There is such a thing as
too much data
Less data, more accurate deliverables
Human resources, software, and time all cost money, and processing more data takes more of all three. In a research setting with an unlimited budget and no project deadlines, collecting more data is an option. However, if you want your drone program to take up less time and cost less money, then the objective is to use as little data as possible to get the results you need.
The surveyors that we work with are not running a research project; they are running a business and need the drone to save them time and money so that they can be more profitable. So the goal is to get about 0.1' vertical accuracy in the fastest most efficient way possible.
The drone benefit of field time savings is real and comes from the ability to substitute a quick drone flight for the time-intensive process of walking a grid over an entire site. However, there are a number of common misconceptions about data collection and processing that lead surveyors to collect too much data. This may sound counter-intuitive, but at Aerotas we have processed tens of thousands of projects and can say with confidence that more data is not always better when it comes to drone data processing. The take away is that you can spend less time in the field, spend less time processing the data, and get a more accurate deliverable by collecting fewer images.
Common Misconceptions
More photos can make up for other mistakes.
False. If there are mistakes in mission planning, for example flying too low or setting too few ground control points, more photos will NOT solve any of the problems.
I don’t want to have to refly a site, so I’ll just fly it twice just in case.
False. If you fly a site twice, often there are mistakes that aren’t fixed by a second flight. For example, improper flight altitude, poor mission planning area, and bad GCP placement are all not solved by extra flights. Even flying a site 10 times won’t make up for mission planning errors like this.
Someone else (like Aerotas) is doing my data processing, so it doesn’t hurt me if I take too many photos.
False. Processing time increases, and file sizes increase. Everything takes longer: field data collection, data processing, uploading and downloading files, importing files into other software. This often leads to additional dollar costs for processing as well.
At the very least, taking more photos doesn’t hurt, right?
False. Collecting too much data often leads to WORSE overall accuracy. Flying too low in partly vegetated areas, or too low with not enough GCPs, or with too high overlap can all cause for WORSE accuracy, in addition to taking more time to collect and process.
I need to fly low because I need THE BEST accuracy on this project.
False. There is no such thing as “the best” accuracy on a site because there are always trade-offs. Using laboratory-grade laser measurement tools can get accuracy down to 0.00001’, but of course would take years to survey a whole site. Likewise, total stations can make more accurate measurements than any drone photogrammetry tool but are nowhere near as efficient. And a tool like Google Earth is faster than a drone, but nowhere near as accurate. Drones are most effective in the 0.1’ to 0.5’ RMSE accuracy range. But every job should start with knowing what the required accuracy is. If your answer is simply “the best,” then be prepared to spend a lot of time on that project.
Less data, more accurate deliverables
Saving time in the field and office is a very nice benefit. But, at Aerotas we understand that accuracy is paramount to each and every project, no matter the scope. This article is not an attempt to cut corners, rather its aim is to offer tactical solutions that will save time and deliver more accurate results.
There are two key factors to consider: FIELD TIME & PROCESSING TIME
Field Time
reasons why you are spending too much time in the field
Overlap overkill
Flying too low
Crosshatch patterns
Adding oblique photos
Adding manual flight photos
Flying extra missions “just in case”
Setting too many GCPs because you are flying too low
These missteps burn time in the field and can 4x your processing time in the office while adding no value to the end product.
Solutions
Fly higher, ~250’ AGL is the Goldilocks Zone
Use a lawnmower (boustrophedonic) flight path, not crosshatch
Collect nadir images only, no obliques
Only collect photos using the autopilot
Plan the mission right the first time, and avoid extra flights
Fly higher and set fewer control points
Processing Time
Proper mission planning certainly helps to manage processing time. Adding more data means that a project will take more time in the field, take more time to process, use more data on computers and tax networks, and will be more challenging to manage in the various software programs utilized in the data processing workflow.
Processing time scales nonlinearly
2x Photos = 4x Processing Time
In this example, ~800 images were collected. Proper mission planning would have resulted in ~200 images. 3 out of 4 images had to be discarded in order to deliver an accurate model.
Impact
Numerous erroneous matches
Troubleshooting took days, not hours
Took 16x as long to process
This project was delivered late
Problems with too much data
More time in the field
Longer processing times
Larger / more cumbersome files
Erroneous matches
Collecting too much data decreases the accuracy of the finished deliverable because of erroneous matches and the introduction of too much noise in the model.
Erroneous Match
Erroneous Match
Solutions
Fly higher
Lawnmower, not crosshatch
No overlap overkill
Plan the mission right the first time, and avoid extra flights
Mission planning is the answer. Flight Ops can help.
When you use Aerotas to process your drone data, you immediately get access to our Flight Ops team. The sole responsibility of Flight Ops is to guide your mission planning and data collection process. This will ensure that you are successfully planning missions, setting UAS-specific ground control, and getting the most accurate results possible from your drone-collected data.
Our Flight Ops team is comprised of pilots who have overseen thousands of projects. Aerotas always makes accuracy recommendations after the data has been processed. But, now you can get advice before you fly. Getting a second opinion on a mission can increase the likelihood of collecting good data with fewer fieldwork man-hours. Getting it right the first time also helps you avoid re-visits.
FLIGHTOPS@AEROTAS.COM | (949) 386-2277