If you’re considering starting a drone program on your site and you’re new to drone surveying, you’re probably wondering what a drone surveying workflow would look like. How will it change your existing workflows? What can you expect when you go out to fly?
There are a few things to consider here, the first of which is that everyone’s exact drone surveying workflow will look a little different simply because no two worksites are the same. We thought it would be useful, however, to understand some of basics—like what it looks like to actually fly a drone on your site; how ground control setup plays into everything; and how different things affect the quality of your data.
Capturing the best data
The biggest issue is how to capture the highest quality data. Truthfully, getting the best data starts when you’re out on the field. Even small mistakes during your drone flight can have big effects on your final survey, no matter what software you’re using.
The main elements that affect data quality are:
- Physical flight (including hardware, height, and speed)
- Image quality, overlap, camera settings
- Ground control setup and sufficient ground sample distance
Actually flying your drone on site
When it comes to actually walking out on site to launch your drone, the flight itself is mostly automated. Apps like GS Pro take all the complexity out of the actual flying—and it’s free. It takes only a couple of minutes to set up your drone’s flight path on a touchscreen, then simply hit Go. There’s no manual control involved.
We recommend automated flying because steady, consistent flight is crucial to image quality. If you have poor quality images, you’ll get poor quality surveys. It’s as simple as that.
We’ll go over the technical side of imagery quality further down, but simple things like reducing blur can be solved with apps like GS Pro.
The importance of ground control
Ground control is vital to survey accuracy. Technologies like on-board RTK will provide improved accuracy in the air, but that doesn’t automatically translate to the same accuracy on ground level. Terrain models corrected with on-board RTK alone are still more susceptible to turbulence, vibration, and camera calibration errors than models generated using ground control points (GCPs).
Without GCPs, combined errors of ten-plus degrees in a drone’s pitch or roll can introduce errors of tens of centimeters in the final survey. Basically, absolute accuracy can be reined in from meters to centimeters with GCPs.
Example planar shift between datasets generated with AeroPoints and those using only uncorrected on-board geotags.
Setting up ground control points traditionally—i.e. with a base a rover—can be slow, costly, and complicated. But establishing ground control with AeroPoints is simple and straightforward. These smart GCPs have a rugged exterior and inbuilt GPS, and are capable of capturing incredibly accurate positional data.
Just like when you’re doing a site calibration, laying out ground control needs to be thorough and takes planning. GCPs must be evenly spaced all around the edge and optimally placed throughout the interior of your site, else risk warping in your final survey model.
(But if you’re using a different kind of workflow, like Propeller PPK, the need for traditional ground control is significantly reduced. Read more about that solution at propelleraero.com/ppk)
Keep in mind possible line-of-sight obstructions when planning placement. Set down all of your GCPs in clear view of the sky. Avoid putting them under trees, near fences, or any other obstacles.
Photogrammetry, image overlap, and camera settings
When it comes to the images themselves, there are a few technical specifications they must meet in order to be stitched together to create a survey.
Drone imagery is the foundation for a survey. These photos and their corresponding positional information are stitched together using the science of photogrammetry.
At its most basic, “photogrammetry” is measuring via photos. It might sound dry and complicated, but its inner workings define the way we fly.
When you send your drone up, it takes pictures of your site with lots of overlap. About 80% in the necessary overlap for each picture, and your aspect ratio should be set to 3:2 on your camera. This for two reasons:
- For the computer to stitch images together to make the orthophoto.
- To capture enough angles of each feature to model it in 3D.
Essentially, if you see the same feature from three or more known positions, you can triangulate its location in space, getting those exact X, Y, and Z coordinates. A feature is any visually distinct point in an image.
If you took an average image from your survey, you’d easily be able to pick out many “features” between different photos. The more features you match, the better you can relate images to one another and reconstruct objects pictured in them. This is exactly what photogrammetry software does for one feature, and the next, and the next, and so on, until it’s covered your entire site.
With a lot of these features—think millions—you can create a “cloud” of points. Each point has a matched feature describing your surveyed area in that location. You can then turn your point cloud into any regular outputs used in geospatial software, like a 3D mesh or digital elevation model (DEM).
Your average drone surveying workflow
Now that you have the basics of what goes into a drone survey, let’s outline an average, boots-on-the-ground workflow of what it looks like when you capture your data with a drone and AeroPoints.
- Map out your driving route and ground control placement
- Safety assessments and traffic management
- Ground control placement
- Drive your site and layout AeroPoints, turn each on as you go
- Launching your drone
- Set your route with an mission-planning app, and save mission
- Remove your drone from its case, attach the propellers, insert a full battery, place in open space for launch
- Launch drone and monitor flight through handheld remote
- Landing and wrap up
- After your drone automatically returns home, place it back in its case
- Drive and pick up your AeroPoints in reverse order to ensure they’ve had enough data-capture time. Pressing the button before picking them up off the ground
- After the button has been pressed again, they’ll look for a WiFi signal to automatically upload data
- Return to the office, upload your imagery to a cloud-based processing platform like Propeller.