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 Accuracies – Comparing Accuracies
Clearly the most important thing in land surveying,
in my opinion anyway, is ACCURACY! I believe this to be one of the main reasons
surveyors are hesitant to add this tool to the toolbox. There are 2 different accuracies to take into
account when capturing data: absolute accuracy and relative accuracy.
Factors that contribute to accuracy issues:
•
Flight Altitude
– (Careful! – Low Flight could lead to GCP issues)
•
Overlap – 75
frontlap x 75 sidelap is ideal, but could be brought down to 70x65 if needed.
•
Lighting -
(Poor or Inconstant – Shadows/Bright Lights)
•
Type of Terrain
- Vegetation v. Hardscape
•
Geography /
Topography - (Steep (without proper GCP / Flight Planning)
•
Quantity of Ground
Control (Proper Distribution of GCP)
• Camera Quality – In my opinion, although
important, this is the least important of all factors. If other sources of error are present, then a
better camera will NOT improve accuracy at all. A 20mp camera with proper
workflow should yield extremely accurate data.
What is GSD? You will hear, or have heard, the term GSD when it
comes to drone flights. This is
something you will want to be aware of when fully understanding accuracies. The Ground Sample Distance is the distance
between center points of each sample taken of the ground. So basically, the GSD
is how big each pixel is on the ground. The GSD is determined by the geometry
of the camera and its altitude above the ground.
Here are a
couple of calculators I like to use when calculating GSD.
·
https://www.propelleraero.com/gsd-calculator/
·
https://support.pix4d.com/hc/en-us/articles/202560249-TOOLS-GSD-calculator
Below is a screen shot comparing accuracies via total station, RTK GPS and Photogrammetry.
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