Our Consulting & Services Manager, Shawn Herring, wrote a great article on surveying industry insights on drones. Here's a portion of the article:
Drones, drones, drones! Over the past few years this may be the biggest industry trend for land surveyors and civil engineers, and probably just as important of a shift as GPS data collectors.
I started a surveying firm in 2010 with a focus on ALTA surveys, general boundary and topo projects, mass volume calculations, as well as construction staking. We then got into a little LiDar scanning and really jumped into aerial data capture about 5 years ago and have never looked back!
I love data capture, whether from the ground or from the air, and trying to keep up with the daily technology trends and advances can sometimes be overwhelming. I thought I’d put together this article on some of the lessons we’ve learned over the past few years when it comes to utilizing a drone in our survey department.
The Field Prep
No, you can’t just show up to a site, drone a drone, and expect to take a nap while the drone magically does your job for you… yet!
There are many things to do prior to flying a drone. Gain FAA approval if needed, set ground control points (GCP), “prepare” the site by calling in Blue Stakes (811, Julie, etc), paint some stuff, plan which flight pattern you’ll use, etc, etc, etc. And each site has it’s own challenges that need to be addressed. There is no “one flight fits all” scenarios for most firms. A bit more explanation on these is below:
· FAA Approval – Aside from the requirement of becoming Part 107 Certified for commercial pilots, some projects may require FAA approval to fly within controlled airspace. Plan ahead, as some locations may take time, and some locations may be immediate.
· Ground Control Points (GCP) - Ground control is essential in ensuring accuracy of your flight linework/DTM deliverables. GCPs are marked points on the ground that have a known geographic location. GCPs coordinates are used by drone mapping software to accurately position the collected data in relation to the real world. Think of a flight at 400’ compared to a flight at 200’ with identical GCP quantity. GCPs can be as simple as using a can of paint (typically for hard surfaces) or using one of many methods of target creation.
Not all GCP targets are created equal! I prefer a brightly colored 24”x24” target that can easily be identified for manually GCP tagging, or even automatic tagging in some softwares.
GCP placement is very important. Flight altitude is key to proper planning of GCP placement. Low altitude flights typically result in the need for additional GCP’s.
· Paint some stuff! We try to call in blue stakes to paint underground utilities such as gas, telecom, fiber optics, etc. And in developed areas, I typically send my survey crew out to mark things such as manhole depths, flow direction, etc. Having all this data in your images can really save unnecessary trips out to the site and answer questions immediately as to not slow down the design process.
· Flight Patterns – There are several flight options in most drone mapping software’s, but 2 patterns remain consistent across all platforms.
o Area Survey (NADIR) – This pattern typically consists of no oblique images.
o Crosshatch – For Example, this flight pattern goes East-West, then flies the same area North-South. This pattern typically has a 35-degree gimbal angle for oblique images.
So which flight pattern is right for you? 95% of the 500+ flights I’ve done the past few years have been done using the area survey option. I’ve tested over and over the need for a cross hatch pattern, but for most project the data value just isn’t there. You would think that more coverage is better right? Instead, the cross hatch causes an increase in field time, an increase in data processing time, an no real major measurable benefit in accuracy. However, crosshatch survey is at times needed. For areas with highly repetitive land, like crops and dense vegetation and verticality concerns, a cross hatched pattern may be useful. We do a lot of ALTA surveys of apartment complexes, and with all the buildings and vegetation, we sometimes use the cross-hatch pattern.
If you’d like to see some data from each type of flight pattern, feel free to email me and I will send one of the projects where we’ve used both options for comparison purposes.
The following two images show the above mentioned flight types, and the flight data difference between the two.