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Control• To start any surveying project, surveyors need to
start measurements from known points: points of
known coordinates.
• In the vertical, one benchmark is enough.
• In the horizontal (X, and Y) you need at least two
points
• onsite of known presicse elevation, we call it a
benchmark.
Vertical control
Elevations• For any elevation measurements onsite:
• a backsight is recorded at the benchmark;
• the height of instrument si computed: HI =
EBM + BS
• The elevation of any point = EBM – (FS or IS)
• Therefore, you have to have at least one point.
• A set of benchmarks ar established around the
site before any construction design or activity
by measurements from government provided
benchmarks
Horizontal Control
• To measure (X, Y) horizontal coordinates, you need to
occupy one know point say (A), aim at another known
point, say (B). The unknown point is C
• Calculate the azimuth of the line AB = tan-1 X/ Y
• Measure the angle BAC and the distance L to the
unknown point C
• Calculate the azimuth of the line AC
= Azimuth of AB ± angle BAC
Calculate X and Y for the line AC
Calculate the coordinates of C:
Xc = XA + X and Yc = YA + Y
Example 1
Calculate the azimuth of AB if the azimuth of
AB = 40 and the angle BAC = 25
Answer:
= 65
N
40 C25
AZ AC
A
B
Given that the coordinates
of point A (543.12,
341.67)m. The azimuth of
the line AB in the figure
below = 65 (that is 65
degrees) and the
horizontal length between
points (A) and (B) is
145.23 m. Calculate the
coordinates of point (B).
6
Coordinate Computations
Example 2
Answer:
XAB
= L sin() = 145.23 sin (65) = 131.62 m
YAB
= L cos() = 145.23 sin (65) = 61.38 m
Then;X
B= X
A+ X
AB= 543.12 + 131.62 = 674.74
YB
= YA
+ YAB
= 341.67 + 61.38 = 403.05 m
Coordinate ComputationsExample 2
• Therefor, you need at least two known points
to calculate a reference azimuth, such as the
azimuth of AB in the previous example.
• Note that we do not measure azimuth as it is
very difficult to figure out where north is, but
we need the azimuth to compute coordinates.
• We solve the problem by measuring angles
between lines, compute the azimuth of one of
them, and then use the measured angle to
compute the needed azimuth.
Horizontal Control
Summary• In summary, we need to have points of precise
coordinates around the site to measure from.
• For elevations, the vertical, we establish
“benchmarks” by measurements of elevations from
government provided benchmarks.
• For X and Y, horizontal coordinates, we establish
horizontal control points by:
• Measurements from other known points; or
• Using GPS (explained later in this course)
Stages and Measurements of CS
• Design stages: topographic Surveying, and site maps
• Construction stage:
• Setting-out and positioning works. 60% of surveying hours.
• involves establishing lines and grades by means of stakes and string lines to guide the contractor
• During and after construction: as built drawings, a record and a check.
• Measurements involved: Horizontal and vertical angles, elevations, horizontal distances.
CS Equipment• Laser Instruments:
– to create a visible line, or plane of known elevation or tilt
– The line or plane could be horizontal, vertical, or tilted.
– Single beam lasers will project visible string lines or plumb lines
– Rotating beam lasers: a rotating single beam to create a plane.
– Examples:
» Laser levels, laser theodolite and total stations, hand-held EDM instruments (Figures 23-1 to 23-4)
» Recent technology of prism-less total stations and EDMs.
» Machine Guidance
•Total Stations: the ones designed for CS are of lower angular resolution(10” or 20”), and shorter ranges(500 m)
•Relative GPS: sub-centimeter accuracy with real time kinematic GPS in horizontal, few cm in vertical. Must maintain visibility with satellites
•Levels
Staking out a Building
• First step is to locate the building by boundary surveying. Stakes are placed temporarily at the corners as a check.
• In a small size building, a set of batter boards and reference stakes are first set. The boards are around the building corners and nailed at a certain elevation above the footing base or at first floor elevation.
• Nails are driven into the batter board tops so that a string connecting them will define an outside wall
• In a larger building, radial methods are used using a total station
Batter Boards هالخنزير؟ماهى الخنزيرة أو الشبلونة
ربع هى هيكل خشبى مؤقت يتم اعداده على شكل م:تعريف الخنزيرة
أو مستطيل أو طبقا لشكل المبنى على الأرض المطلوب أقامة
.زيرةالمشروع عليها بهدف توقيع المحاور الخاصة بالمنشأ على الخن