วารสารวิจัยและพัฒนา มจธ. ปีที่ 43 ฉบับที่ 2 เมษายน - มิถุนายน 2563

133

Evaluation of UAV Photogrammetric Accuracy for Mapping of Open Dump
Based on Variation of Image Overlaps
Abhisit Bhatsada1, Sirintornthep Towprayoon2*, Savitri Garivait2, Komsilp Wangyao3*,
King Mongkut’s University of Technology Thonburi, Bangmod, Thungkru, Bangkok 10140
Centre of Excellence on Energy Technology and Environment, PERDO, Bangkok 10140

Theera Laphitchayangkul4,

King Mongkut's University of Technology Thonburi, Bangmod,Thungkru, Bangkok 10140

Tomonori Ishigaki5

National Institute for Environmental Studies, Onogawa, Ibaraki, Japan 305-0053

and Chart Chiemchaisri6

Kasetsart University, Lat Yao, Chatuchak, Bangkok, 10900* Corresponding Author: sirin@jgsee.kmutt.ac.th, komsilp@jgsee.kmutt.ac.th
1Master’s Student, The Joint Graduate School of Energy and Environment
2
Associate Professor, The Joint Graduate School of Energy and Environment
3
Research Associate, The Joint Graduate School of Energy and Environment.
4
Assistant Professor, Faculty of Engineering.
5
Researcher, Center for Material Cycles and Waste Management Research.
6
Associate Professor, Faculty of Engineering.

Article Info

Abstract

Article History:
Received: September 27, 2019
Revised: March 10, 2020
Accepted: April 13, 2020

Urbanization in developing countries has led to an increase in both quantified
amount of municipal solid waste (MSW) generation and final disposal. While
many countries are utilizing open dumping to dispose MSW, such a practice
can cause environmental, social, and economic problems. Accurate spatial
data in the form of mapping is necessary for construction and proper management of a disposal site as well as for systematic operation, site maintenance,and monitoring of the site. Although unmanned aerial vehicle (UAV) has widely
been used in many survey applications, UAV has not yet been applied to thework related to open dumpsite. The aim of this study was to evaluate theaccuracy of open dump mapping with different image overlaps for setting basic
and standard UAV flight information. Ground sampling distance values were
set to 5 cm/pixel, while flight configurations were varied from 80% to 90%
and 75% to 90% for frontal and side overlaps, respectively. Root mean squareerror (RMSE) was used to represent the accuracy of the measurement. Ten
ground control points for geo-referencing and 26-28 check points for accuracy
evaluation were utilized. The results were classified based on the accuracy
class as per the American Society for Photogrammetry and Remote Sensing
standard. The best results were obtained when using 80% frontal overlap and
75% side overlap; these values resulted in the lowest RMSE on both horizontal
and vertical coor-dinations for open dump mapping.

Keywords:
Open Dumping / Mapping /UAV Photogrammetry /Flight Configuration / Drone

134วารสารวิจัยและพัฒนา มจธ. ปีที่ 43 ฉบับที่ 2 เมษายน - มิถุนายน 2563

การประเมินความถูกต้องจากการรังวัดด้วยอากาศยานไร้คนขับส�ำหรับท�ำแผนที่บ่อขยะ
แบบเทกองด้วยการก�ำหนดค่ารูปแบบการบินถ่ายภาพ
อภิสิทธิ์ ภาสดา1 สิรินทรเทพ เต้าประยูร2*สาวิตรี การีเวทย์2 คมศิลป์ วังยาว3*มหาวิทยาลัยเทคโนโลยีพระจอมเกล้าธนบุรี บางมด ทุ่งครุ กรุงเทพฯ 10140
ศูนย์ความเป็นเลิศด้านเทคโนโลยีพลังงานและสิ่งแวดล้อม ส�ำนักพัฒนาบัณฑิตศึกษาและวิจัย
ด้านวิทยาศาสตร์และเทคโนโลยี กรุงเทพฯ 10140

ธีระ ลาภิศชยางกูล4มหาวิทยาลัยเทคโนโลยีพระจอมเกล้าธนบุรี บางมด ทุ่งครุ กรุงเทพฯ 10140

Tomonori Ishigaki5สถาบันวิจัยสิ่งแวดล้อมแห่งชาติ โอโนกาวา สึกุบะ อิบารากิ ญี่ปุ่น 305-0053

และ ชาติ เจียมไชยศรี6มหาวิทยาลัยเกษตรศาสตร์ ลาดยาว จตุจักร กรุงเทพฯ 10900* Corresponding Author: sirin@jgsee.kmutt.ac.th, komsilp@jgsee.kmutt.ac.th1นักศึกษาปริญญาโท บัณฑิตวิทยาลัยร่วมด้านพลังงานและสิ่งแวดล้อม
2รองศาสตราจารย์ บัณฑิตวิทยาลัยร่วมด้านพลังงานและสิ่งแวดล้อม
3นักวิจัย บัณฑิตวิทยาลัยร่วมด้านพลังงานและสิ่งแวดล้อม
4ผู้ช่วยศาสตราจารย์ ภาควิชาวิศวกรรมโยธา คณะวิศวกรรมศาสตร์
5นักวิจัย Center for Material Cycles and Waste Management Research
6รองศาสตราจารย์ ภาควิชาวิศวกรรมสิ่งแวดล้อม คณะวิศวกรรมศาสตร์ข้ อ มู ล บ ท ค ว า มบ ท คั ด ย่ อประวัติบทความ :รับเพื่อพิจารณา : 27 กันยายน 2562
แก้ไข : 4 มีนาคม 2563
ตอบรับ : 13 เมษายน 2563

การขยายตัวของชุมชนเมืองในประเทศที่ก�ำลังพัฒนาส่งผลให้ปริมาณขยะมูลฝอยและการฝังกลบ
ขยะมูลฝอยมีมากขึ้น ประเทศส่วนใหญ่จัดการขยะเหล่านี้ด้วยการน�ำไปก�ำจัดที่บ่อขยะแบบเทกอง
กลางแจ้ง ซึง่ ท�ำให้เกิดผลกระทบต่อสิง่ แวดล้อม สังคม และเศรษฐกิจ ในการสร้างและบริหารจัดการ
บ่อขยะอย่างเหมาะสม ซึ่งประกอบไปด้วยขั้นตอนของการด�ำเนินการ การซ่อมบ�ำรุง และการตรวจ
สอบอย่างเป็นระบบนั้น จ�ำเป็นต้องมีข้อมูลเชิงพื้นที่ ซึ่งแสดงในรูปแบบของแผนที่ ที่มีความถูกต้อง
แม้วา่ อากาศยานไร้คนขับจะถูกน�ำมาใช้เพือ่ การส�ำรวจอย่างแพร่หลาย แต่ยงั ไม่มกี ารน�ำมาใช้สำ� รวจบ่อขยะแบบเทกองกลางแจ้งมาก่อน งานวิจัยนี้จึงมีวัตถุประสงค์เพื่อประเมินผลความถูกต้องของ
การท�ำแผนที่บ่อขยะแบบเทกองกลางแจ้งด้วยการก�ำหนดการซ้อนทับภาพที่แตกต่างกัน ซึ่งท�ำให้
ทราบรูปแบบการบินถ่ายภาพที่เหมาะสมส�ำหรับเป็นแนวทางมาตรฐานของการรังวัดท�ำแผนที่ด้วย
อากาศยานไร้คนขับในบ่อขยะแบบเทกองกลางแจ้งต่อไป งานวิจัยนี้ก�ำหนดค่า Ground Sample
Distance เท่ากับ 5 ซม./จุดภาพ ก�ำหนดรูปแบบการบินถ่ายภาพให้มีการซ้อนทับด้านหน้าและการ
ซ้อนทับด้านข้างอยู่ที่ 80% ถึง 90% และ 75% ถึง 90% ตามล�ำดับ ประเมินความคลาดเคลื่อน
เชิงต�ำแหน่งด้วยค่า Root Mean Square Error (RMSE) มีการวางจุดควบคุมภาพ จ�ำนวน 10 จุดและจุดตรวจสอบ จ�ำนวน 26-28 จุด ทั้งนี้ เปรียบเทียบการประมวลผลตามมาตรฐาน American
Society for Photogrammetry and Remote Sensing จากการศึกษา พบว่า รูปแบบการบิน
ถ่ายภาพที่ให้ค่าความถูกต้องสูงสุดส�ำหรับการท�ำแผนที่บ่อขยะแบบเทกองกลางแจ้ง คือ การบิน
ถ่ายภาพด้วยการซ้อนทับด้านหน้าที่ 80% และซ้อนทับด้านข้างที่ 75% ซึ่งให้ค่า RMSE น้อยที่สุด
ทั้งในแนวระนาบและแนวดิ่ง

ค�ำส�ำคัญ :บ่อขยะแบบเทกอง / การท�ำแผนที่ /การรังวัดด้วยอากาศยานไร้คนขับ /การก�ำหนดรูปแบบการบิน / โดรนวารสารวิจัยและพัฒนา มจธ. ปีที่ 43 ฉบับที่ 2 เมษายน - มิถุนายน 2563

1. INTRODUCTION

Urbanization and industrialization of many developing countries have led to an increasing amount ofmunicipal solid waste (MSW) generated and sent to
final disposal sites. Open dumping is the most popularmethod for the disposal of MSW in developing countries due to low operating costs and skilled personalrequirements [1-2]. Nowadays, the amount of waste
has increased, so there must be more space to support the disposal. Correspondingly, it affects the environment, ecosystem community and real estate
nearby [3-5]. Therefore, the operation and maintenance of open dumps are important tasks for solid
waste disposal site management. The waste that isdegraded in open dumps can change its chemical,
biological, and physical characteristics, which producesleachate, gases and materials productions [6-7]. However, this degraded waste can be processed back into
recyclable materials that have economic value. The
study of changes in open waste disposal areas provides important information for social, economic andenvironmental assessments as well as social impacts
from the discharge of leachate, gas, and materials.
[8-9].
The tools used to identify the change of open
dumping are spatial information. Map can be used formonitoring, tracking and planning the operation as
well as planning for closure and rehabilitation of open
dump. Open dump monitoring needs to monitor theamount of waste, waste height, slope of dumped
waste, overflow of leachate, and litter problem. Open
dump mining recovers materials from disposed waste,especially plastic; this mining needs to know theamount of waste that can be converted into Refuse
Derived Fuel (RDF), which leads to estimation ofpotential energy recovery [10].
Topographic map by land surveying is necessary

135

for estimating the amount of disposed waste. Normally,surveyors use various equipments for mapping, e.g.
total stations, theodolites, Global Navigation Satellite
System (GNSS) receivers, which are used for collecting
the three-dimensional (3D) positions of points anddistances data. However, these methods are the direct
measurements that need to set up survey instrumentsin the field. In actual conditions, surveying equipment
on non-compact waste is very complicated and leads
to severe uncertainty data. In addition, final disposalsite is a hazardous area because wastewater, toxic
gases, and dust can affect surveyors. Thus, traditional
survey methods do not only cause harm to surveyors
but it is also difficult for field working.
Nowadays, Unmanned Aerial Vehicle (UAV) or drone
technology has been used in manifold fields such as
terrain mapping, construction industry, environmental
monitoring, precision agriculture [11-12]. For mapping
process, UAV has been operated with geospatial information and used for producing maps with a lowcost option. The strength of UAV photogrammetry formapping, i.e., capability, flexibility, and high qualityof photo acquisition, can produce a 3D model by
structure-from-motion (SfM) method [13-15]. Kristen
Cook (2017) and Ewertowski et al. (2019) defined themeaning of the SfM as a generation of photogrammetric technique that automatically solve the geometry of scene, camera positions, and the orientation
without requiring a priori specification of a networkin term of 3D positions. [16-17]. Many factors that
affect accuracy of maps and 3D models obtained by
Unmanned Aircraft System (UAS) photogrammetry
are flight altitude, terrain morphology, number ofground control points (GCPs), frontal and side overlaps,
and weather condition [18].
This study aims to evaluate the photogrammetricmapping accuracy of 3D models and orthophotos

136วารสารวิจัยและพัฒนา มจธ. ปีที่ 43 ฉบับที่ 2 เมษายน - มิถุนายน 2563

derived from UAV Photogrammetry, based on the Table 1 Flight configurations (FC)variation of frontal overlap and side overlap in open
dump mapping in order to increase mapping accuracyof disposal operation.

2. MATERIALS AND METHODS
2.1 Study site					 The studied site is open dump in Muang
district, Nakhon Pathom province, Thailand (13°52'03"N
100°02'37"E), as presented in Fig.1. This site covers
4.78 hectares (0.0478 km2). Currently, this studied
site is collected the MSW from 19 municipalities. The
open dump mapping was conducted from January to assessment.
					 According to American Society for PhotoFebruary 2019.
grammetry and Remote Sensing (ASPRS) Positional
2.2 Image acquisition					 This study generated images from a low-cost Accuracy Standards for Digital Geospatial Data (2014),
rotatory wing UAV with four rotors (DJI Phantom 3 the number of static 3D checkpoints in Non-vegetatedprofessional). This UAV has an built-in digital camera, Vertical Accuracy (NVA) is at least 20 points based on
Sony EXMOR 1/2.3" CMOS camera with lens and fixed a project area with less than 500 m2 [19].
focal length of 20 mm The resolution of the camera 					 The 3D coordinates of positions at 10 GCPs
sensor was 12.0 megapixels (4000×3000 megapixels) and 28 CPs for geo-referencing and accuracy assessment in the image processing were measured before
equipped with a gimbal.
					 The flight height was set at 114 m above the UAV flight by GNSS receptor working in Real-timehome point level, covered the surface of 390×250 m kinetic (RTK) mode. Both rover and base GNSS receieach photo and it is equivalent to the Ground sam- vers were Hi-target V100 system. For RTK measurepling distance (GSD) of 5.0 cm/pixel. All flights were ments, these dual-frequency geodetic instruments
set as a single grid pattern. All flight plans in this have a manufacturer’s stated accuracy specification
study were automatically photographed above the of ±8 mm +0.5 ppm horizontal RMS and ±15 mm +0.5 ppm vertical RSM. However, GCP and CP targets
study area by the Pix4Dcapture application.
					 To address the objectives, this study varied must have appropriately designed for minimizing error
the overlapping between 80-90% and 75-90% for during geo-referencing and accuracy assessment
frontal and side overlap, respectively. Six flight con- processes. The dimension of GCP was 1.20×1.20 m,
figurations were used to determine a photogramme- which had resembled a chequered block sheet. The
tric project (Table 1). The sets of 10 GCPs and 28 dimension of CP was 0.40×0.40 m, which had a black
checkpoints (CPs) were placed in the studied area circle with a diameter of 25 cm inside the orange(Fig.1). The GCPs are used to produce photogram- square sheet. The figure of GCP and CP are shown inmetric output, likewise the CPs are used for accuracy Fig.2.

วารสารวิจัยและพัฒนา มจธ. ปีที่ 43 ฉบับที่ 2 เมษายน - มิถุนายน 2563

137

Figure 3 3D reconstruction from UAV image data
Figure 1 Location of the study area and theposition of GCPs and CPs with orthoimage

the Dense Point Cloud”, which is estimated camera
positions, calculating of several X,Y,Z points in orderto accurately create the model of processing. Finally,
the inspection of textured model, which is important
for a precise marker of GCP and CP placement generating into orthophoto, is conducted in this study,
as shown in Fig.3. [18].

2.4 Accuracy assessment

Figure 2 The GCP (a) and CP (b) targets

2.3 Image processing					 The image processing was implemented byusing the software package Agisoft PhotoScan Professional version 1.4.4. This software classified as the
SfM algorithm. Agisoft Photoscan software was used
for processing the photos, which illustrates the possibility of the generation of georeferenced point
clouds, digital surface elevation models, and mosaiced
image for geographic information system data in orderto build a layer of mapping on the image processing.
Aligning Photos, the first step of image processing, isperformed to tie the images together in an automatedimage correlation process in order to create a sparse
point cloud. The next step is “Optimizing the PhotoAlignment”; it is used for performing photogrammetricleast squares bundle adjustment. The next is “Build					 The spatial accuracy of this study was evaluated based on the positions of the CP that wereobtained from the RTK-GNSS and the positions generated by the 3D model. The accuracy of X, Y, andZ axes were evaluated in this study by using Root
Mean Square Error (RMSE) for determining the accuracy
classes.
					 The accuracy of all photogrammetric projects
were evaluated by typical RMSE formulation, following
to Martínez-Carricondo et al. (2018).
RMSEX =

(1)

RMSEY =

(2)

RMSEr 		 =(3)RMSEZ =

(4)

RMSET =

(5)

138

วารสารวิจัยและพัฒนา มจธ. ปีที่ 43 ฉบับที่ 2 เมษายน - มิถุนายน 2563

Where:- n is the number of CPs tested for each project.
- XOi and YOi are the X and Y coordinates,			 respectively, measured in the orthophoto for			 the ith CP.
- XGNSS and YGNSSi are the X and Y coordinates,			 respectively, measured with GNSS for the ith CP.
- ZOi is the height in the ith CP, derived from the			 digital surface model (DSM), taking into account			 its coordinates X and Y, measured on the			 orthophoto.
- ZGNSSi is the Z coordinate of the ith CP measured
			 with GNSS.

the Z direction (Elevation).
The results of the horizontal accuracy of both
GCPs and CPs in each flight configuration are presented in Fig.4. The results of these flight configurations
were based on the ASPRS standard Version 1.0November 2014. This standard defines geolocation
accuracy to geospatial products [19]. This standard
recommends the use of orthoimage in three categories
according to their orthoimage RMSEX and RMSEY
values. When these values do not exceed 1-pixel,
the orthoimagery can be used in the highest accuracy
work. If these values do not exceed 2-pixel, thisorthoimagery can be used in standard mapping andgeographic information system (GIS) work. On the
3. RESULTS AND DISCUSSION
other hand, if these values are equal to or greater
		Waste quantity and settlement can be calculated than 3-pixel, the orthoimage can be only used infrom 3D mapping by X, Y and Z coordination. The visualization and less accurate work [19].
total station is used as a traditional survey in orderto map and study the ground settlement. Thismethod obtained the measurement of an accurate
position [20]. However, this method has some limitations for implementation on open dump site. The
accuracy of mapping by UAV photogrammetry should
be studied because UAV photogrammetry is anappropriate method for open dump mapping.
The GCPs and CPs were used to investigate accuracyof the project; the independent accuracy of georeferencing was checked by GCPs, and project accuracy was checked by CPs [21]. Both parameters
are represented in terms of RMSE of horizontal andvertical positions. RMSEX is the standard deviation of
the horizontal linear RMSE in the X direction (Easting).
RMSEY is the standard deviation of horizontal linear
RMSE in the Y direction (Northing). RMSEr is thehorizontal linear RMSE in the radial direction that Figure 4 RMSEX and RMSEY of GCPs and CPs forincludes both X- and Y-coordinate errors. RMSEZ iseach flight configuration
the standard deviation of the vertical linear RMSE inวารสารวิจัยและพัฒนา มจธ. ปีที่ 43 ฉบับที่ 2 เมษายน - มิถุนายน 2563

From Fig. 4, the RMSEX of GCPs were lower than
1 pixel (5 cm) in all flight configurations except FC2.
The RMSEY of GCPs in FC2 and FC4 were lower than
1 pixel or 5 cm. The RMSEY of GCPs in FC1, FC3, FC5,
and FC6 were between 1 and 2 pixels. The results
showed that the FC4 had the best geo-referencing inthis study.
The RMSEY of CPs was found that only RMSEX of
CPs in FC1 had lower than 1 pixel. RMSEX of CPs in
FC2-FC6 was between 1 and 2 pixels. The RMSEY of
CPs in CF1 was between 1 and 2 pixels. However, in
FC2 to FC6, the RMSEY of CPs were more than 2 pixels.
According to the ASPRS standard (2014), it was foundthat the FC1 can be the recommended use in standard
mapping and GIS work. For the cases of (FC2 to FC6),
it can be recommended to be used only in thevisualization and less accurate work.

Figure 5 RMSEr of GCPs and CPs for each flight
configuration

139

Fig.5 presents the horizontal linear RMSE in radial
direction, which is shown in terms of RMSEr. The
results of GCPs of all flight configurations were
between 6.30-7.95 cm. RMSEr of FC1 gave the lowest
value (7.25 cm). In contrast to the FC2 to FC6, thevalues of RMSEr of CPs were greater than FC1, whichwere between 12.90-16.25 cm.
The ASPRS standard also gives the recommendation
for the comparison of RMSEZ result with verticalaccuracy criteria. [19]. This study assessed verticalaccuracy in a non-vegetated terrain condition, which
is suitable for the open dump. The vertical accuracy
for the RMSEZ of CPs in FC1, FC3, FC4, and FC6 canbe defined as 5 cm-vertical accuracy class (Fig.6).
The RMSEZ of CPs in FC2 and FC5 can be defined as
10 cm and 15 cm-vertical accuracy class, respectively.
The RMSEZ of GCPs in FC1–FC4 also provided an
accurate geo-referencing in vertical accuracy whichshowed the RMSEZ below 5 cm In addition, the 3Dmodel process is referred to accurately position of
RMSEZ generated into a digital elevation model(DEM), as shown in the Fig.7.
The overall of horizontal and vertical accuracies
are presented in term of RMSET (Fig.8). The range of
RMSET of GCP in FC1-FC6 was between 1.41–2.87
pixels. The lower RMSET of GCP was in the FC1 andthe higher RMSET of GCP was in the FC5. The rangeof RMSET of CP in FC1-FC6 was between 1.55–3.86
pixels. The lower RMSET of CP was in the FC1 andthe higher RMSE of CP was in the FC5. The horizontal
and vertical accuracy according to the ASPRS 2014
standard and their equivalent to map scale in ASPRS
1990 standard are summarized as shown in Table 2.

140วารสารวิจัยและพัฒนา มจธ. ปีที่ 43 ฉบับที่ 2 เมษายน - มิถุนายน 2563

Figure 6 RMSEZ of GCPs and CPs for each flight
configuration

Figure 8 RMSET of GCPs and CPs for each flight
configuration

Table 2 Summary of accuracy in all flight
configurations

Figure 7 The digital elevation model (DEM)
constructionวารสารวิจัยและพัฒนา มจธ. ปีที่ 43 ฉบับที่ 2 เมษายน - มิถุนายน 2563

4. CONCLUSIONS		The UAV photogrammetry, which is a disruptive
methodology, was implemented in this study. The
othomosaic maps and 3D models for open dump
mapping were successfully generated based on 6
flight configurations that varied in frontal and side
overlap. The images were captured by the low-cost
UAV and processed by SfM software. This study showsa considerable advantage of UAV photogrammetry
over the traditional survey method at open dumpsite. Based on the analysis part, each flight configuration contributed to different errors in terms ofhorizontal and vertical positions. The RMSE analysis
showed that flight configuration at 80% frontal overlap and 75% side overlap gave the best results for
RMSEX and RMSEY within 7.5 cm. as well as RMSEZ
within 5 cm. Thus, this flight configuration can besuggested as the recommended UAV photogrammetry
practice for the mapping at the open dump. However,
the accuracy of mapping does not only depend on
flight configuration but also depends on the appropriate GCP configuration of both numbers and alignment. In further study, the appropriate GCP configuration should be investigated for finding the minimum
GCP number to ensure level of accuracy with themost appropriate and feasible facility.

5. ACKNOWLEDGMENT

		This study is supported by the National ResearchCouncil of Thailand (NRCT) for the expenses in orderto achieve the study. We would like to thank the
Nakhonpathom Municipality for providing the opportunity to gather information in the studied site. In
addition, we would like to thank the lecturer andstudents from the Department of Civil Engineering,
King Mongkut's University of Technology Thonburithat provided the advice and supported this study.

6. REFERENCES

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