All Flashcards
d (212 cards)
1
Q
What is the Geoid
A
The geoid is an equipotential surface that corresponds with the mean sea level to take into account the mountainous or flatter land areas to estimate the shape of the earth.
2
Q
What is the Ellipsoid
A
The ellipsoid is a mathematical shape that describes the earth’s surface as a best fit, however doesn’t take the topography of the earth into account.
3
Q
Map projections used by OS for the UK
A
The map projections used by the ordnance survey (OS) is a modified transverse Mercator projection.
4
Q
OSGB36
A
The OSGB36 is a datum used by ordnance survey based on a transverse Mercator projection of Airy’s ellipsoid.
5
Q
OSTN15
A
OSTN15 is a transformation model used to convert between OSGB36 the UK national coordinate system and ETRS89 a European coordinate system.
6
Q
OSGM15
A
OSGM15 is a transformation model used to convert geodetic heights (ellipsoid) to orthometric heights (mean sea level).
7
Q
Types of heights
A
Three different heights are ellipsoidal height, orthometric height and geoidal height; the most commonly used is the orthometric height.
8
Q
GNSS
A
GNSS stands for global navigation satellite system.
9
Q
Reference system for GNSS positions
A
GNSS positions are usually expressed in the WGS84 (world geodetic system 1984).
10
Q
European satellite system
A
The name of the European satellite system is Galileo.
11
Q
National Mapping Agency for the UK
A
The National Mapping Agency for the UK is the ordnance survey (OS).
12
Q
RINEX file
A
A RINEX (receiver independent exchange format) file is a format for raw satellite navigation system data from GNSS and can be found from sources such as international GNSS service (IGS).
13
Q
Network RTK
A
A RTK (real time kinematic) VRS (virtual reference station) network is a system of reference stations that are used to provide real-time corrections to GPS data to enhance accuracy and efficiency.
14
Q
Fundamental positioning process in GNSS
A
The fundamental positioning process used in GNSS coordinate determination is trilateration.
15
Q
Mitigating ionospheric error in GNSS
A
To mitigate ionospheric errors in GNSS positioning, techniques like dual-frequency receivers, Precise Point Positioning (PPP), and Real-Time Kinematic (RTK) can be employed.
16
Q
Autonomous GNSS positioning
A
Autonomous or standalone GNSS operation uses radio signals from GNSS satellites alone. No other sources of augmentation or correction are used in the position computation.
17
Q
Geoidal separation
A
Geoidal separation, also known as geoid undulation, is the vertical distance between the geoid (mean sea level) and the reference ellipsoid used in GNSS systems, such as WGS84.
18
Q
Site calibration or localization
A
Site calibration, also known as localisation, is a process used in surveying and GPS/GNSS projects to align or transform GPS data with a local, project-specific coordinate system.
19
Q
UK national height datum origin
A
The UK national height datum was originally based in Newlyn, Cornwall.
20
Q
UK National Grid map projection
A
The UK National Grid is based on a Modified Transverse Mercator projection.
21
Q
Minimum satellites for GNSS position
A
A minimum of four satellites are needed in order to establish a GNSS position.
22
Q
Segments of GNSS
A
GNSS is comprised of three segments: the space segment, the control segment, and the user segment.
23
Q
Distance measurement in GNSS
A
Distances (ranges) are measured by measuring the time it takes for a signal to travel from a satellite to the receiver.
24
Q
Integer Ambiguity
A
The Integer Ambiguity is the unknown number of full wavelengths present in the phase measurement between a satellite and a receiver.
25
Sources of error in GNSS measurements
Sources of error in GNSS measurements include atmospheric delays, satellite clock and orbit errors, multipath interference, and receiver noise.
26
Ways to describe a position
Three different ways to describe a position are coordinate system, relative, and absolute position.
27
Surveying measurements
Includes horizontal angles, vertical angles, and distances (horizontal, slope, vertical).
28
Scales
Ratio between the drawing of an object and the actual object, expressed in words, drawn scale, or fraction (e.g. 1cm represents 2m, 1:200).
29
Azimuth
A horizontal angle that always measures clockwise from North, used to indicate a direction.
30
Bearing
Angular measurement with a range of 0° ≤ Bearing < 90°.
31
Quadrant I Azimuth
Azimuth = theta.
32
Quadrant II Azimuth
Azimuth = 180° - theta.
33
Quadrant III Azimuth
Azimuth = 180° + theta.
34
Quadrant IV Azimuth
Azimuth = 360° - theta.
35
Trilateration
The determination of a point's position using measured distances to that point from at least three known points.
36
Triangulation
The determination of a point's position using measured angles from at least two other known points.
37
Temperature Correction
Correction applied to tape measurements due to temperature differences, calculated as Correction = α * L * (t - ts).
38
Coefficient of Linear Expansion (α)
A constant that represents how much a material expands per degree of temperature increase.
39
Surveying
The process of measuring distances, angles, and positions to determine the location of points on the earth's surface.
40
What are the three types of errors in surveying measurements?
gross errors, systematic errors, random errors
41
What are gross errors and how can they be minimized?
high or low values compared to other measurements mainly due to observer inexperience. They can be minimized by repeating measurements.
42
What characterizes systematic errors in surveying?
always have the same magnitude and sign, resulting in a bias from the true value
43
How can systematic errors be minimized?
By maintaining and calibrating instruments properly and following correct measurement procedures.
44
What defines random errors in measurements?
Random errors vary in sign and magnitude, are unavoidable
45
What is accuracy in the context of measurements?
Accuracy is a measure of reliability defined as the difference between the true value and the most probable value (MPV).
46
How is the most probable value (MPV) determined?
MPV is usually the arithmetic mean of a set of observations.
47
What is the probable error (residual) in measurements?
The difference between the MPV and each observation.
48
What is the true error in measurements?
The difference between the true value of a quantity and the value obtained by an observation.
49
What is the relationship between accuracy and errors?
Accuracy is affected by systematic and gross errors and it is not known but can be estimated from residuals.
50
How is precision defined in surveying?
Precision is a measure of repeatability and can be numerically defined.
51
What is the difference between precision and accuracy?
Precision refers to the repeatability of measurements, while accuracy refers to how close a measurement is to the true value.
52
What does a high precision indicate about probable errors?
indicates small probable errors (residuals).
53
What is the significance of the standard deviation in measurements?
indicates the amount of variation about a central value and reflects uncertainty in the measuring process.
54
What are outliers in a data set?
values that are very different from the rest of the values in a set of repeated observations, often outside ±3σ.
55
What is the standard error (SE) in measurements?
a measure of the precision of the mean of a sample describing average observation errors.
56
How does the number of observations affect the standard error?
The standard error decreases as the number of observations increases.
57
What is the law of error propagation in surveying?
errors in measurements result in errors in calculated values and these errors can be propagated from measurements to calculated values.
58
What does a tall thin curve in a normal distribution indicate?
It indicates high precision with small scatter of measurements.
59
What does a flatter curve in a normal distribution indicate?
It indicates low precision with larger random errors.
60
What is the significance of the arithmetic mean in a normal distribution?
the central value around which the distribution of measurements is symmetrical.
61
What is levelling in land surveying?
Levelling is the procedure used for determining or comparing the difference in heights between points on the earth's surface.
62
What is another name for the levelling process?
Transferring Heights
63
How are heights typically given in levelling?
Heights are normally given relative to a plane or datum.
64
What is the UK datum for heights?
The datum for heights in the UK is defined at mean sea level in Newlyn, Cornwall.
65
What are elevations in the context of levelling?
Heights relative to the UK datum are referred to as elevations.
66
What equipment is needed for a levelling survey?
A level and a levelling staff.
67
What does a level do in levelling surveys?
A level is a device that provides a truly horizontal line.
68
What is the purpose of a levelling staff?
A levelling staff is used for reading vertical heights.
69
What is the length of a typical levelling staff?
A typical levelling staff is 5 meters long when extended.
70
What is the first step in setting up a level?
Set up the tripod with the levelling head approximately level and securely attach the instrument.
71
How do you center the small bulls eye bubble when setting up a level?
Use the three foot screws to center the bulls eye bubble.
72
What is the Line of Collimation?
the imaginary line that passes through the crosshair of the eyepiece and the optical center of the objective.
73
What is parallax in the context of levelling?
Parallax is the displacement or difference in the apparent position of an object viewed along two different lines of sight.
74
What is a Change Point in levelling?
A Change Point is where two readings are taken on the staff: a foresight (F/S) followed by a backsight (B/S) after moving the level.
75
What should be ensured about a Change Point?
It should be on a hard surface that does not allow the staff to move vertically between readings.
76
What is the procedure when the distance between benchmark and point is greater than 50 m?
Set up the instrument, take a backsight at a known point, move the levelling staff, and take intermediate sights if required.
77
What is the purpose of the two-peg test?
The two-peg test checks whether the line of collimation of a level is horizontal or if it needs adjustment.
78
What are gross errors in levelling surveys?
Gross errors include user errors such as wrong readings, wrong bookings, and not taking two readings at a Change Point.
79
What are systematic errors in levelling surveys?
Systematic errors arise from improper levelling of the instrument, malfunction, parallax, or incorrect staff extension.
80
What are random errors in levelling surveys?
Random errors can be caused by factors like wind, incorrect reading of bookings, or vertical movement of the staff.
81
How often should the two-peg test be carried out?
The two-peg test should be carried out regularly, e.g., once per week or two, depending on the frequency of level use.
82
What are the acceptable error limits for levelling according to Uren and Price?
1 mm per 20 m.
83
What are the acceptable error limits for levelling according to Wimpey?
4 mm per 50 m.
84
What are the two fundamental types of angles in surveying?
Horizontal and vertical angles.
85
What is the use of vertical angles in surveying?
To determine the elevation of points and distances.
86
What is the purpose of horizontal angles in surveying?
To obtain direction and set out points.
87
What is the first step in setting up a total station?
Position the tripod over the survey station as level and well-centred as possible.
88
What is the purpose of the laser plummet in setting up a total station?
To centre the instrument exactly on the survey point.
89
How is the instrument levelled after being approximately centred?
By using the tripod legs and footscrews.
90
What is a double-face observation in measuring horizontal angles?
It involves taking readings from both face left (FL) and face right (FR) positions to minimise systematic errors.
91
What should the readings from sighting at a target on Face Left and Face Right differ by for horizontal angles?
180 degrees.
92
What should the readings from sighting at a target on Face Left and Face Right sum to for vertical angles?
360 degrees.
93
What are the three types of errors in angle measurements?
Gross errors, random errors, and systematic errors.
94
How can gross and random errors be minimised in angle measurements?
By taking repeated measurements.
95
What is the general acceptance criterion for levelling between benchmarks? ±5mm.
96
What are the two methods of setting out a point position? 1. Setting out from reference line and offsets. 2. Setting out from polar coordinates using an angle from a reference bearing and a distance from a reference point.
97
What are the steps for setting out using polar coordinates? 1. Set up total station at Point 1 and sight at Point 2.
98
2. Measure distances xA and xB along line 1-2.
99
3. Set up at A'
sight at Point 1
100
What are sight rails? Horizontal timbers that define the plane of the finished works at a level above the ground.
101
What is a traveller in the context of vertical control? A portable sight rail with a vertical support
used to check excavation depth.
102
What is the process for setting out gradients using sight rails? The same process as setting out along a horizontal plane
but the sight rails are called batter rails.
103
What is the purpose of batter rails? They are used for setting out slopes or drainage.
104
What is a laser level and its function in large earthwork projects? A laser level is fixed to a tripod
levelled
105
What is chainage in road construction? Chainage indicates distance along the road measured from the starting point of the scheme.
106
What are the basic parts of a circular horizontal curve in road design? Two straights meet at the point of intersection I
with a circular arc running between them
107
What is the deflection angle in the context of circular curves? The angle θ between the tangents at the points of intersection.
108
What is the significance of accurate positions in machine control for road curves? Accurate positions ensure that the curves are set out correctly according to the design model.
109
What is the role of a total station in setting out procedures? It is used to measure distances and angles for accurate positioning of points on the ground.
110
What is the importance of knowing the coordinates of set up stations in field procedures? They are essential for accurate measurements and setting out of the project.
111
What is the EDM function of a total station used for? It is used to measure distances accurately during the setting out process.
112
What should be done before using a traveller for excavation checks? Both profiles should be in place to ensure accurate depth measurements.
113
What is the purpose of profile boards in road construction? They indicate the finished level of the road and help guide excavation.
114
How is the height of sight rails determined? It is set to give the correct excavation depth based on the required finished level.
115
What is the purpose of a traverse in surveying?
To determine positions and areas.
116
What are the four types of traverses?
Open loop traverse and closed loop traverse.
117
open line traverse and closed line traverse
118
What distinguishes a closed loop traverse from an open loop traverse?
A closed loop traverse has enough measurements to calculate positions and errors, while an open loop traverse has just enough measurements to calculate positions only.
119
What is a loop traverse?
A loop traverse starts and returns to the same location.
120
What is a line traverse?
A line traverse has different starting and ending points.
121
What are traverse lines?
The lines joining the survey stations.
122
What is required for surveying a large area?
A network of survey stations.
123
What is the method for calculating angles in traverse surveying?
Average angles from field measurements (FL and FR) in different rounds.
124
What is the basic geodetic problem in traverse surveying?
Calculation of coordinates.
125
What types of errors are considered in traverse measurements?
Spatial error from traverse line measurements and angular error/misclosure from internal angles.
126
What is the first step in determining the coordinates of each station in a traverse?
Knowing the coordinates of one station.
127
What is the role of traverse line measurements in error determination?
They help assess spatial errors in the survey.
128
What is the outcome of having enough measurements in a closed traverse?
It allows for the calculation of positions and errors.
129
What is the general approach to measuring angles in the field for a traverse?
Using precise instruments to measure the internal angles and lengths of traverse lines.
130
What information is needed to determine the azimuth of a traverse line?
The coordinates of a station associated with the traverse and the azimuth of a line to one of the traverse stations.
131
How do you calculate the azimuth of a traverse line starting at a station?
Add the internal clockwise angle at that station to the azimuth of the previous line.
132
What is the formula for calculating closing error in spatial coordinates?
Error(x) = Calculated x (Easting) coordinate of the last station - known x (Easting) coordinate of the last station.
133
How is the total traverse error calculated?
Total traverse error = √(∆x² + ∆y²).
134
What is the formula for precision of the traverse?
Precision of the traverse = Total error / total traverse length.
135
What is the purpose of adjusting spatial errors in a traverse?
To ensure the calculated coordinates match known coordinates, improving accuracy.
136
What is the difference between angular error adjustment and spatial error adjustment?
Angular error adjustment distributes error evenly across angles, while spatial error adjustment accounts for line lengths.
137
What is the role of the azimuth in traverse calculations?
The azimuth indicates the direction of a traverse line relative to a reference direction.
138
What is the importance of knowing the azimuth of a traverse line?
It is essential for accurately determining the direction and position of traverse lines.
139
What are the two types of angles that can be checked in a closed loop traverse?
Internal angles and external angles.
140
How do you calculate the angular error in a closed line traverse?
By calculating the azimuths of the traverse lines and comparing the last azimuth obtained with the given/known one.
141
What method is used to adjust angles/azimuths in a traverse?
Use the adjusted angles to calculate the azimuths for the relevant columns.
142
What is the Bowditch method used for in surveying?
It is used for adjusting errors in a closed loop traverse by distributing the error proportionally based on line lengths.
143
What is the adjustment formula for E in the Bowditch method?
uΔx = (line length / total length) * errorx
144
In a closed line traverse, what should the sum of adjustments for E be?
Sum[7] should equal 0; if not, divide the difference accordingly.
145
In a closed line traverse, what should the sum of adjustments for N be?
Sum[8] should equal 0; if not, divide the difference accordingly.
146
What should the last entry for E equal in a closed line traverse?
The last entry [5] should equal the first entry [5] plus sum[7].
147
What should the last entry for N equal in a closed line traverse?
The last entry [6] should equal the first entry [6] plus sum[8].
148
What is the purpose of calculating azimuths in a traverse?
To determine the direction of the traverse lines and adjust for any angular errors.
149
What is an essential step before adjusting azimuths in a closed traverse?
Calculate the azimuths of the traverse lines.
150
What is the expected outcome of a well-conducted closed line traverse?
The start and end points should coincide, indicating no significant errors.
151
Contour
A contour is a line that joins all points of the same height relative to a datum.
152
Elevation
The height of a point relative to the Mean Sea Level (MSL).
153
Contour Interval
The height difference between successive contours, which is constant on a topographic map.
154
Constant Distance Between Contour Lines
Indicates constant gradient of the ground.
155
Main Use of Contour Plans
To create vertical sections.
156
Coordinates for area calculation
If the coordinates of the points are known then the enclosed area is calculated as the sum of the trapezoid areas formed by the points and their projections on the y- or the x-axis moving CLOCKWISE.
157
Chainage interval
The strip width used in volume calculations.
158
Level section
A cross-section that is flat and does not have a gradient.
159
Partial embankment
A combination of cut and fill.
160
What are the different ways to describe a position?
Coordinate system, relative position, and absolute position.
161
What is relative position used for?
Setting out and monitoring displacements of a structure, usually for small areas that can be assumed as a plane.
162
What must be considered for large project areas when describing position?
The shape of the Earth.
163
What is the Geoid?
An equipotential surface that best fits Mean Sea Level (MSL) and is defined by gravity.
164
How does gravity affect the shape of the Earth?
Gravity varies, defining the shape of the Earth and creating multiple closed level surfaces of different potential energy.
165
What is the reference datum for terrestrial measurements?
Mean Sea Level (MSL).
166
How does the Geoid differ between countries?
Local geoids can be parallel to the Geoid but offset, such as in mainland UK where it is 80cm below the Geoid.
167
What is EGM96?
The Earth Gravitational Model 1996, which is the most precise global geoid.
168
What is the shape of the Earth described by the ellipsoid?
A mathematical shape, an ellipse of rotation around its semi-minor axis.
169
What are the best-fitting global ellipsoids?
GRS80 (Geodetic Reference System 1980) and WGS84 (World Geodetic System 1984), which is based on GRS80.
170
How does the Geoid relate to the Reference Ellipsoid?
The Geoid does not coincide with the Reference Ellipsoid and can differ by up to 100m in some places.
171
What is the local ellipsoid used in Great Britain?
Airy (1830).
172
What is the geographic coordinate system used for?
To define a position on an ellipsoid, requiring knowledge of the specific ellipsoid.
173
What are the angles measured in the geographic coordinate system?
Longitude (East-West) and Latitude (North-South).
174
What is ellipsoidal height?
The distance of the Earth's surface above or below the ellipsoid.
175
What is orthometric height?
Geoid height used in most engineering surveys.
176
What is the significance of the Geoid model in height conversion?
Different Geoid models can result in different orthometric heights for the same ellipsoidal height.
177
What is the datum in the context of positioning?
A set of parameters that define the coordinate system and its position relative to the Earth's surface.
178
What is a datum realization?
Known points that make the coordinate system accessible to users, such as OSGB36.
179
What is the purpose of map projections?
To compute map coordinates from latitude and longitude of an ellipsoid, minimizing distortion.
180
What are the three main types of surfaces used for map projections?
Cylindrical, conical, and azimuthal (planar).
181
What is projection distortion?
The unavoidable distortion that occurs when a curved surface is flattened.
182
What is a conformal projection?
A projection where the ratio between two lengths is preserved, making it favorable for engineering applications.
183
What is the Transverse Mercator projection?
A conformal projection ideal for countries with a north-south extent, where the central meridian is at 90 degrees to the equator.
184
What is the OS National Grid?
The national mapping agency for Great Britain, based on a transverse Mercator projection of Airy's ellipsoid.
185
What is the scale factor in mapping?
A number that converts grid distances to ground distances and vice-versa.
186
What are the implications of scale error in mapping?
It refers to the difference between the distance on the ground and the projected distance.
187
What is deformation monitoring in civil engineering? Regular measurements of changes in the shape or dimensions of infrastructure due to applied loads
aimed at ensuring structural integrity.
188
What types of deformations are measured in deformation monitoring? Vertical changes (settlements)
horizontal changes (dam crest and bridge deck deflections)
189
What are the primary reasons for monitoring deformations in civil infrastructure? For research (understanding processes
development and testing of new materials) and for safety (detecting faults early
190
What are some causes of structural deformation? Ground movements (landslides
ground uplift)
191
What instruments are commonly used for deformation monitoring? Total stations
tiltmeters
192
What factors affect the choice of monitoring technology? Required precision
real-time requirements
193
What should be considered when designing a monitoring system's geometry? Expected movements/deformations
which part of the structure to monitor
194
What is the goal of data analysis in deformation monitoring? To obtain a set of displacement values for discrete points on a structure relative to stable reference stations.
195
What are the basic analysis steps for deformation monitoring data? 1. Understand your data through various plots; 2. Determine significance vs. instrument noise; 3. Define time trends; 4. Check for seasonal behavior; 5. Physically interpret correlations or causative relationships.
196
What is the significance of plotting monitoring data over time? It allows for identification of points with maximum and minimum displacements and understanding if deformation is uniform across the structure.
197
What is curve fitting in the context of deformation monitoring? A method used to minimize differences between observed and estimated values for all measurement points
often using the Least Squares approach.
198
What is the Fast Fourier Transform (FFT) used for in deformation monitoring? To transform a time series from the time domain to the frequency domain
assuming any signal is a sum of signals of different frequencies.
199
What is the importance of detrending data in deformation monitoring? It allows for the identification of patterns
such as seasonal effects
200
What is the role of correlations in physical interpretation of deformation data? To analyze relationships between observations in the time domain or frequency domain
helping to understand influences on deformation.
201
What are some examples of monitoring system configurations? Monitoring of an arch dam
landslide monitoring
202
What is the purpose of monitoring deflections in a composite rail bridge? To assess the effects of passing train loads on the bridge's structural integrity.
203
What is the significance of understanding the expected magnitude of movements/deformations? It helps in designing appropriate monitoring systems and selecting suitable instrumentation.
204
What is the role of environmental factors in deformation monitoring? They can significantly affect the stability and behavior of structures
necessitating their consideration in monitoring plans.
205
What is the significance of using multiple methods for data analysis in deformation monitoring? It provides a comprehensive understanding of the data
allowing for better identification of trends and anomalies.
206
What is the relationship between data analysis and structural integrity? Data analysis provides insights into the current condition of the structure and helps predict future behavior
ensuring safety.
207
What is the importance of monitoring technology accessibility? It affects the feasibility of implementing and maintaining monitoring systems in various environments.
208
How does seasonal behavior affect deformation monitoring data? Seasonal variations can influence the readings
making it essential to account for these patterns in analysis.
209
What is the impact of outliers on the Least Squares approach in data analysis? Outliers can significantly affect the results
necessitating caution in using this method for curve fitting.
210
What is the significance of identifying significant trends in deformation data? It helps in understanding how deformations evolve over time
which is crucial for maintenance and safety planning.
211
What is the role of reference stations in deformation monitoring? They provide stable points against which displacements of monitored points are measured.
212
What is the purpose of using remote sensing technologies in deformation monitoring? To gather data on structural changes over large areas or inaccessible locations.
