The document discusses drone surveys and applications in civil engineering. It provides an overview of how drone surveys can be used for mapping, surveying, construction monitoring, inspections, and other applications. Drones allow data to be collected from the sky efficiently and safely. High-resolution orthomosaic maps and 3D models can be created through drone photography and post-processing software. This provides accurate spatial data that saves time and costs compared to traditional surveying methods.

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INDEX
Sr. No. Topic Page No.
01. Title 02.
02. Introduction 02.
03. Background: Explosive Market Growth 03.
04. An Overview Of Commercial Drone
Application
04.
05. Mapping And Surveying Applications 08.
06. Add In 3D 13.
07. Post Processing 14.
08. Reference 15.

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Title
Drone Survey
Introduction
Drone surveys are a faster, safer and more cost-efficient way to survey at height. Sometimes
referred to as aerial surveys, UAS (Unmanned Aerial System) surveys,
or UAV (Unmanned Aerial Vehicle) surveys, drone surveys are an increasingly popular method
of surveying form the air.
An unmanned aerial vehicle (UAV), commonly known as a drone, as an unmanned aircraft
system (UAS), or by several other names, is an aircraft without a human pilot aboard. The flight
of UAVs may operate with various degrees of autonomy; either under remote control by a
human operator, or fly autonomously based on pre-programmed flight plans.

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Background: Explosive Market Growth
The drone industry is big news these days – hardly a day goes by without some drone-related
item in the news, and one drone industry forecast after another seems to hype the seemingly
unlimited potential for the drone market.
The market is growing faster than even the analysts can predict: a review of market reports
released over the past few years makes it abundantly clear that the explosive growth of the
civilian drone market took most analysts totally by surprise, and leaves the future of the market
anyone’s guess.
In addition, dollar value estimates of “the drone market” vary widely, and much depends upon
what analysts choose to measure. There is of course, the potential value and sales of the drones
themselves; but there has also been considerable speculation on the value of commercial drone
applications.
There have been significant advances in drone technology in the last 12 to 18 months. Prices
have also come down, scale has increased, and the latest UAV (Unmanned Aerial Vehicle)
predictions for 2020 in a 2016 Aerospace Forecast published by the US FAA estimates the
number of drones likely to be in civilian hands by 2020 at a whopping 542,500 units. A recent
drone industry report by Business Insider estimates Enterprise Drone Shipments alone will top
US$12 billion by 2021, stating that while technological barriers may still limit adoption in some
areas, they still see the pace of adoption increasing.

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An Overview of Commercial Drone Applications
While the consumer market for drones may be topping out (perhaps the Christmas novelty is
finally wearing off), the market for commercial drone applications continues to expand at an
exponential rate. One of the key areas of expansion is in the area of land mapping, ground and
structural analysis.
One US startup that provides cloud-based post processing of map photographs and imagery,
noted than in the first 12 months their users collectively mapped a million acres, but the next
million acres was achieved in less than four months. This rapid rate of growth not only
underscores the value that of drones for land mapping, but also reflects a larger trend in the
industry.
Film, TV and Video
The film and video industry was one of the first to realise the potential of drones, and the internet
is now awash with spectacular aerial videos shot from drone users all around the world. Almost
every independent camera operator and production house seems to have at least one drone ready
to go, and with a little practise its possible to achieve great shots in very little time. For feature
films and television, drones have increasingly replaced helicopters for aerial footage. Not only
are the cost saving significant, but the possibilities are much wider. Shots that start in a room,
pull back out of a window, up and over a house, up over the street, neighbourhood and entire
town are simply not possible with a conventional manned aircraft.
Stability and precision has come a long way in a very short space of time, so much so that its
now possible to repeat shots, following the exact same flightpath, speed, pan and tilt of the
camera, allowing for rapid application of CGI and effects in post production.

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Surveying and GIS
Surveyors and GIS professionals are using drone mapping to achieve tremendous time and cost
savings on surveying and mapping projects. Time spent collecting accurate data is vastly
reduced. By acquiring raster data from the sky – in the form of geo-referenced digital aerial
images – surveyors can gather millions of data points in one short flight.
Less time spent on the ground also means staff safety is improved by minimising risk to
surveying teams when out measuring locations such as construction sites, unstable slopes or busy
transport routes.
Construction
The applications here are similar to those of surveying, but with the addition of an aerial
monitoring capability. Consequently, this is one of the fastest growing areas for drone adoption.
There’s a lot to keep track of on a job site—project progress, the location of equipment, the
volume of materials left—and the ability to quickly get an aerial view or 3D model makes it all a
lot easier.
Mining
For the mining industry, it is the ability to quickly and cheaply calculate aggregate volumes in
open-cast mine situations that is becoming a game changer.
Agriculture
Farmers are now using drone-generated maps to identify areas of crop variation and damage, to
help diagnose causes of damage (such as irrigation problems and pests) and prescribe solutions,
such as variable rate nitrogen applications.
Most drone imagery captured for agricultural analysis involves NDVI or the Normalised
Difference Vegetation index. This is a graphical indicator that can be used to analyse and assess
whether the target being observed contains healthy vegetation or not. It requires a combination of
standard photographs, taken within the normal visible (RGB) spectrum, and photographs shot in
the near-infra-red spectrum.

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Mapping and Survey Applications
How Can Drones Help?
There’s a lot of work important being done on sites today that could be made more efficient by
the use of drones. Prospective sites ready to be developed need to be surveyed and terrain
mapped. An understanding of the topology and geology are essential for initial planning and
design.
Sites undergoing development and construction need careful management, including ongoing
surveying, monitoring of work in progress, inventory and supply management, and optimisation
of operations.
From a CAD and design perspective, there is reality capture: the ability to overlay digital models
with the actual construction site for tasks like spacial planning and volumetric calculations.
For complete and finished structures, there’s the need for ongoing inspections for regulatory and
safety compliance. Especially for tall, hard-to-reach structures, such as cell phone towers (not
many in Hong Kong), power and phone line pylons, bridges, and skyscrapers (a lot in Hong
Kong!), inspections of this nature are always a challenge.
The way many of these tasks are carried out today can sometimes be a bit of a struggle.
Satellite imagery can be used to as part of the planning and design process, buts it’s often of low
resolution, and not up to date. Many satellite images date quickly, especially urban areas in Hong
Kong, and are not an accurate reflection of what’s on the ground right now.
Aerial images via conventional aircraft can provide higher resolution, and more current. But the
cost of aerial photography in Hong Kong is often prohibitive, and even if it isn’t, access over
most urban areas would not achieve great results. The minimum altitude for manned aircraft is
500 ft above water and the countryside, and 1000 ft over the urban area – often too high to
capture anything in considerable detail.
Ground-based surveying tools can’t always capture all the data required, and sometimes require
portions of a site to be shut down, which of course adds to costs. Generally speaking, multiple
methods often need to be employed to collect all the necessary data – and it can still be
fragmented and incomplete.
Safety is always an issue on any construction site, so reducing the number of people that need to
visit a site, and/or be on site to analyse progress, check inventory, and survey structures is always
going to have a positive effect on safety.
In structural inspection, often the only access is to manually climb or rope-access tall structures
for inspection, or utilise expensive and potentially dangerous helicopter flights.

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The Drone Advantage
1. As mentioned, drones are being used increasingly by surveyors, project managers and
GIS professionals around the world to save time and costs on surveying and mapping
projects. In the field, time spent collecting accurate data is vastly reduced by using
drones.
2. By acquiring raster data from the sky – in the form of geo-referenced, ortho-corrected
digital images, with resolutions down to 1.5 cm / 0.6 in per pixel – millions of data points
can be gathered in one short flight.
3. And this capability can be repeated over time, building an ongoing report and archive of
construction and development in progress.
4. For inspection, the ability to get up close to almost all areas of a tall and generally
inaccessible structure greatly speeds up assessment and analysis, enabling more efficient
decision-making for follow up action.

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How it Works
A set of digital images or photographs taken by the drone at a pre-set, consistent altitude over the
site are digitally processed and stitched together into an orthomosaic. An orthomosaic is
essentially a grid of photos, geometrically-corrected to accurately map the survey site being
covered.
Orthomosaics
Because the drone is continually using GPS to maintain its flight path, position and general
stability against wind and turbulence, the GPS data is also used to geo-tag each photo as its taken
during the mission. These geo-tagged photos can then be reassembled by post processing
software into the orthomosaic within the parameters of a known position on the Earth’s surface.
Accurate orthomosaics require images be taken with a significant degree of overlap, usually at
least a 70 percent overlap between one image and its adjoining images. Images also need to be of
a reasonable resolution (12MP is a good starting point), and taken in reasonable light conditions
(a bright but overcast day is ideal. Strong sunny days may have better colour rendition, but
produce dark shadows that may lack detail).
Greater Accuracy
Most drone-collected geo-tagged images can produce orthomosaics with accuracies and detail
down to 5 cm / 1.9 in per pixel, just based on the GPS data collected by the drone.
For more stringent survey requirements, additional accuracy can be achieved by establishing a
Ground Control Point (GCP) before the flight commences. This GCP could simply be a fixed
object, such as a post or the corner of a building, or a pre-determined latitude / longitude point
set in Google Earth. This GCP can be uploaded into the drone’s flight plan software before the
flight, and is then used a reference point during photo taking and post processing.
Certain advanced survey drones can receive real-time in-flight data corrections during a mission,
streamed from a fixed Virtual Reference Station (VRS) on site to achieve X, Y, and Z accuracy
down to 3 cm / 1.2 in per pixel, without needing Ground Control Points.
Controlled Flight
With their in-built GPS and highly responsive flight control systems, today’s drones are able to
fly and maintain very specific, accurate zig-zag flight patterns, flying backwards and forwards
across a site until the entire area is photographed and mapped with the degree of precision and
overlap needed. They’re able to fly slow enough to capture sharp, clear images without motion
blur, and their powered gimbal systems ensure the camera is maintained at a stable, consistent
nadir angle throughout the flight.

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Pre-Programmed Flight
Because of this need to fly and maintain a very specific, accurate flight pattern, the site map and
flight plan are pre-programmed, saved, and uploaded to the drone before the mission
commences. This can be done either on site, or beforehand in an office, but requires an internet
connection so the flight plan software can bring up a background satellite map of the location to
be surveyed – usually Google Maps or Mapbox.
To set up a mission, the user simply marks out the area to be surveyed on the satellite map,
adjusts the degree of photo overlap required, and the most efficient direction of the flight path
(the optimal flight altitude is usually calculated by the software, but can be adjusted), and saves
the flight plan ready for upload to the drone.
Once the drone is switched on and is deemed flight-ready, the flight plan is uploaded and the
mission executed. The drone takes off, executes the flight plan and takes all photographs entirely
automatically. If a problem or hazard is encountered, the drone operator has manual override via
the flight transmitter / controller, which cancels the flight plan and gives immediate manual
control back to the operator.
Most software solutions are also capable of resuming a flight plan from a cut-off point, should a
manual override be necessary, or should the drone need to return for a battery.

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Add in 3D
If a key requirement of the job is a 3D visualisation or model of the site being mapped, then post-
processing is greatly enhanced if there is a set of oblique images taken around the site from
different angles.
These images are acquired by flying a generally circular path around a site, capturing images at
30, 45 and 70 degree angles, looking inwards from the perimeter of the site. The post processing
software then has a clear set of images of the sides of existing buildings and structures within the
location, which in turn produce more realistic and accurate 3D renderings.
Generally, this oblique angle capture process cannot be executed as part of an automatic flight
plan, and will need to be flown manually by a skilled operator, but the results are well worth the
additional time spent to capture a good oblique image set.

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Post Processing
Once the flight mission is complete and the site fully photographed and mapped, the photographs
and the geo-data need to be processed into an usable orthomosaic map. This can be done with
desktop software solutions, or increasingly, with cloud-based solutions, where the entire photo
set is uploaded to a cloud service, and processed in a few hours, leveraging the power of
distributed processing.
Desktop Solutions
A number of desktop systems are well established, with others appearing more recently.
Principal among these is German-based Pix4D, who offer a range of desktop processing
packages aimed at different sectors, including structure and site surveying, agriculture, and 3D
rendering.
ESRI’s ArcGIS, arguably the world’s most powerful GIS mapping software, is well established,
and has a huge range of applications. ESRI has a new package, Drone2Map, currently in beta,
which enables the creation of orthomosaics, 3D meshes and more inside ArcGIS from drone-
captured still imagery.
Autodesk is offering ReCap 360 as a free download for most Autodesk suites, enabling the
import, view, and conversion of point cloud data. However, you can do very little without
upgrading to the ReCap 360 Pro version, which enables orthomosaic stitching and advanced
editing and measurement tools. The Pro version also offers cloud-based storage.
Agisoft PhotoScan is another stand-alone software product that performs photogrammetric
processing of digital images and is able to generate 3D spatial data.
Bentley, another major player in the infrastructure space, offers ContextCapture which creates
3D models from simple photosets.
Cloud Solutions
Silicon Valley startup, DroneDeploy has rapidly carved itself a major share in the cloudbased
orthomosaic processing arena since launching in 2015. Image sets are uploaded via a desktop
computer, or can be uploaded in the field direct from the capture app (if an internet connection is
available). Processed data sets include orthomosaics, terrain models, 3D models, and crop NVDI
analysis images.
All orthomosaics and models can be viewed online, or downloaded for import and processing in
other desktop software systems. In a similar vein, Maps Made Easy also offers cloud-based map
processing, processing and producing orthomosaics, terrain models, 3D models, and crop NVDI
analysis.

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Reference
www.google.com
www.splung.com
www.civilengineering.com
www.drone.asia
Textbook of Advance Survey