Datum points are widely used, which can be used to help establish other datum features, and can also be used to help define the location of modeling features or the installation and positioning of components. Pro/ENGINEER Wildfire provides four types of datum points. Datum feature is the reference feature of part modeling, and its main purpose is to assist in the creation of three-dimensional features, which can be used as the reference surface for drawing feature sections, model positioning, control points and assembly. In addition, datum features (such as coordinate system) can also be used to calculate the quality attributes of parts and provide operation paths for manufacturing. Datum features include datum plane, datum axis, datum point, datum curve, coordinate system, etc.
According to the purpose, there are elevation datum points, gravity datum points and geomagnetic datum points. According to the position of reference point in the measuring system, it can be divided into relative reference point and absolute reference point.
What is the meaning of K in D=kl in civil engineering survey? Wow ~!
What is the construction benchmark in engineering survey? The datum of field survey is geoid, and the datum line is plumb line.
Datum line and datum plane
1. Datum line: Any object on the earth is affected by the centrifugal force and gravitational force generated by the earth's rotation, and the resultant force of these two forces is called gravity. The line of gravity action is usually called the plumb line. The plumb line is the datum line of survey work.
2. Datum: Determining the spatial position of ground points in the survey is achieved by establishing a coordinate system on the datum and measuring three basic quantities: distance, angle and height difference.
What is the basic concept of error in civil engineering survey questions?
1. Wrong definition:
Error = measured value-true value;
So the error is a value, mathematically a point on the coordinate axis, a signed value.
2. Error expression method:
① Absolute error:
Absolute error = measured value-true value (agreed true value)
In the verification work, the standard with high accuracy is often used as the true value to obtain the absolute error.
For example, if the secondary piston manometer is calibrated with a primary piston manometer, the indication value of the primary piston manometer is 100.5N/cm2, and the indication value of the secondary piston manometer is 100.2N/cm2, then the measurement error of the secondary piston manometer is -0.3N/cm2.
② Relative error:
Relative error = absolute error/true value X 100%%
The relative error has no unit, but it is positive and negative.
For example, if the first-class standard mercury thermometer is used to calibrate the second-class standard mercury thermometer, the first-class standard mercury thermometer measures 20.2℃ and the second-class standard mercury thermometer measures 20.3℃, then the relative error of the second-class standard mercury thermometer is 0.5%.
③ Quotation error:
Quotation error = indicated error/upper limit of measuring range (or specified value) x 100%
Citation error is a simplified, practical and convenient relative error of instrument indication.
If the working dynamometer with the upper range of 3000N shows 2392.8N when the calibration value is 2400N, its reference error is -0.3%.
3. Wrong classification:
(1) System error: the difference between the average value of the same measurement result and the measured true value under repeated conditions.
(2) Random error: the difference between the result and the average value when the same measured object is measured infinitely many times under repeated conditions.
③ Gross error: exceeding the expected error under specified conditions.
In civil engineering survey, the left disk is also called (), or () in civil engineering survey, the left disk is also called (front mirror).
In the construction survey, the reference point belongs to (). The answer is layout.
What are the measurement steps of 50CM line in civil engineering survey? How many steps? This is mainly the control line, which is convenient for setting out the axis, because sometimes after the formwork reinforcement is installed, the axis can't be seen, which is not conducive to setting out, so setting out the control line first and then the axis is also convenient for inspection, not necessarily 50, but also 70, 80, with a maximum of 1m, which is a problem of accuracy and a great error.
What's the difference between measurement and measurement in civil engineering survey? Measurement is to use elevation and coordinates to represent the site and points, and measurement is to mark the known elevation and coordinates on the site to guide construction.
What is the basic work of layout? Surveying (civil engineering survey) refers to the use of measuring instruments and tools to obtain ground point data through measurement and calculation, and to draw points and geometric shapes on the earth's surface into topographic maps. In the planning, survey and design stages of civil engineering, topographic data are needed first, so topographic maps of various scales are needed. After the completion of the project, it is necessary to survey the as-built drawings for acceptance and future maintenance management.
What is the leveling point in engineering survey, a standard concept! English name: leveling point English name: benchmark definition: elevation control points arranged at regular intervals along the leveling line.
Reference point (BM for short) is the control point in the elevation control network to measure its elevation through leveling. Generally divided into two categories: permanent and temporary.