Surveying Concept
1. The concept of surveying
Surveying is a science that studies the relative positional relationship between points on the ground (including ground, underground, and space).
Surveying uses measuring instruments and tools, and uses measuring methods and means to determine the relative relationship between points, mainly referring to the angle and distance relationship between locations. And between multiple points, they constitute the relationship between lines and surfaces .
Through calculation, the position of the ground point can be represented by coordinates and elevation data , and can also be represented by graphs , such as topographic maps, cross-sectional maps, etc., according to engineering needs.
2. The role of surveying
The surveying work mainly serves the national economic construction and provides all kinds of topographic maps for the national economic construction, as well as the required ground status measurement data, for the planning, design and management of industry, agricultural production, urban construction, national defense construction and various engineering construction, etc. Use; at the same time, it also provides accurate positioning of the site for the implementation of various engineering constructions .
In addition, in the fields of national defense, public security, earthquake and disaster monitoring, the cooperation of measurement work plays an increasingly important role.
3. Subject classification of surveying
Geodesy
Study large-scale positioning measurements around the globe or over vast areas , taking into account Earth curvature, gravity. Sub-conventional geodesy and satellite geodesy.
Topography
Research topographic maps and cadastral maps of various scales. It mainly studies the surveying and mapping of large-scale topographic maps in small areas.
Photogrammetry
Carry out aerial photography or remote sensing of the ground, and use ground images and spectral data to draw topographic maps.
Engineering Surveying
Study the measurement work and methods required for various stages of engineering design, construction, and operation. Cartography studies maps and topographic maps.
Basic tasks of surveying
1. Determination (ground-drawing)
Determine the current position of the ground. Measured results:
(1).Data
Coordinates (spherical coordinates, plane coordinates), elevation, angle, distance, azimuth, slope, area, etc. of the straight line on the ground. *
(2). Figure
Topographic maps, plans, cadastral maps, section maps, settlement maps, engineering drawings, etc.
2. Survey and design (drawing-ground)
—Stake out the plane positions and elevations of the buildings and structures designed on the drawings on the site as the basis for construction. Also called construction stakeout .
Measurement results:
A site sign reflecting the plan position and elevation of the design .
Features of Surveying
Characteristics and Requirements of Metrology
1. Features
Strong practicality and high responsibility requirements, must follow the norms and rules of measurement.
There are many contents: basic principles of surveying, error theory, instrument use, operation methods, basic calculations, etc.
2. Study requirements:
1. Learn and master the basic operation methods of measurement:
Angle measurement, distance measurement, height measurement
(Basic operation of the instrument, operating procedures, records, results arrangement)
2. Master the inspection and calibration methods of measuring instruments
(Axis relationship of measuring instruments, inspection and calibration methods)
3. Learn the basic operation methods of control survey, topographic survey and construction lofting
(Field Surveying, Office Calculation and Drawing)
4. Establish the basic concept of measurement error
(Master the basic theory of measurement error and the calculation of measurement error)
5. Other requirements
●Field operations: strictly follow the prescribed operations and operating procedures.
●Records: The handwriting is clear and correct, and shall not be altered arbitrarily
(altered according to the prescribed method).
●Calculation: According to the adjustment rules, check the calculation to ensure the calculation accuracy
(decimal places).
●Plus and minus signs: add "+, -" signs before the following data: height difference, vertical
angle, index difference, coordinate increment, all closure differences, correction number.
datum of surveying
Two datums are used for survey work:
geoid
The water level that coincides with the mean sea level
As the datum for establishing the elevation system , its elevation is zero
Noun: geodetic body, level surface, gravity equipotential surface (continuous curved surface perpendicular to the direction of gravity everywhere, and the surface is not smooth)
spheroid
——Smooth surface that can be expressed by mathematical formula, instead of the earth body, and very close to the earth body, the surface of the spheroid is used as the reference plane for establishing the coordinate system
An ellipsoid formed by rotating the ellipse PEP1Q around PP1 with the earth's rotation axis as the minor axis PP1
my country's 1980 geodetic coordinate system adopts:
a=6378140m
b=6356755m
Flatness f=1/298.257
Currently known: a=6378137m
b=6356752m
Flatness f=1/298.257
Determination of the ground position
Coordinates of the ground point
Three data represent a spatial point:
Plane coordinates X, Y (or spherical coordinates longitude, latitude), represented by the coordinate system
Height H, represented by the elevation system
Three representation methods:
1. Astronomical coordinates
2. Geodetic coordinates
3. Gaussian plane Cartesian coordinates
Using the Gaussian projection method, the surface of the spheroid is projected onto the plane for representation
(1) Measuring plane Cartesian coordinate system and point coordinates:
The Cartesian coordinate system of the measuring plane is shown on the right, and all plane trigonometry formulas can also be applied in the calculation of the measuring coordinate system
(2). Establishment of Gaussian plane Cartesian coordinate system
——Gauss projection method: project the ellipsoid onto the plane
Divide the projection zone on the ellipsoid surface -> project zone by zone onto the cylindrical surface -> expand the cylindrical surface into a plane Cartesian coordinate system
Features: Use conformal projection (ie conformal transformation, conformal mapping)
The central meridian of the projection zone is tangent to the cylinder, and its length remains unchanged during projection. After unfolding, it is the X axis , which is positive to the north; the equator is orthogonal to the central meridian, and after expansion, the Y axis is positive to the east.
(3). Representation of the Gaussian plane Cartesian coordinate system
For ease of use, move the X axis westward by 500km
(a) Add 500,000 meters to the abscissa with the central meridian as the x-axis; the ordinate remains unchanged
(b) In order to distinguish each coordinate zone, add the zone number of the coordinate zone before the abscissa of each point
Elevation of ground point
Elevation of ground point
Absolute elevation - the distance from the ground point to the geoid along the plumb line
Relative elevation—assumed elevation (mostly used in building construction)
Elevation System and Elevation Datum
China's National Elevation System : Yellow Sea Elevation System
China's National Elevation Datum : 1985 National Elevation Datum
my country takes the average sea level of the Yellow Sea near Qingdao as the geoid; it is artificially determined and relatively stable (in 1956, the average tide level of the first 6 years was taken as the geoid; in 1985, the average tide level observed for 26 years from 1953 to 1979 was taken as the geoid. as the geoid);
The origin of the level is built in Qingdao City, which serves as the national elevation datum of our country. The elevation of the 1956 elevation datum is 72.289 meters, and the elevation of the 1985 elevation datum is 72.260 meters.
Elevation system in Shanghai area: Wusong elevation system
Measurement Procedures and Principles
Basic Principles of Surveying Work
Layout: from the whole to the part
Accuracy: from high level to low level
In order: first control and then details
All measurement work must follow the above principles, which is also the working procedure of measurement
Procedures for measuring work
Three basic elements to determine the ground point position
Horizontal distance S
horizontal angle β
Height difference h
1. The relationship after the ground point is projected onto the horizontal plane
2. Height difference relationship between ground points
No matter how far apart the ground points are, their relationship in elevation is the height difference h.
The height difference h is used to determine (calculate) the height H of the ground point. If the elevation Ha of point A is known, as long as the height difference hab between point B and point A is measured, the elevation Hb of point B can be calculated:
Influence of Level Surface Curvature on Observational Quantities
In the small survey area, the horizontal plane is replaced by the horizontal plane, and the influence on the distance, angle and height difference is discussed.
Based on this, determine the maximum range where the horizontal plane can be used instead of the horizontal plane
Simplifies the calculation without affecting the accuracy
1. The influence of the curvature of the level surface on the horizontal distance
2. The influence of the curvature of the level surface on the horizontal angle
From conclusions 1 and 2, it can be seen that the plane measurement and calculation of general engineering within the radius of less than 10km does not need to consider the earth curvature correction
3. The influence of level surface curvature on height difference
Conclusion 3: When measuring height, even if the distance is very short, the influence of the curvature of the earth must be considered
Attachment: Units of measurement
1. Unit of length (name)
2. Area unit
3. Volume unit
4. Angle unit
The relationship between angles and radians