Basic knowledge of surveying
1. What is the concept of surveying?
Surveying: the study of the shape and size of the earth, and the science of determining the location of points on the ground
Including measurement and measurement design two parts:
Determination: use measuring instruments and tools to obtain a series of measurement data through measurement and calculation, or reduce the topography of the earth's surface into a topographic map
Survey and design: Mark the positions of the planned and designed buildings and structures on the ground as the basis for construction
2. Briefly describe the definition and characteristics of water level?
The surface of still water forms a gravitational equipotential surface called the water level
Its characteristic: a continuous surface perpendicular to the direction of gravity everywhere
3. What is the geoid?
The mean sea level replaces the still water surface and extends to the continent to form an irregular closed surface .
4. What are the reference planes and reference lines for measuring field work?
Geoid and plumb line
5. What are the reference planes and reference lines for measuring office calculations?
Reference ellipsoid and normal
6. What is absolute elevation (altitude) and what is relative elevation?
The height from a certain point to the datum, and the distance from a certain point to the geoid along the plumb line, usually called absolute elevation (altitude) -> Mount Everest measurement
The distance from a horizontal plane is called the relative height
7. What is the difference between the plane Cartesian coordinate system used in measurement and the coordinate system in mathematics? Why?
Answer: In the plane Cartesian coordinate system used in the measurement, the north-south line passing through the origin is the ordinate axis X, and the direction perpendicular to the X axis is the abscissa Y. The coordinate axes divide the plane into four quadrants, and the order is clockwise. Arrangement, the coordinates of each point stipulate that upward from the origin and positive to the right
Mathematically: In the coordinate system, the north-south line passing through the origin is the ordinate Y, and the direction perpendicular to the Y axis is the abscissa axis X. The coordinate axes divide the plane into four quadrants, and the order is arranged counterclockwise.
Because it is stipulated in the survey that the direction of all straight lines is measured clockwise from the north end of the ordinate axis, after this transformation, the mathematical formula will not be changed, and the calculation of the direction and coordinates in the survey will be facilitated
8. Features of Gaussian projection:
After the angles projected on the ellipsoid surface onto the plane are projected onto the plane, the angles are equal;
After the central meridian is projected, it is a straight line with the same length, and the other meridian projections are all symmetrical axes concave to the central meridian
The equator is also projected as a straight line, perpendicular to the central meridian, and the projections of the other latitudes are all symmetrical curves concave to the equator
9. How to divide the Gaussian projection
6° zone: Starting from the 0° meridian, it is divided into zones from west to east at intervals of 6° in longitude, and numbered sequentially from 1 to 60.
The relationship between the belt number N and the corresponding central meridian L0 is: L0=6N-3; N=[L/6°]+1; where L is the longitude of a place.
3° zone: starting from the 1.5° meridian, it is divided into zones from west to east at intervals of 3° in longitude, and numbered sequentially from 1 to 120. The relationship between the zone number n and the corresponding central meridian L'0 is: L'0=3° n; n=[L/3°+1]
11. What are the elevation system and geodetic coordinate system adopted uniformly in my country at present? Where is the origin of elevation in my country?
The elevation system adopted uniformly in China is called "1985 National Elevation Datum".
The geodetic coordinate system is called " 2000 National Geodetic Coordinate System" , and the origin of elevation is Guanxiang Mountain in Qingdao
12. What were the national elevation datums in 1956 and 1985?
72.289m，72.260m
13. What is the significance of replacing the horizontal plane with a water plane in the survey work, and what is the limit?
Within a radius of 10 km , when measuring distance, the water plane can be used instead of the level without considering the influence of the curvature of the earth on the distance. (10 km has no effect)
When the area P is 100Km² , when measuring the horizontal angle, the horizontal plane can be replaced by the horizontal plane without considering the influence of the curvature of the earth on the distance. (100 square kilometers have no effect)
Substituting the water level for the water level has a great influence on the elevation
Therefore, when performing height measurement, even if the distance is very short, the influence of the curvature of the earth on the height should also be taken into account
14. Regardless of any survey work, the basic elements of on-site measurement are:
Distance, angle, elevation , these quantities become positioning elements
It can be used to determine the plane position and three-dimensional space position of the point.
Height measurement, horizontal angle measurement and distance measurement are the basic contents of surveying,
Measuring height, horizontal angle and distance is the basic work of surveying
15. In order to limit the propagation of errors, measurements are usually made according to:
" From the whole to the part ", " control first and then detail ", the principle of " do not carry out the next measurement work without checking the previous measurement work "
height measurement
1. Elevation measurement : measurement work for determining the elevation of ground points;
Divided into leveling , triangulation elevation measurement , GPS elevation measurement , among which leveling measurement has the highest accuracy
2. Level measurement : Use the horizontal line provided by the level to measure the height difference between two points on the ground
Calculate the elevation of an unknown point based on the elevation of a known point
When the line of sight is horizontal, the readings a and b are respectively read on the scales at points A and B, then the height difference between the bright spots of A and B is equal to the difference between the readings of the two scales. That is: hab=ab. If the elevation of point A is known, and B is the point whose elevation is to be obtained, then the elevation of point B is: Hb=Ha+hab, let HA+a=Hi, which is called the instrument sight height, referred to as sight height
3. Steps to use the level gauge:
Rough Leveling -> Aiming -> Fine Leveling -> Reading
4. How does parallax occur? Steps to remove parallax?
When observing, move the eyes up and down slightly, if the scale image and the cross hair move relatively, that is, the reading changes, it means that there is parallax.
The reason for the parallax is that the target imaging plane does not coincide with the reticle plane, and the ruler image does not fall on the reticle plane.
Steps to eliminate parallax: Aim the telescope at a bright background, rotate the eyepiece focusing screw (adjust to the eye side first) to make the reticle very clear; aim at the target, and rotate the objective lens focusing screw (adjust to the target side later) to make the target image very clear
5. Leveling route: the route for leveling station observation.
Divided into: echo level route, closed level route, support level route.
Closed leveling route : a circular leveling routestarting and ending at the same known benchmarking point
Compatible leveling route: a leveling route starting and ending between two known advanced benchmarking points ;
Branch level line: starting from a known level point, the end point is neither closed nor attached to another known level point
6. The checks of leveling include calculation checks, station checks, and results checks.
There are usually two types of station checks : 1. The method of changing the height of the instrument; 2. The method of double-sided rulers (one side is red and the other side is black)