CHAPTER ONE
1.0
INTRODUCTION
Surveying and geo-informatics play a crucial role in spatial data collection, land management,
and infrastructure development. One of the essential components in this field is horizontal
control, which serves as the foundation for accurate positioning and mapping. Horizontal
control extension and re-establishment are critical processes in ensuring the reliability and
continuity of geospatial data. This introduction provides an overview of these concepts, their
significance, methods, and applications in surveying and geo-informatics.
Horizontal Control in Surveying
Horizontal control refers to a network of precisely located reference points on the Earth's
surface, which serve as a framework for mapping and surveying activities. These points, known
as control points, provide a coordinate system that surveyors use to position other features
accurately. A well-established horizontal control network ensures spatial consistency and
accuracy in large-scale mapping projects, construction, and geospatial analysis (Ghilani &
Wolf, 2012).
Horizontal Control Extension
Horizontal control extension involves expanding an existing control network to cover new
areas where such points are sparse or nonexistent. This is necessary for the development of
new infrastructure, urban planning, and land subdivision. The process typically involves the
establishment of additional control points using various surveying techniques, including:
1. Traversing: A method that involves measuring angles and distances sequentially along
a predetermined path. It is commonly used in topographic surveys and construction
projects.
2. Triangulation: This technique utilizes a series of interconnected triangles to determine
positions over a large area. It was widely used before the advent of satellite-based
methods.
3. Trilateration: Instead of angles, this method relies on measuring distances to
determine the coordinates of new points.
4. Global Navigation Satellite Systems (GNSS): The use of GNSS, such as the Global
Positioning System (GPS), allows for rapid and precise determination of control points.
5. This modern method has significantly improved the efficiency and accuracy of
horizontal control extension (Leick, Rapoport, & Tatarnikov, 2015).
1
The extension of horizontal control networks ensures that all surveying activities are spatially
referenced to a common framework, reducing discrepancies and improving data integration
across different projects.
Horizontal Control Re-establishment
Over time, existing horizontal control points may be disturbed or destroyed due to natural
disasters, construction activities, or environmental changes. The re-establishment of these
control points is essential to maintain the integrity and continuity of spatial reference systems.
The process involves:
1. Reconnaissance and Data Recovery: Surveyors first identify and assess the damaged
or lost control points using historical data, maps, and field investigations.
2. Re-measurement and Adjustment: Using modern surveying instruments such as total
stations and GNSS receivers, surveyors re-measure the positions of control points. The
data collected is then processed using least-squares adjustment techniques to ensure
accuracy.
3. Monumentation: Durable markers, such as concrete monuments or metal rods, are
installed at the re-established control points to ensure their longevity and stability.
4. Verification and Documentation: The final step involves verifying the accuracy of
the re-established control points and documenting them for future reference (Ghilani &
Wolf, 2012).
Significance of Horizontal Control Extension and Re-establishment
The extension and re-establishment of horizontal control networks are fundamental for various
geospatial applications, including:

Land Surveying: Ensures accurate boundary delineation and land subdivision.

Infrastructure Development: Supports the construction of roads, bridges, and urban
development projects.

Geographical Information Systems (GIS): Provides accurate reference points for
spatial analysis and decision-making.

Disaster Management: Helps in post-disaster recovery by re-establishing control
points for reconstruction efforts.
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1.1 Statement of the problem
In many regions, the availability of reliable horizontal control networks is either limited or has
been compromised due to environmental changes, urban expansion, and infrastructure
development. The absence of a well-maintained control network leads to inconsistencies in
spatial data, inaccuracies in surveying activities, and increased costs in project implementation.
Additionally, natural disasters, human activities, and technological advancements necessitate
frequent updates and re-establishment of control points to maintain the integrity of geospatial
reference systems. The problem, therefore, lies in the need to systematically extend and reestablish horizontal control networks to support precise mapping, land administration, and
infrastructure planning. This research aims to address these challenges by exploring effective
methodologies for horizontal control extension and re-establishment, ensuring accuracy,
consistency, and efficiency in geospatial applications.
1.2
AIM AND OBJECTIVES
The aim of this study is to analyze and implement effective methodologies for the extension
and re-establishment of horizontal control networks to improve spatial accuracy, data
consistency, and efficiency in surveying and geo-informatics applications.
The specific objectives of this study are:
1. To examine the challenges associated with horizontal control extension and reestablishment.
2. To evaluate various traditional and modern surveying techniques used for horizontal
control network extension and re-establishment.
3. To develop a framework for improving the accuracy and reliability of horizontal control
networks.
4. To assess the impact of GNSS and other emerging technologies in enhancing horizontal
control network extension.
5. To propose best practices for maintaining and updating horizontal control networks to
ensure long-term reliability.
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1.3
Research Questions
1. What are the key challenges associated with the extension and re-establishment of
horizontal control networks?
2. How do traditional surveying methods compare to modern GNSS-based techniques in
horizontal control extension?
3. What are the impacts of environmental and human-induced factors on the stability and
accuracy of horizontal control networks?
4. How can the efficiency of horizontal control re-establishment be improved using
modern geospatial technologies?
5. What are the best practices for ensuring the long-term stability and maintenance of
horizontal control points?
1.4
Justification of the Study
The significance of horizontal control extension and re-establishment cannot be overstated, as
it pr
ovides the fundamental geospatial framework upon which accurate mapping, land
development, and infrastructure projects rely. The justification for this study is based on the
following reasons:
1. Improved Spatial Accuracy: A well-established and extended horizontal control
network enhances spatial accuracy, ensuring that geospatial data is reliable and
consistent across different applications.
2. Support for Infrastructure Development: Governments and private organizations
depend on accurate control networks for infrastructure projects, including road
construction, urban planning, and land parcel mapping.
3. Disaster Resilience and Recovery: In cases where natural disasters disrupt control
points, effective re-establishment strategies will facilitate post-disaster recovery
efforts by ensuring geospatial continuity.
4. Technological Advancement Integration: The study will assess the impact of
modern technologies such as GNSS, remote sensing, and GIS in optimizing horizontal
control extension and re-establishment.
5. Cost and Time Efficiency: By developing a systematic framework for control
extension, surveyors and geospatial professionals can reduce project costs and enhance
efficiency in data collection and analysis.
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1.5
1.6
List of Personnel
1. N/SG/23/3107 - AKINOLA HASSAN TAIWO
AUTHOR
2. N/SG/23/3104 - SANNI QUADRI AFOLABI
MEMBER
3. N/SG/23/3105 - ODUEKE JESUPELUMI JOHN
MEMBER
4. N/SG/23/3106 - TAIWO KEHINDE KING
MEMBER
5. N/SG/23/3108 - ANWOJURE OPEYEMI EMMANUEL
MEMBER
6. N/SG/23/3109 - SODIYA OLUSOLA OLAMIDE
MEMBER
7. N/SG/23/3110 - OGUNLEYE IREOLUWA AJIBOLA
MEMBER
8. N/SG/23/3111 - AJALA FATHIA BISOYE
MEMBER
9. N/SG/23/3112 - AKANJI RUKAYAT OLUWAKEMISOLA
MEMBER
10. N/SG/23/3113 - OGUNBAYO OLUWATOBILOBA FELIX
MEMBER
Study Area
The study will be conducted in Gbokoto Tuntun to Gbokoto Quarters, an area that has
experienced significant urban development and infrastructure expansion. This region has been
selected due to its growing demand for updated horizontal control networks to support
construction, land administration, and geospatial applications. The study area presents a mix
of urban and rural landscapes, providing a suitable environment for analyzing the challenges
and methodologies associated with horizontal control extension and re-establishment. Key
factors influencing this selection include accessibility, availability of previous control points,
and the need for improved geospatial accuracy in the region.
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CHAPTER TWO
2.0 LITERATURE REVIEW AND CONCEPTUAL FRAMEWORK
Horizontal control is a critical component of geodetic surveying, serving as the foundation for
spatial positioning and mapping. It consists of a network of precisely determined points that
are referenced to a common coordinate system, enabling accurate geospatial data collection.
The extension and re-establishment of horizontal control networks are necessary for various
applications, including cadastral mapping, infrastructure development, and geospatial
monitoring. Over time, control points may become outdated due to natural or human-induced
changes, necessitating their re-establishment or extension to ensure spatial accuracy.
Traditional surveying methods such as triangulation, trilateration, and traversing have
historically been used for horizontal control extension. These techniques rely on angular and
distance measurements using instruments like theodolites and total stations. While these
methods provide high accuracy, they require extensive fieldwork and clear intervisibility
between control points. With advancements in technology, the use of Global Navigation
Satellite Systems (GNSS), including Real-Time Kinematic (RTK) and Post-Processed
Kinematic (PPK) GPS, has significantly improved the efficiency and accuracy of horizontal
control networks. GNSS-based surveys allow for rapid data collection over large areas with
minimal field effort, reducing dependency on conventional methods. Additionally, remote
sensing and photogrammetry, particularly with high-resolution satellite imagery and
Unmanned Aerial Vehicles (UAVs), have emerged as effective tools for control network
extension, especially in inaccessible regions. Geographic Information Systems (GIS) further
enhance the management and analysis of control networks by integrating spatial data for
improved decision-making in land administration and development planning.
Despite technological advancements, several challenges hinder the effective extension and reestablishment of horizontal control networks. Differences in geodetic datums and coordinate
systems can introduce discrepancies, requiring rigorous transformation techniques to maintain
consistency. Environmental factors such as terrain variations, urban development, and land
subsidence can affect the stability of existing control points, necessitating periodic updates.
Additionally, the accuracy of control networks is influenced by instrumentation limitations,
atmospheric conditions, and human errors during data acquisition and processing. Addressing
these challenges requires a combination of robust geodetic principles, advanced surveying
techniques, and the integration of modern technologies.
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The relevance of horizontal control networks extends across multiple domains. In cadastral and
land administration, these networks provide a reference framework for property boundaries,
ensuring precise land ownership records. Infrastructure development relies on accurate control
points for road construction, railway alignments, and utility network planning. Furthermore,
horizontal control networks play a crucial role in disaster management by facilitating the
monitoring of land deformation and geohazard prediction. The evolution of surveying
methodologies continues to improve the efficiency and reliability of horizontal control
extension and re-establishment, ensuring the sustainability of geospatial data for diverse
applications.
CONCEPTUAL FRAMEWORK
The conceptual framework for horizontal control extension and re-establishment is built upon
the integration of geodetic principles, technological innovations, and environmental
considerations. At its core, geodetic principles govern the establishment and maintenance of
control networks, encompassing reference systems, coordinate transformations, and network
adjustments to minimize errors. The accuracy and reliability of horizontal control depend on
the selection of appropriate methodologies, whether through traditional surveying techniques,
GNSS-based positioning, or remote sensing applications.
Technological advancements play a pivotal role in shaping modern approaches to control
network extension. The adoption of GNSS technology has significantly improved precision,
reducing dependency on ground-based methods and enabling efficient data acquisition over
vast areas. The incorporation of remote sensing and UAV-based photogrammetry has further
enhanced data collection, particularly in regions where direct field measurements are
challenging. The integration of GIS provides a platform for analyzing and managing spatial
data, facilitating informed decision-making in geospatial projects.
Environmental and human factors also influence the stability and extension of horizontal
control networks. Natural elements such as terrain characteristics, climatic conditions, and land
deformation can impact control points, requiring regular assessments and updates. Urban
expansion, construction activities, and land-use changes may alter existing control networks,
necessitating their re-establishment to maintain spatial integrity. The effectiveness of control
extension depends on the ability to adapt to these dynamic influences while ensuring
consistency in geodetic positioning.
7
This framework illustrates the interplay between geodetic principles, technological
advancements, and environmental factors in the process of horizontal control extension and reestablishment. A systematic approach that incorporates precise measurement techniques,
modern surveying tools, and continuous monitoring is essential for sustaining reliable control
networks. By integrating these components, the framework supports the enhancement of spatial
data accuracy, ultimately contributing to the efficiency and sustainability of geospatial
applications.
2.1
Introduction of research focal point
The research on Horizontal Control Extension/Re-Establishment is centered on the need to
maintain and expand geodetic control networks to support accurate spatial positioning and
mapping. Horizontal control serves as the fundamental reference framework in surveying,
providing a system of precisely established points that enable consistent geospatial
measurements. Over time, existing control networks may become obsolete or compromised
due to natural phenomena such as land subsidence, erosion, and seismic activities, as well as
human-induced factors like urbanization and infrastructure development. As a result, the
extension and re-establishment of horizontal control points are crucial for ensuring the
reliability of geospatial data used in land administration, engineering surveys, and geographic
information systems (GIS).
This research focuses on the methodologies and technologies employed in extending and reestablishing horizontal control networks, considering both traditional and modern approaches.
Conventional techniques such as triangulation, trilateration, and traversing have been widely
used, but the advent of Global Navigation Satellite Systems (GNSS) and remote sensing
technologies has significantly enhanced the precision and efficiency of control extension. The
study aims to evaluate the effectiveness of various methods, examining their accuracy,
reliability, and practical applications in different environmental and infrastructural conditions.
Furthermore, the research investigates the challenges associated with maintaining an accurate
horizontal control network. Issues such as datum inconsistencies, environmental disturbances,
instrumentation limitations, and accessibility constraints affect the sustainability of control
networks. Addressing these challenges requires a combination of advanced geodetic principles,
technological innovations, and rigorous quality control measures.
By exploring the processes of horizontal control extension and re-establishment, this study
seeks to contribute to the improvement of geodetic practices in surveying and geo-informatics.
The findings will provide insights into best practices for maintaining control networks,
8
ensuring spatial accuracy in geospatial applications, and enhancing the efficiency of land and
infrastructure development projects. This research is essential in a rapidly evolving
technological landscape, where the demand for precise spatial data continues to grow across
various sectors.
2.2 Main Keywords Reviewed
In the context of Horizontal Control Extension/Re-Establishment, certain key terms are
fundamental to understanding the study. Two of the main keywords reviewed in this research
are Horizontal Control and Re-Establishment of Control Networks.
2.2.1 Horizontal Control
Horizontal control refers to a system of established survey points with precisely determined
coordinates (latitude and longitude or grid coordinates) that serve as a reference framework for
mapping, construction, and geospatial projects. These control points provide the foundational
spatial data required for accurate measurements, boundary demarcation, and engineering
works.
Importance of Horizontal Control

Geodetic Surveys: Horizontal control networks form the backbone of geodetic surveys,
ensuring consistency in large-scale mapping.

Infrastructure Development: Essential for road construction, pipeline alignment, and
urban planning.

Legal Boundaries: Used in cadastral surveys to define property lines and resolve land
disputes.

Disaster Management: Helps in monitoring ground movement, subsidence, and
tectonic shifts.
Methods of Establishing Horizontal Control
1. Triangulation: Traditional method using interconnected triangles to compute positions.
2. Trilateration: Measures
distances
between
Measurement (EDM) devices.
9
points
using
Electronic
Distance
3. Global Navigation Satellite Systems (GNSS): Utilizes GPS, GLONASS, or Galileo for
high-precision positioning.
4. Traversing: A series of connected lines with measured distances and angles.
Challenges in Horizontal Control

Environmental Factors: Weather, vegetation, and terrain can obstruct measurements.

Human Interference: Vandalism or construction may destroy control markers.

Technological Limitations: Requires high-precision instruments and skilled personnel.
2.2.2 Re-establishment of Control Network
Re-establishment refers to the process of recovering or re-surveying control points that have
been lost, damaged, or require verification due to changes in the landscape or advancements in
measurement technology.
Reasons for Re-establishment

Physical Destruction: Natural disasters, construction, or erosion may obliterate control
markers.

Technological Advancements: Older networks may need upgrading to align with
modern GNSS-based systems.

Legal Disputes: Re-surveying may be necessary to resolve boundary conflicts.

Urban Expansion: Rapid development may require denser control networks.
Steps in Re-establishing a Control Network
1. Historical Data Review: Examine previous survey records, maps, and coordinates.
2. Field Reconnaissance: Locate existing markers and assess their condition.
3. New Measurements: Use GNSS, total stations, or LiDAR to re-survey points.
4. Data Adjustment: Apply least-squares adjustment to ensure accuracy.
5. Monumentation: Install durable markers (e.g., brass disks, steel rods).
6. Documentation: Update geodetic databases and publish new coordinates.
10
Technologies Used in Re-establishment

GNSS (GPS/GNSS Receivers): Provides real-time kinematic (RTK) or post-processed
coordinates.

Total Stations: Combines angle and distance measurements for precise positioning.

LiDAR & UAV Surveys: Useful in inaccessible terrains for high-resolution data.
Challenges in Re-establishment

Cost & Resources: High-precision surveys require significant investment.

Data Consistency: Ensuring compatibility between old and new datasets.

Legal Compliance: Adhering to national geodetic standards.
2.3
Sub-topics under review

Geodetic Control Networks – Fundamental principles of control point establishment,
geodetic datums, coordinate systems, and transformation techniques.

Methods of Horizontal Control Extension – Traditional techniques such as
triangulation, trilateration, and traversing, along with modern methods like GNSS, RTK
GPS, and remote sensing.

Challenges in Horizontal Control Re-Establishment – Environmental disturbances,
human-induced changes, technological limitations, and geodetic datum inconsistencies.

Accuracy and Precision in Control Networks – Error minimization, network
adjustments, and quality control measures in geodetic surveying.

Applications of Horizontal Control Networks – Role of control networks in land
administration,
engineering
surveys,
disaster monitoring, and
infrastructure
development.
2.4
i.
Sub-Sub-Topics Under Review
Evolution of Geodetic Control Networks: Johnson (2018) examined the historical
advancements in geodetic control networks, highlighting their role in improving spatial
accuracy in surveying.
ii.
Impact of GNSS on Horizontal Control Extension: Smith and Allen (2020) explored
the integration of GNSS technology in horizontal control surveys, emphasizing its
contribution to precision and efficiency.
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iii.
Applications of Remote Sensing in Geodetic Control: Ayodele (2019) analyzed the
role of remote sensing in evaluating rock formations in Northern Nigeria, emphasizing
its relevance in geospatial studies.
iv.
Techniques for Accuracy Assessment in Control Network Re-Establishment:
Kim et al. (2021) discussed various methods for evaluating accuracy in geodetic
control networks, focusing on error minimization techniques.
v.
Challenges in Maintaining Horizontal Control Networks: Williams (2017)
investigated the factors affecting the stability of control points, including environmental
changes and human activities.
vi.
Role of UAV Photogrammetry in Geodetic Control Surveys: Li and Chen (2022)
examined the use of UAV photogrammetry in extending and re-establishing control
networks, emphasizing its efficiency in inaccessible areas.
vii.
Effects of Geodetic Datum Transformations on Control Networks: Garcia (2016)
explored the implications of datum shifts on control networks and outlined
methodologies for accurate coordinate transformations.
viii.
Integration of GIS in Horizontal Control Network Analysis: Patel and Singh (2018)
discussed the application of GIS in managing and analyzing control networks,
enhancing spatial data organization.
ix.
Urbanization and Its Impact on Control Network Sustainability: Thompson (2020)
studied the effects of rapid urban development on geodetic control networks,
emphasizing the need for periodic re-establishment.
x.
Application of Machine Learning in Surveying and Control Network
Optimization: Zhou et al. (2023) investigated the potential of machine learning
algorithms in improving the accuracy and efficiency of control network adjustments.
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CHAPTER THREE
3.0 MATERIALS AND METHODS
This chapter covers the materials and methods used in the horizontal control extension project,
with a focus on employing a digital theodolite as the primary instrument for establishing a
third-order control point network. Horizontal control extension is a crucial geodetic process
that expands existing reference points to support applications like topographic mapping,
cadastral surveying, and infrastructure development. The methodology takes advantage of the
digital theodolite’s precision and efficiency to achieve a horizontal accuracy of ±10–20 cm,
meeting third-order surveying standards.
3.1 INTRODUCTION
The methodology used in this study plays a key role in achieving the project’s main goal:
extending a horizontal control network. A well-structured and carefully executed approach
ensures that the collected spatial data is accurate, reliable, and consistent for various geospatial
applications. Since horizontal control serves as the foundation for most surveying and mapping
tasks, the procedures and tools must meet high precision standards. This chapter provides a
detailed breakdown of the materials—including hardware and software—as well as the stepby-step methods applied during the research.
3.2 MATERIALS
The materials used in this study include a selection of hardware and software tools chosen for
their reliability, compliance with geodetic standards, and ability to streamline fieldwork and
data processing under different environmental conditions.
3.2.1.1 HARDWARE
All survey equipment was checked for proper functionality and calibrated before measurements
were taken. Proper techniques and procedures were also considered. The following tools and
materials were used:
Digital Theodolite
Ranging Poles
Measuring Tape
Tripod Stand
Molding Wood
Cement
Sharp Sand and Gravel
Water
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Nail
Shovel
Head Pan
Cutlass
Field Book
Pen
Bucket
3.2.1.2 SOFTWARE
The following software programs were used for data processing and drafting:
AutoCAD 2007
Microsoft Excel
Microsoft Word
AutoCAD Civil 3D
3.3 METHOD
The methods in this study were designed to establish a third-order horizontal control network
through a systematic approach, combining traditional geodetic techniques with modern
technology. The workflow followed principles of consistency and redundancy to ensure
reliability, as supported by Okeke et al. (2018).
3.3.1 OUTLINE OF METHODS
3.3.1.1 Reconnaissance
Reconnaissance (often called recce in surveying) is the preliminary inspection of a site before
fieldwork begins. It helps surveyors assess the terrain, identify obstacles, plan equipment setup,
and determine the best survey methods. Reconnaissance can be conducted in two ways:
1. Office Reconnaissance
2. Field Reconnaissance
1. Office Reconnaissance
Office reconnaissance is the initial planning phase, where preliminary data is gathered to
determine personnel needs, equipment requirements, and time estimates before fieldwork
begins.
. Planning Stage
This stage involves thorough preparation, including analyzing project specifications,
14
selecting appropriate instruments, testing equipment for accuracy, and choosing the best
survey methodology. Sections 3.3.1.1a and 3.3.1.1b below provide the exact coordinates of
the starting and closing control points for the survey.
Table 3.3.1: Coordinates of starting controls used.
STATION
NORTHING(m)
EASTING(m)
HEIGHT(m)
HND1 2023/27
761848.081
498174.838
76.957
HND1 2023/26
761730.444
498172.438
76.911
HND1 2023/30
761724.278
498159.435
76.657
2. Field Reconnaissance
Field reconnaissance is the process of an extent study of an entire area that might be used for
needed logistics and where the control points will be located, point of commencement and point
of termination, the accuracy required for the control, and which survey instruments will be
required for the project the recce diagram for the entire area was drawn not to scale and it’s as
shown below.
Table 3.2 Horizontal Collimation Error Test
STATION
A
SIGHT
FACE
HORIZONTAL
VERTICAL
C.R
C.R
B
L1
48°55’30”
C
L2
231°24’22”
90°55’11”
C
R2
51°24’47”
269°05’01”
B
R1
228°55’15’
HORIZONTAL COLLIMATION ERROR
Horizontal collimation error is done in this project to check error in horizontal circles readings.
R1 – L1 = 288°55’15” - 48°55’30” = 179°59’45”
L1 – R2 = 231°24’22” - 51°24’47” = 170°59’35”
Differences = 00°00’10”
L2 – L1 = 231°24’22” - 48°55’30” = 182°28’52”
R2 – R1 = 51°24’47” - 228°55’15” = 182°28’42”
Differences = 00°00’10”
Horizontal collimation error = 00°00’10”
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VERTICAL COLLIMATION ERROR
Vertical collimation error is done in this project to check error in vertical circle readings
V1 - 90°00’00’= 90°55’11” - 90°00’00” = 00°55’11”
270°00’00” – V2 = 270°00’00” - 269°05’01” = 00°54’59”
Difference = 00°00’12”
These trusted reference points, surveyors can confidently that their work meets the stringent
accuracy requirements of engineering, legal, or scientific project. Below is a more detailed and
comprehensive explanation of the control check process and its significance in surveying.
3.4 Control Check
A control check was conducted to verify the stability and reliability of the established control
points. This process ensured that the controls had not been tampered with, disturbed, or
shifted from their original positions.
The procedure involved setting the instrument on control pillar HND1 2023/27 and taking a
backsight observation on both face left and face right to control pillar HND1 2023/30. A
foresight observation was then taken on face left to control pillar HND1 2023/27. The
instrument was subsequently transited to face right, and another observation was taken to
control pillar HND1 2023/30. All observations were carefully recorded for accuracy
assessment.
Table 3.3. Angular observation in control point
STATION SIGHT
FACE
H. C. R
REDUCED MEAN
H. C. R
HND1
V. C. R
H. C. R
L1
52°33’23”
L2
296°07’36” 243°34’13”
89°01’09”
R2
116°07’48” 243°34’17”
243°34’15” 271°04’08”
R1
232°33’31”
2023/27
HND 1
HND1
2023/26
2023/30
HND1
2023/30
HND1
2023/27
Table 3.4. Back computation of starting control
BEARING DISTANCE ΔN
ΔE
16
NORTHING
EASTING
STATION
761848.081
498174.838
HND1 2023/27
01°10’08”
117.661
-117.637 -2.400
761730.444
498172.438
HND1 2023/26
64°44’16”
14.390
-6.166
761724.278
498159.435
HND1 2023/30
-13.003
From table 3.4 and 3.5 above
The back bearing from HND1 2023/26 to HND1 2023/27 = 01°10’01” + 180°
= 181°10’08”
Forward bearing from HND1 2023/26 to HND1 2023/30 = 64°44’16”
Included angle = back bearing – forward bearing
= 64°44’16” - 181°10’08”
= -116°25’52” + 360°
= 243°34’08”
Computed angle from the field observation = 243°34’15”
Discrepancy = 243°32’15” - 243°34’08”
= 00°00’07”
Angular accuracy = 30” √n, where n is 3
= 30”√3
= 00°00’52”
Table 3.5 Linear check observation of the controls used
FROM
COMPUTED
MEASURED
DIFFERENCES TO STATION
STATION
DISTANCE
DISTANCE
(m)
(m)
(m)
HND1 2023/27
117.661
117.670
0.009
HND1 2023/26
HND1 2023/26
14.390
14.397
0.007
HND1 2023/30
3.5 Field Operations and Procedure
This stage involves the application of methods, tasks, and principles adopted in the field to
collect data necessary for producing both the cross-section and profile plan of the road. The
following procedures were carried out to achieve the project objectives.
3.6 Theodolite Traversing
Theodolite traversing was performed through four basic steps: setting, centering, leveling,
and focusing. The procedure adopted is outlined below:
1. The tripod legs were equally spaced, and the tripod head was set approximately level.
2. The tripod was positioned so that the head was directly over the survey point.
17
3. The theodolite was mounted on the tripod using a tribrach and clamped securely.
4. The instrument was fixed in place with the centering screw while being braced with the
other hand.
5. The optical plummet was focused directly on the survey point.
6. The leveling foot screws were adjusted until the survey point was centered in the optical
plummet reticle.
7. The bubble was centered in the circular level by adjusting the tripod legs.
8. The horizontal clamp was loosened, and the instrument was rotated until the plate level
became parallel to two leveling screws.
9. The bubble was centered using the leveling screws by turning them clockwise. The
instrument was then rotated 90° and leveled again using the third leveling screw.
10. After re-tightening the centering screw, the plate level bubble was checked to ensure
proper leveling in multiple directions.
3.7 Detailing
Detailing was carried out to establish the alignment of the road and determine its shape,
length, and direction. During this process, existing structures such as buildings, electric poles,
and culverts were fixed.
Successive points determined in both the main and subsidiary traverse served as base stations
for fixing all existing features along the route. Traverse rays and chain survey methods were
effectively combined to capture these details.
The instrument and target were set up on control points, with necessary temporary adjustments
made. Observations were first taken to the back target and recorded, followed by forward
observations made with the aid of a ranging pole mounted on control points marked
numerically on the reconnaissance diagram. Each feature observed was serially numbered and
recorded in the field book. The target was then moved to subsequent points until all features
along the route were observed. The instrument was later shifted to the next station to repeat the
process.
3.8 Plotting of Traverse Lines
The traverse lines were plotted using the corrected coordinates obtained from traverse
computations.
3.8.1 Plotting of Profile
The profile was plotted to represent both the existing ground level along the centerline and
the proposed formation level. Perpendicular lines were drawn at every horizontal chainage
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(25 m intervals). The differences in height between the reduced level and datum were scaled
along these lines, after which the points were joined to form the profile.
3.8.2 Plotting of Details
All existing details such as roads, buildings, drainages, and electric poles were plotted with
reference to the main traverse line along the road’s centerline.
3.9 Recce Diagram
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