency.

Optimize Battery Life

Unless your battery collection looks like the picture below, you will need to have a plan for charging and rotating batteries. Taking a few steps to optimize battery life for each mission can save a considerable amount of time in the field.

#dronegoals

Set up a safe home point, then drive as close as possible to your starting point and launch. Plan your battery swap locations ahead of time and drive to them as your mission progresses. The FAA has stated that this is acceptable in sparsely populated areas. I do however want to address the difference between using an iOS device vs an Android device. Android will NOT allow you to run multiple, simultaneous connections to a DJI drone. Therefore, in flight, you cannot change the home point between the take off point and the controller’s location on an Android device.

Another trick to optimize battery life is, in the DJI Go App, change the RTH battery threshold to lower than 30%. Alternatively, you can set your controller as the home point. When your battery starts to get down to 30–40%, stick close and you may be able to squeeze out an extra transect or two, depending on their length. Do make sure you know your limitations though, and always maintain enough battery life to land safely. You are always responsible for your aircraft.

A savvy pilot should always be keeping an eye on remaining battery life. If you know you have 33% life remaining but are about to start a 1500 foot transect that ends away from your intended landing zone you should be planning accordingly. Go ahead and take control at the end of the transect closest to you and land. In other scenarios, when you receive the low battery signal attempt finishing the transect ending closest to you, then switch back into P-mode and manually land. Alternately, if you set controller as the home point you can just hit the home button in the app or on the controller. The mission will resume at the front of the next transect, avoiding the need to re-fly a transect that was interrupted midway through.

During battery swaps, immediately toss the used battery into your cooler with the dry-packs. Set a timer and pay attention to it when it goes off. Think of a NASCAR pit crew — in and out. To avoid confusion, make sure to label batteries, either with a vinyl sticker or a sharpie.

Check Data in Field

Despite the best preparations, data quality issues do still occur. Cameras malfunction and fail to take pictures, GPS doesn’t geotag images correctly or photos end up overexposed. These issues are sometimes out of your control, but two days after you’ve left the job site isn’t the time you want to discover them. To check data in the field, bring multiple micro SD cards to a site and swap them out after each section has been flown. While the operator is flying the next section, another team member can move the images from the previous mission off the SD card and onto the laptop, then format the empty SD card for the next flight. I suggest taking a moment to separate the images taken during RTH/landing from your AOI images. Uploading these by accident can cause issues with processing your imagery.

The really important step here is to get on WIFI or if a cell signal is available, pop up a WIFI hotspot and do a mock upload to the DroneDeploy website. Drive back toward civilization if you have to. You can quickly check for coverage without actually uploading your images. Just hit that “Upload” button and select your images to get to the screen below.

‘Take time to save time’ in action! We now know we need to re-fly a portion of the mission.

Develop Your Own Routine

Successfully mapping a large area can be a daunting task. There is no shortage of challenges that threaten to cause costly delays. Let this workflow serve as a roadmap for your own mapping routine. Take notes along the way, find out what works for you and ultimately refine a plan that suits your business. The extra time you put into these preparations now will be returned to you twofold in the form of efficient, cost-effective mapping missions.

If you’ve read this far you’re probably thinking to yourself, “well Eric, where’s the finished product?” Don’t worry, I didn’t forget!

Behold — the fruits of our labor. Now get out there and fly safe, fly smart, and of course… have some fun!