Terrane Aerial Mapping System: White Paper

Executive Summary

Terrane Aerial Mapping employs a SmartPlanesTM lightweight Unmanned Aerial Vehicle (UAV) for

producing low-cost, high resolution aerial photography and digital elevation models (DEM). Applications

include, but are not limited to, construction, exploration and mining, forestry, agriculture, surveying,

search-and-rescue, etc... The UAV output can be used to generate orthophotos with a ground resolution

as low as 4.0 cm. The output DEM’s can also be used for accurate estimates of material stockpile

volumes, cut-and-fill analysis and quarry/mine extraction calculations.

Delivery of a basic orthophoto, raw images and a processing/logistics report are included with every

survey. All data products are reviewed and approved by a professional Engineer or Geoscientist (P.Eng

or P.Geo) before delivery. Most common image and GIS/CAD file-format outputs are available at the

request of the client. Turn-around time for deliverables is generally 1-2 days.

Operationally the UAV can survey an area from 0.1 to 0.64 km2 (100*100 m to 800*800 m) per flight and

fly five to six surveys per day. All UAV flights require Transport Canada approval (SFOC permit) and are

restricted to Class G airspace. Terrane Aerial Mapping will produce and submit all permit applications

on behalf of the client in advance of surveying. Application processing time is typically 14-20 days.

Unlike traditional aerial photography and LIDAR, the cost of surveying with the UAV aerial mapping

system is low enough that actively-changing environments can be flown as frequently as needed,

capturing change-with-time. In addition, the cost of an aerial survey are now within the reach of small

and medium-sized business.

Introduction

Terrane Aerial Mapping employs the SmartPlanesTM UAV (Unmanned Aerial Vehicle) system for low-

cost, high-resolution aerial photography. The UAV output can be used to generate orthophotos with a

ground resolution up to 4.0 cm and high-resolution digital elevation models (DEM’s). Applications

include, but are not limited to, construction, exploration and mining, forestry, agriculture, surveying,

search-and-rescue, etc. The output DEM’s can also be used for accurate estimates of material stockpile

volumes, cut-and-fill analysis and quarry/mine extraction calculations.

The Smartplane system has been in use since 2006 and has been approved for use by over 25 operators

in Sweden, Finland, Germany, UK, The Netherlands, Norway, China, Russia, Australia, Korea, Brazil, and

Moldavia. Terrane Aerial Mapping is the first North American operator of the Smartplane UAV system.

The System

Terrane Aerial Mapping employs a lightweight (1.1 kg) UAV equipped with an on-board digital camera,

GPS and autopilot system (Fig. 1). The UAV is controlled by redundant ground RC radio and a computer

telemetry link. Once launched, the UAV flies a user programed flight block, capturing air photos

approximately every 3 seconds. Photo overlap is user-set in the 75-85% range, allowing for high-quality

photogrammetric image matching. Upon completion of the survey block, the human operator assumes

control and glides the UAV to a landing. The system is designed for safety, simplicity and use in rugged

field environments.

Applications and Deliverables

The system is ideal for collecting high-resolution air photos at the small to medium scale (0.25 to 3 km2).

Common applications include:

Construction/infrastructure base maps and DEM’s

Mining and quarry volume calculations

Material stockpile volumes (e.g. lumber, gravel, rock, tailings)

Mineral exploration base maps

Geology

Agriculture

Forestry

Environment and wildlife monitoring/mapping

Archaeology

Law-enforcement and search-and-rescue

Figure 1 – SmartOne-C Aerial Mapping UAV.

Unlike traditional aerial photography and LIDAR, the cost of surveying with the UAV aerial mapping

system is low enough that actively-changing environments can be flown as frequently as needed,

capturing change-with-time. In addition, the costs of an aerial survey are now within the reach of small

and medium-sized business.

The basic deliverable is a high-resolution, geo-referenced aerial orthophoto of the survey area (Fig. 2).

Surveys are flown at altitudes between 120 m and 250 m altitude, yielding images with ground

resolution of between and 3.9 to 8.1 cm respectively. Additionally, a digital elevation model (DEM) is

constructed and draped with the orthophoto to produce a highly-accurate 3D model of the survey area

(Fig. 3). The images and data can be exported to most common GIS (e.g. GeoTiff) and CAD formats (e.g.

DXF or XYZ). In addition, models and images can be outputted to attractive presentation formats (e.g.

3D - PDF, Google Earth KMZ, JEPG) for client exhibition (Fig. 3B).

Advanced processing options include:

Conversion of features to vector format/digitization

Geological interpretation

Slope and aspect mapping

Line-of-sight analysis

Topographic contouring

Profile generation

Operation

The UAV is powered by a 1500 amp, Li-poly battery which provides energy for 45-50 minutes of flight

time. Other operational parameters are generally constrained by Transport Canada regulation, rather

than the aircrafts limitations. Under a Special Flight Operation Certificate (SFOC), UAV’s may operate

within visual line-of-sight.

An example of a typical flight mission profile is:

Dimensions: 700 m * 700 m (49 ha)

Altitude: 122 m (400’)

Survey Flying Time: 39.3 min (exclusive of take-off and landings)

Flight Lines: 27

Line Spacing: 27.2 m

Overlap: 75%

Ground Resolution: 4.0 cm

Higher altitude surveys (up to 250 m) would increase the effective block-size, but would reduce ground

resolution to 8.1 cm.

Depending on the ease of access and logistics, 4-6 survey missions could be flown on a typical day.

The UAV requires a take-off and landing area of approximately 15 m *15 m, depending on prevailing

winds. Clear cuts, logging roads and lay-down areas are ideal. Low trees do not present a problem, but

high, dense forest or cultural features such as buildings and transmission lines may limit flight

operations. The UAV can overfly water as long an adequate take/off and landing zone is present on

land.

Transport Canada limits UAV flying to VFR (Visual Flight Rules) conditions. Thus thick fog/low cloud or

heavy precipitation would limit flight operations. The UAV can fly in winds of up to 10 m/sec (~35

km/hr.) and in a temperature range of -20 to +40 degrees Celsius.

All UAV flights require Transport Canada approval (SFOC permit) and are restricted to Class G airspace.

Overflying of private property requires land-owner permission. Terrane Aerial Mapping will produce

and submit all permit applications on behalf of the client in advance of surveying. Application

processing time is typically 14-20 days.

Figure 2 – 4.8 cm resolution orthophoto from a single survey flight. Inset demonstrates the level of detail captured by a typical survey when zoomed in.

Figure 3 – Digital Elevation Model application. A) Topographic contours and profiles; B) presentation textured models; C) slope mapping.

Accuracy and Precision

The UAV Aerial mapping system produces an accurately-located and internally precise dataset.

Unprocessed photos are spatially located with an absolute accuracy of the on-board GPS. Typical GPS

accuracy is on the order of 2-6 m, depending on the availability and spatial arrangement of satellites. A

location uncertainty map from a typical survey is shown in Figure 4. However, despite the error

introduced by the GPS location of the unprocessed images, photogrammetric matching produced an

internally consistent image with minimal distortion/errors.

Internal precision is a function of the photo-matching algorithm which is affected by light conditions,

geometry /reflectivity of the terrain and objects within the scene. Edge-distortion is also a factor due to

the lack of photo-overlap at the survey margins. A study by Vallet et al., (2011) compared results of a

DEM produced by LIDAR with a DEM produced by a comparable UAV/photogrammetric system. In this

study, vertical errors in smooth and flat areas were found to be less than 15 cm. In vegetated areas,

error increased within the range of 15 - 80 cm. An empirical example from the Terrane Aerial system is

shown in Figure 5, where the system effectively models details of features 5-10 cm in size.

If higher absolute ground accuracy is required, ground control points can be used. In this method, 6-12

high-visibility ground targets are laid out in the flight block area and their locations surveyed (Fig. 6)

prior to flying the airborne survey. Coordinates of the ground control points are feed into the

photogrammetric algorithm which corrects the orthophoto to the ground-control points. With this

method, accuracy is only limited by the survey type used to locate the ground control points. Absolute

accuracy (without post processing) of 0.75 - 1.5 m is possible using Terrane Aerial Mapping’s Trimble

GEO-XHTM handheld GPS (decimetre accuracy possible with post-processing). Base-station DGPS

surveying of ground control points can yield cm-scale accuracy.

Figure 4 – Input photo location uncertainty map for a typical survey. GPS X-Y location uncertainty is delineated by ellipsoids (maximum of 5.3 m in this example). Vertical uncertainty is illustrated by the ellipse color (maximum of 4.8 m).

Figure 5 – Empirical example of DEM precision. Small barn in orthophoto is 10m*10m in size. Inset detailed DEM of barn shows excellent detail, imaging individual roof rafters, tractor wheel-ruts and a 15 cm deep drainage ditch. Measured horizontal dimensions of the barn in the orthophoto are accurate to within 3.8 cm.

Figure 6 – DGPS surveying of ground control point.

Volume Calculations

High-resolution output DEM’s can be used to estimate the volume of material stockpiles (rock, lumber,

gravel, tailings etc…) or to calculate extraction amounts from quarries and open-pit mines on a regular

basis.

Figure 7 shows an example of a volume calculation for an irregular shaped gravel stockpile,

approximately 68 m*12 m*5 m. The DEM (Fig. 7, inset) can be used to calculate the volume of the pile

above a given datum. Using a base-datum of 44 m, the stockpile contains 1936.4 m3 of gravel and

occupies a 2D surface area of 816.6 m2. Volume and area estimates based on higher base line datum

elevations are shown in Table 1.

Figure 7 – Volume calculation of an irregular gravel stockpile. Base image is an orthophoto generated from a 120m altitude survey. Inset shows cropped DEM used for volume estimates in Table 1.

Table 1 – Volume Estimates for Gravel Stockpile shown in Figure 7.

Datum Elevation Area -2D

Area -3D

Volume

(m) (m2) (m2) (m3)

44 816.6 1009.5 1936.4

45 664.9 832.0 1193.7

46 476.0 599.0 622.3

47 273.1 342.4 250.2

48 107.8 134.0 64.6

Tests conducted by the manufacturer compared stockpile volume estimates produced by the UAV

system, against volume estimates obtained by traditional DGPS ground surveying and LIDAR (Table 2).

Volume estimates were conducted on twelve different stockpiles. All stockpiles were surveyed using the

UAV system and ground DGPS. Two stockpiles were surveyed using a LIDAR system. For stockpiles in

excess of 500 m3, the difference in volume estimates obtained from the UAV vs the ground DGPS

method were less than 2%. For the two LIDAR tests, the volume-estimate difference was less 1.5%.

Table 2 – Accuracy of Volume Estimates.

GPS Volume

m3

LIDAR Volume

m3

UAV Volume

m3

GPS Difference

m3

GPS Difference

%

LIDAR Difference

%

220.30

205.44 -14.87 -6.75 182.51

168.73 -13.78 -7.55

142.37

139.56 -2.81 -1.97 136.52

123.64 -12.88 -9.44

166.69

149.51 -17.18 -10.31 465.76

475.07 9.31 2.00

679.26

689.34 10.08 1.48 621.62

633.55 11.93 1.92

651.22 661.33 664.06 12.84 1.97 0.41

1239.12

1232.93 -6.19 -0.50 2188.53

2174.32 -14.21 -0.65

4480.61 4347.64 4407.26 -73.35 -1.64 1.37

Processing

Terrane Aerial Mapping uses Agisoft PhotoscanTM photogrammetry software to produce high-quality

orthophotos and DEM’s from the raw UAV airphotos. Delivery of a basic orthophoto, raw images and a

processing/logistics report are included with every survey. All data products are reviewed and approved

by a professional Engineer or Geoscientist (P.Eng or P.Geo) before delivery. Most common image and

GIS/CAD file-format outputs are available at the request of the client. Images can be geo-referenced in

the datum/coordinate system of choice.

Additionally, Terrane Aerial Mapping offers interpretative products such as volume-estimates,

slope/aspect maps, slope stability analysis, contours, geological interpretation, vectorization, and profile

generation. A typical processing flow-chart is shown below in Table 3.

Table 3 – Processing Flow Chart.

Input Raw

Camera Data

(JPEG images)

Input Plane GPS

photo locations

and altitude

Input Ground Control

Point Coordinates

(DGPS)

Align and mosaic

photos.

Generate

smooth DEM

Drape/texture

DEM with Photo

Mosaic

Generate 3D

model

Output

Orthophoto:

-GeoTIFF

-JPG, PNG

- KML

Output DEM:

-GeoTIFF

-ESRI ASC

- X,Y,Z

- BIL

Output 3D model:

-AGISOFT

-OBJ, WRL, DAE, PLY

- X,Y,Z

- Google Earth KMZ

- 3D PDF

- CAD DXF, FBX

QA/QC

QA/QC

QA/QC

High-Res DEM required for volume

calculation or survey applications?

Delivery of data and

processing/logistics report.

Crop to area of

interest

Re-build DEM at

high-resolution

GIS or advanced interpretive

products required?

Volume

Calculations

QA/QC

Delivery of volume estimates

QA/QC

QC

Delivery of volume estimates

Additional data products:

- Topo contours

- Geological interpretation

- Digitization to GIS vector

formats

- Slope/aspect maps

- Presentation 3-D

models/fly-through

animation

Export of data to common formats:

- GeoTIFF,JPEG, PNG, BMP

- ESRI, Mapinfo, Geosoft

- ASCII, DXF

- KMZ, 3-D PDF

QA/QC

QC

Delivery of volume estimates

Y

N

N

Y

Safety

The low mass (1.1 kg) and speed of the UAV limit the kinetic energy to 150 J. This ensures that if the

system is involved in a collision, that neither the UAV nor the object is harmed. The system has been in

use since 2006 and has an exceptional safety record. Accident statistics collected by the manufacturer

are shown in Tables 4 and 5. Of 22 reported crashes/incidents, two operator injuries occurred from

propeller cuts. No injuries to 3rd parties or property damage from UAV-related incidents have been

reported.

Table 4 – Accident causes/incidents.

Accident Cause Number

Pilot Error 8

Interference 8

Airframe /Mechanical 3

Electronics 2

Weather 1

Table 5 – Accident Incident Outcomes

Accident Cause Number

Operator personal injury (propeller cuts on fingers)

2

3rd party personal injury 0

Property damage 0

The on-board flight computer/autopilot system will return the aircraft to a control-station circle in the

event of loss of radio contact or exceeding dimensions of a 1km “virtual fence”.

Terrane Aerial Mapping will develop a formal Emergency Response Plan (ERP) for every flight mission

and will meet or exceed all Transport Canada regulatory and client safety/environmental standards.

References

Vallet, J., Panissod, F., Strecha, M., Tracol, M. 2011. Photogrammetric performance of an ultra light

weight swinglet “UAV”. International Archives of the Photogrammetry, Remote Sensing and

Spatial Information Sciences, Vol. XXXVIII, ISPRS ICWG I/V UAV-g (unmanned aerial vehicle in

geomatics) conference, Zurich, Switzerland. 6p.