ASIA GEOSPATIAL FORUM 2011 Application of LIDAR Technology for GCP

Application of LIDAR Technology for GCP Determination in Papua Topographic Mapping Scale
1:50.000
by
Wildan firdaus, Aldino Rizaldy and Aji Putra Perdana
BAKOSURTANAL – Center for Topographic Base Mapping, Cibinong, Indonesia
E-mail: ini.wildan@gmail.com
Abstract
LIDAR (Light Detection and Ranging) technology application in various field of science has became
very popular nowadays. One of LIDAR application that was study by Bakosurtanal is the use of LIDAR
for determining GCP in aerial photographs. The GCP from LIDAR data (point cloud) was transferred
to above aerial photograph by pricking the diapositif which will be observe. In the end, the GCP point
which pricked on the above aerial photographs is also clearly visible on the LIDAR image. The result
of GCP precision show rms x = 3.500 m, rms y = 4.383 m dan rms z = 0.866 m fulfill the specification
from Bakosurtanal which is rms (x,y) < 5m dan rms z < 2 m. This proves that the LIDAR technology
can be used in the process of determining the GCP on aerial photographs.
1. Introduction
In order to Papua topographic mapping 1:50,000 scale, old aerial photograph that do not have the
ground control points or GCP (Ground Control Point) are used. Aerial Photograph used with
consideration of topography of Papua is almost unchanged during last 20 years, , it was a good idea
to use the existing heterogeneous photos for topographical mapping. The problems that arise in a
series of technical work is how the procurement of GCP and to put the ground control in the
photoblock for the aerial triangulation (AT) process.
The solution was taken to this problem is to use LIDAR technology which with ability to map very
large areas in a short time with a sweep of a laser scanner integrated in the system emits laser dots
on its path area with a high intensity and density.
LIDAR (Light Detection And ranging) is the latest remote sensing technology to map the elevation of
the earth's surface with a high vertical accuracy [Sun, et al., 2003; Lefsky, et al., 2005; Hofton, et al.,
2006; Chen, 2007; Simard , et al., 2008]. In practice, the standard horizontal and vertical accuracy of
LIDAR (at 1σ) typically range from 0:05 m and 0.2 m for height and between 0.2 m and 1.0 m for the
ASIA GEOSPATIAL FORUM 2011
position (with consideration flight height above 2000 m height from ground level) [Beradlin, JA, Blais
, F., Lohr, U., 2010].
In LIDAR, there are 3 instruments that work together, which is:
1. GPS (Global Positioning System), satellite-based positioning systems, to produce coordinates
data (X, Y, Z) at the time of survey.
2. INS (Inertial Navigation System), a set of navigation tools that use computers, motion
sensors and rotation sensors that generate rotational movement data of the vehicle flight
(pitch, roll and yaw).
3. Laser Scanner, a tool that records every form of real-world objects that are scanned,
generating range data from the vehicle flight to the surface that are surveyed.
GPS observation methods commonly used in LIDAR applications using GPS Kinematic with PPP
(Precise Point Positioning), a GPS post-processing method. PPP is the development of processing
techniques that we know as the differential processing.
PPP use precise orbit and also the GPS clock correction, which is computed by the IGS (International
GNSS Service). Satellites orbit and GPS clock correction is downloaded in data packets every 10 days.
By using L1/L2 GPS receiver, the data that are recorded can be made atmosphere model to data to
eliminate the ionosphere error.
One the advantage using this method is the practicality of kinematic measurements. When
Kinematic measurements is conducted, GPS Reference is not required.
To be able to utilize the PPP, there are requirements that must be met:
 Using Receiver L1/L2
 Long observation of at least 1 hour. Longer observations are better
 Internet connection required to get the precise orbit of GPS satellites and also the GPS clock
corrections
 Can use GPS or GLONASS
According to GrafNav (one of the LIDAR survey service providers) the overall accuracy of the PPP
about 10 cm to 20 cm. For surveys that do not require very high accuracy level that is acceptable and
for aerial survey for corridor mapping along flight paths that require very long baseline, the PPP is an
ideal solution.
2. Methods
The following section describes the whole processing chain used in this research which is collecting
Ground Control Coordinate (GCP) from LIDAR survey to do Aerial Triangulation (AT) in old aerial
photographs. According to the flowchart below, it divided into two major workflow: LIDAR workflow
and AT workflow coverage.
ASIA GEOSPATIAL FORUM 2011
Aerial Photo
(diapositive & paper print)
Satellite Imagery
Medium Resolution
Diapositive
Scanning
AT
workflow
Georeferencing
GCP
selection
LIDAR Survey Path
Planning
LIDAR
workflow
LIDAR Data
Acquisition
Minor Point
selection
Pricking and Point
Measurement
List of GCP Coordinate
in Image System
(micron)
LIDAR Data
Processing
Pricking dan Point
Measurement
List of Minor Point
Coordinate in Image
System (micron)
Ortho Rectified Image (ORI)
Digital Surface Model (DSM)
Digital Terain Model (DTM)
List of GCP Coordinate
in Terrain System
(meter)
Fig. 1. Flowchart of the research
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Bundle Adjustment
Calculation
2.1. LIDAR work
2.1.1. Preparation
Aerial photo need to be scanned to mosaic it per 1:50.000 map sheet. This make easily to numbered
a GCP based on map sheet number. Satellite imagery need to geometry corrected (georeferencing),
it will be use in flight planning. To make LIDAR flight planning, it must be based on GCP distribution.
Then GCP distribution must be determined before and according to AT rules: it distribute along
perimeter area of AT block and it must be places every minimum of 6 photo base.
Fig. 2. Photo Frame on Working Map Sheet (Survey Area)
2.1.2. Flight Planning
Flight line is a corridor 500 – 1000 meter width and have a distance about 10 – 15 km each other.
Flight line planning according on objects which will be use for GCP, so it shouldn’t on a straight line.
It may a zig zag line, following to objects. Flight line can be Eastern – Western or Southern –
Northern. Then it drawn in satellite imagery and become flight line map.
ASIA GEOSPATIAL FORUM 2011
2.1.3. LIDAR Data Acquisition
LIDAR Data Acquisition implemented using airborne and LIDAR devices which correspond to
technical specification. Data acquisition held on a corridor that have 500 – 1000 meter width and
divided into 500 x 500 meter tiles sized. Cloud coverage must be less than 5 % on each lines.
Required LIDAR data accuracy is 30 – 50 cm (planimetry) and 15 – 25 cm (height). LIDAR survey
generate point cloud with density 30 – 50 cm.
All devices installed on aircraft correctly and the aircraft must flight for flight planning calibration
before and after survey in every day. This LIDAR survey use GPS/IMU to determine position and
orientation of LIDAR device accurately. Before flight, GPS/IMU must be checked it work correctly.
2.1.4. LIDAR Data Process
GPS/IMU data processed to determine position and orientation LIDAR device accurately. Then it
used (jointly with calibration data) in calculation of LIDAR data. The results is point cloud which have
correct position. Because this data is very large, it divided into 500 x 500 meter tile sized.
Point clouds data is Digital Surface Model (DSM). It must be converted to Digital Terain Model (DTM)
to know terain coordinate which will be use for height coordinate of GCP. Then Ortho Rectified
Image must be generated to be used in planimetry coordinate of GCP.
2.1.5. GCP Coordinates
In the end of LIDAR workflow coverage it obtained list of GCP coordinates in terrain system (meter)
which will be use for Bundle Adjustment calculation.
2.2. Aerial Triangulation (AT) work
2.2.1. Preparation
GCP selection is based on objects which will be used for control point. This object must a clear and
well identified object such as cross junction, runway, or bend river. It must be visible at aerial photo
and ORI bothly. Then it marked on paper print. GCP numbering based on map sheet to easily
identification. Minor point preparation include planning of selection and identification of minor
point in stereomodel. Minor point must follow AT rules, eg. every stereomodel there is minimum 6
minor points.
2.2.2.Pricking and Point Measurement
GCP and minor points pricked on diapositive using point transfer device, eg Wild PUG4 which has 60
micron accuracy. Point measurement measures GCP and minor point in image system coordinate
(micron). The results is list of GCP and minor point coordinate in image system. It will use next on
Bundle Adjustment calculation.
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2.2.3. Bundle Adjustment
This calculation need three data: GCP coordinates in terrain system, GCP coordinates in image
system, and minor point coordinates in image system. Bundle Adjustment calculate using Least
Square Adjustment and Collinier Condition principle. The result is exterior orientation parameter for
every photo and all point with adjusted coordinates, one of them can use as input data for
stereoplotitng process.
3. Result
3.1. LIDAR Data Acquisition and Processing
Result from the LIDAR data process is DSM (Digital Surface Model) and then it is generated to
become DTM, this is where we get height points that we will move onto above the photo block. In
addition, from this survey activity also obtained the digital aerial photograph along the corridor
mapping to help identify the point of GCP.
Fig. 3. DSM from LIDAR data
Fig. 4. DTM from LIDAR data
3.2 Pricking
Pricking mean point transfer, in this case transfer of the Ground Control Point (GCP), which has been
selected from the LIDAR image, to the Aerial Photography Image, then performed pricking on aerial
photographs diapositif.
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GCP Details in river
branch on LIDAR image
Image LIDAR File number :
100827B-17527-311-274.ecw
Fig. 5. GCP identificationon on LIDAR image
Same GCP Detail in river branch
on Aerial Photograph Image
33104304
Fig. 6. GCP identificationon on Aerial Photograph image
Aerial Photograph Image Run 160A, Film Number F131428, Photo Number 13, Counter Number 374
(R160A-F131428\13-374)
ASIA GEOSPATIAL FORUM 2011
Pricking process use points transfer tool, in this work were used two (2) Point Unit Transfer Device Wild PUG4.
Fig.7. Point Transfer Device – WILD PUG4
Furthermore, a point which had been pricked is marked with special colored pencil (dermatograph
pencil) by give a circle or triangle symbol and given numbering in accordance with the existing
number at GCP determination phase.
Fig. 8. GCP distribution on photo block.
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GCP pricking are done on each diapositif which previously identified in selection and numbering
Ground Control Point (GCP) phase. Has been pricked as many as 800 (eight hundred) points of GCP.
3.3 Aerial Triangulation
From Aerial Triangulation (AT) and then Bundle Adjustment calculation, it delivered some results:
3.3.1 RMS GCP
RMS X : 2.867 meter
RMS Y : 3.102 meter
RMS Z : 0.864 meter
From AT technical spesification released by Bakosurtanal, it required :
RMS X,Y < 5 meter
RMS Z < 2 meter
It mean the GCP points which are resulted in this work able to fulfill Bakosurtanal specification.
3.3.2 Minor Point RMSE
RMS X : 28.23 micron
RMS Y : 20.17 micron
From AT technical spesification released by Bakosurtanal, it required RMS < 25 micron
If we check RMS X, it has worse accuracy than requirement while RMS Y has better. It maybe happen
when in minor point measurement phase, it measure not very accurate.
3.3.3 Sigma Naught
Sigma Naught : 36.98 micron
From AT technical spesification released by Bakosurtanal, it required sigma naught ≤30 micron
Sigma naught from Bundle Adjustment calculation has worse accuracy than the requirement. It
happen because when measure some points, it measure not very accurate. Then it delivered worse
accuracy. But this sigma naught value can be better with re-measurement at point with big residual.
4. Discussion
The result show that from the point clouds of LIDAR data can be generate to become DSM and DTM.
The LIDAR point that used as GCP have good quality of precision (rms) that fulfill the specification
from Bakosurtanal. Methodology for collecting GCP from Airborne LIDAR survey which is used in this
study, able to meet the requirement.
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Aerial Photographs data which used were captured in 1990-1996, has undergone many changes in
detail compared with LIDAR image which were captured in 2010.
Natural conditions in the work area is relatively densely forested, make it difficult to identify the
details, so the selection of a point more emphasis on the details of rivers, river branch intersection
and crossroads.
5. Conclusion
LIDAR data has a very high intensity and density. LIDAR technology make pricking process easier
because LIDAR produce big amount quantity of spatial points.
The accuracy of minor point measurement is vital the whole process phase. Measurement which not
very accurate will deliver worse accuracy. One of the possibility of inaccurate measurement in Aerial
Triangulation process is the used of GCP from current survey on old aerial photographs which the
natural condition may have changes.
The use of digital image, as a result from digital photogrammetry camera which is integrated with
LIDAR system, is very helpful in points identification process and transfer the LIDAR point to above
the photo block.
Quality of GCP that are generated from LIDAR data is relatively good. The result of GCP precision
show rms x = 3.500 m, rms y = 4.383 m dan rms z = 0.866 m fulfill the specification from
Bakosurtanal which is rms (x,y) < 5m dan rms z < 2 m. This proves that the LIDAR technology can be
used in the process of determining the GCP on aerial photographs.
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Paper Reference No. : PN – 74
Title of the paper : Application of LIDAR Technology for GCP Determination in Papua
Topographic Mapping Scale 1:50.000.
Name of the Presenter : Wildan Firdaus, ST
Author (s) Affiliation : BAKOSURTANAL
Mailing Address : BAKOSURTANAL, Gedung R, Pusat Pemetaan Dasar Rupabumi
JL. Raya Jakarta – Bogor km.46 Cibinong 16911
West Java-Indonesia
Email Address : ini.wildan@gmail.com
Telephone number (s) : +6281221780081
Author(s) Photograph:
Brief Biography (100 words):
Name
: Wildan Firdaus, ST
Place of Birth : Bandung, 25th May 1985
Education
: S1 Degree in Geodesy and Geomatics Engineering, Faculty of Earth Science
and Technology, Bandung Institute of Technology (ITB) (2008). Undergraduate Thesis :
“System and Application of Laser Scanner, Case Study: Zakum Offshore Platform
Measurement”.
Position
: I have been worked in various field of work, in oil company JOB
PERTAMINA-TALISMAN (OK) Ltd. as Topography QC (March – July 2008), in survey and
mapping consultant PT Geoindo as surveyor (Oct 2008 – Oct 2009). Now I’m working in
Center for Topographic Base Mapping-BAKOSURTANAL since December 2009 till now.
ASIA GEOSPATIAL FORUM 2011