Ugrás a tartalomhoz

Data acquisition and integration 2., Surveying (Geodesy)

Végső Ferenc (2010)

Nyugat-magyarországi Egyetem

2.6 Important measuring tools and equipments

2.6 Important measuring tools and equipments

Theodolite

A theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are mainly used for surveying applications, and have been adapted for specialized purposes in fields like meteorology and rocket launch technology. A modern theodolite consists of a movable telescope mounted within two perpendicular axes — the horizontal axis, and the vertical axis. When the telescope is pointed at a target object, the angle of each of these axes can be measured with great precision, typically to seconds of arc.

Figure 10. The soviet optical theodolite built in 1958

[9]

Depending on the accuracy and purpose, a distinction is made between

  • Theodolite (robust and light, about ± 10 " precision)

  • Tachymeter (including analogue distance measurement, since ~ 1990 mostly digital readout and automatic tilt compensation of the vertical axis)

  • Precision or Sekundentheodolit (± 1 ", for engineering geodesy)

  • And the universal instrument (± 0.1 ", for example DKM3 and wild T4) for astro-geodesy.

[10]

The basic plate or limbus contains the horizontal circle (1) and the vertical axis (S). He wears the alidade (Arabic), the top of theodolite consists of two supports (2), the horizontal tilt axis (K), the telescope (3), the circle reading (4) and the vertical circle (5). The telescope has a reticule (reticule in the eyepiece), by which the target axis (Z) is defined, and an internal lens to focus.

The base sits on the base plate which is mounted on a tripod and leveled with three leveling screws and spirit level. The centering of the measuring point is made by moving the instrument to the horizontal tripod plate, then tight by the mounting screw of the tripod from the bottom.

Figure 11. The surveyor’s tripod

[11]

The main Theodolite errors:

  • The trunnion axis is not perpendicular to the vertical axis.

  • The line of sight is not perpendicular to the trunnion axis.

  • The vertical axis is not plumb.

  • The vertical angle collimation is out of adjustment.

Total station

A total station is an electronic/optical instrument used in modern surveying. The total station is an electronic theodolite integrated with an electronic distance meter (EDM) to read slope distances from the instrument to a particular point.

Figure 12. Total station

[12]

Modern total stations are equipped with optional laser rangefinder that can measure on almost any reflector surface. Range and accuracy of this so-called DR measurement (direct reflex) are somewhat lower than that of the infrared measurements on triple mirror, so both methods are used side by side. The accuracy is mainly depend on the nature of the targeted surface in terms of its reflection properties (so the bright areas are far better than dark). The different tachometer models of the various manufacturers offer depending on the device class ranges from 15 to just over 2000 m.

Data processing

The measurement of destination (direction and distance) is fully automatic. For data storage are usually connected peripheral computer. In modern total stations are processors and corresponding memory often integrated. The data (three-dimensional measuring points) can now be exported in two dimensions using appropriate computer programs (such as architectural survey of facade / floor plans) and also mapped in three dimensions and as a dxf file.

Robotic total station

The latest generation of total stations has electrically driven lateral and vertical axes. These include allowing the automatic sighting of the triple mirror and target tracking. In addition, a total station can survey a series of several pre-defined points automatically. In this way, for example, the deformations of the arch dam or other constructions can be monitored.

Figure 13. The robotic total station with GPS receiver equipped

[13]

GPS is a "Global Positioning System." It is a technique for determining positions and elevations on earth. For maximum accuracy, a GPS total station takes help of a number of satellites. Depending upon the quality of the GPS survey equipment, the accuracy can differ from about +/- 30 meters for inexpensive hand held receivers, to only +/- 1 centimeter for sophisticated systems using a base station located at a known position on earth to give a reference signal. This technique is known as "differential processing".

Imaging total station

The total stations of the future rely on the use of visual information during the measurement. The test image is a partly used for documentation purposes, on the other hand, it can be actively integrated into the measurement process. The sighting of the points must no longer take the eyepiece, but can be made directly in the image. Digital zoom or optical zoom functions allow even the exact fine sighting. The measurement can to run from the tachymeter directly or via WLAN to the field computer or PC. Built-in scanning features allow the planar scanning of targets and thus help in creating photo-realistic 3D models.

Figure 14. The imaging total station

[14]

GPS and Laser scanner

Because the next chapter is fully about GPS and Laser scanner, we don’t discussing on it anymore.

Gyrotheodolite

A gyrotheodolite is used when the north-south reference bearing of the meridian is required in the absence of astronomical star sights. This mainly occurs in the underground mining industry and in tunnel engineering. A gyrotheodolite can be operated at the surface and then again at the foot of the shafts to identify the directions needed to tunnel between the base of the two shafts. Unlike an artificial horizon or inertial navigation system, a gyrotheodolite cannot be relocated while it is operating. It must be restarted again at each site.

Figure 15. Upper mounted gyrothedolite

[15]

The gyrotheodolite comprises a normal theodolite with an attachment that contains a gyroscope mounted so as to sense rotation of the Earth and from that the alignment of the meridian. The meridian is the plane that contains both the axis of the Earth’s rotation and the observer. The intersection of the meridian plane with the horizontal contains the true north-south geographic reference bearing required. The gyrotheodolite is usually referred to as being able to determine or find true north.[16]

Leveling instruments

A dumpy level, builder's auto level, leveling instrument, or automatic level is an optical instrument used in surveying and building to transfer, measure, or set horizontal levels. This has the leveling a telescopic sight, the target axis by means of a precision spirit level or similar device - now mostly a pendulum compensator - is aligned perpendicular to the perpendicular direction. The telescopic sight is perpendicular to the vertical axis free to rotate, therefore can be looked round with a horizontal line of sight. Any two points located in this horizon have the same height. A dumpy level is an older-style instrument that requires skilled use to set accurately. The instrument requires to be set level in each quadrant, to ensure it is accurate through a full 360° traverse. Some dumpy levels will have a bubble level ensuring an accurate level.

Figure 16. The functionality of dumpy level

[17]

The self-leveling instrument instead of the telescope level has a compensator (for the automatic leveling control of sight line). This consists of optical-mechanical components, which are inserted into the beam of the telescope. Through these components, the sight line is automatically horizontally in a small range. Because of the limited workspace of the expansion joints with a compensator, the bubble is required.

Figure 17. The principle of compensator

[18]

A digital electronic level is also set level on a tripod and reads a bar-coded staff using electronic laser methods. The height of the staff where the level beam crosses the staff is shown on a digital display. This type of level removes interpolation of graduation by a person, thus removing a source of error and increasing accuracy.

Figure 18. Digital electronic level instrument

[19]

Figure 19. Accurate invar bar code leveling staff

[20]



[9] http://en.wikipedia.org/wiki/File:SovietTheodolite.jpg

[10] http://de.wikipedia.org/w/index.php?title=Datei:Theodolit_Schema.PNG&filetimestamp=20051123023705

[11] http://en.wikipedia.org/wiki/File:Surveyors_tripod.jpg

[12] http://en.wikipedia.org/wiki/File:Teodolit_nikon_520.jpg

[13] http://www.thetestequipment.com/articles/gps-total-station.html

[14] http://www.siteprepmag.com/Articles/Products/2010/10/05/Leica-Reveals-Viva-TS15-Robotic-Imaging-Total-Station

[15] http://www.ismdhanbad.ac.in/depart/mining/facility.htm

[16] http://en.wikipedia.org/wiki/Theodolite

[17] http://www.answers.com/topic/dumpy-level

[18] http://en.wikipedia.org/wiki/File:Automatic_Level.svg

[19] http://www.surveyequipment.com/levels/digital-levels

[20] http://www.tradevv.com/chinasuppliers/zfyqyb_p_1716e8/china-Accurate-invar-bar-code-leveling-staff-top-shell.html