DEPT. OF GEOGRAPHY & RESOURCE DEVELOPMENT

LECTURE 3

Methods of Cartographic Data Collection

Theodolite & Total Station Survey

GEOG 214

TOPICSIntroduction to the TheodoliteDescription and use of the TheodoliteIntroduction to the Total StationUsing the Total StationFieldwork

Figure 5.1 Types of Theodolite

The earlier type of Theodolite

Figure 5.2 The labelled T16-84 Theodolite

Fixed base (called trivet) with a tribrach, Alidade which is the movable upper part Telescope, the base with the tribrach is fixed tightly to the top of the Tripod and it is levelled by means of Foot screws and well as adjusting the legs of the tripod. Description of the Theodolite

The telescope containsEyepiece lens

Object lens. The line joining the centres of these lenses is called the sighting axis (line of sight)

The instrument is roughly levelled on the tripod by adjusting the legs of the tripod and using the foot screws to bring the circular bubbles fitted to the base to the centre.

INCLUDED ANGLESURVEY STATION (TEMPORARY BENCHMARK)

Theodolite Booking Instrument stationBack stationForward stationFace and swingHCR (Height of Collimation)Include angleDifferenceRemarks

Table 5.1 Booking of Theodolite Station Data

InstrumentstationBackstationForwardstationFace andswingH.C.RIncludedangleDistance(m)RemarksAB

LECTURE Total Station -TS

BackgroundRapid technological advances particularly in electronics, a number of cartographic and surveying equipments have been more acceptable as More modern, accurate surveying equipment.

The equipment looks similar to the manual theodolite and the tacheometer and therefore shares with them some of their operating principles

The features and in-built abilities of the total station make work more flexible and less tedious The TS makes surveying less time consuming and has a very high degree of accuracy compared to the other instruments used in land surveying.

TS - a combination of:

Electronic transit /TacheometerElectronic Distance Measuring device (EDM) Computerized systemskeyboard, software for editing, download, storage and display. Reflective Prism

Figure: The Total Station

TOTAL STATION MOUNTED ON TRIPOD

Reflective Prism on Tripod

Front view of a Total Station

The rear view of a Total Station

Source: Compiled from the web

It is by no means a replacement of the old methods but rather, the old familiar procedures have been integrated into what is referred to as field-to- finish surveying system

automated more efficient less time consumingFIELD-TO- FINISH System

Principles of Operation -2An electronic theodolite with telescope for measuring angles between stations.An electronic distance measuring (EDM) system which enables accurate measurement of distances Computerized input/output system/interface (keyboard, in-built rechargeable battery, software for editing, download, storage and display)

The Telescope System

A standard transit is basically a telescope with cross-hairs for sighting a targetAttached are scales for measuring the angles of rotation After rotating the telescope to aim at a target, one may read the angle of rotation and the angle of inclination from a scale. The electronic transit provides a digital read-out of those angles instead of a scale The readout is continuous; so angles can be checked at any time.

The EDM System

The electronic distance measuring device measures the distance from the instrument to its target. The EDM sends out an infrared beam which is reflected back to the unit, and the unit uses timing measurements to calculate the distance traveled by the beamWith few exceptions, the EDM requires that the target be highly reflective, and a reflecting prism is normally used as the target.

Calculating System

The TS also includes a simple calculator to figure the locations of points sighted

The calculator can perform the trigonometric functions needed, starting with the angles and distance, to calculate the location of any point sighted.

Calculating System

The TS station also includes a simple calculator to figure the locations of points sighted

The calculator can perform the trigonometric functions needed, starting with the angles and distance, to calculate the location of any point sighted

Data Recording

Many total stations also include data recorders.

The raw data (angles and distances) and/or the coordinates of points sighted are recorded, along with some additional information

The data thus recorded can be directly downloaded to a computer at a later time.

The use of a data recorder further reduces the potential for error and eliminates the need for a person to record the data in the field.

The determination of angles and distance are essentially separate actions. One aims the telescope with great care first; this is the part of the process with real potential for human error. When the telescope has been aimed, the angles are determined. Only then does one initiate the reading of the distance to the target by the EDM. That takes only a few seconds; the calculations are performed immediately.

Function of the Total Station 1

It also has a rechargeable battery which enables continues field work without having to break to charge the battery. The TS unlike the theodolite also has a keyboard which enables digital/automatic input of back and forward stations. It has an on-board software makes the necessary adjustments to the calculations to reduce slope distances to their horizontal and vertical components. The calculation of included angles is done automatically by the total station.

Function of the Total Station - 3

The total station has a face left or right depending on the position of the station to be sighted, as in the case of the theodolite

INCLUDED ANGLESURVEY STATION (TEMPORARY BENCHMARK)

Function of the Total Station - 3The keyboard also serves an additional purpose of editing when necessary.It also has an input memory system which enables it to store information to be used at a later date. The TS also has an external part which enables a computer to be connected to it back at the office to enable further calculations and plotting. Thus, data from the TS are down-loaded into a laboratory computer that possesses data analysis, editing and plotting capabilities.By combining TS data with information held in existing spatial databases, you have the power to produce a variety of finished maps.

Function of the TS - 4

The TS with the above features enables accurate field-to-finish survey where angles can be measured and included, angles calculated even on the fields. It automatically measures and displays distance and direction data (both horizontal and vertical angles), and transmits the results to its computer. It also facilitates the measurement of distance from the instrument station to the back or forward station, an activity that would have been done using a chain if the theodolite was being used. The TS also has an additional advantage of ensuring more accurate traversing to be done in the end and further changes made when necessary and at a later date.

Using the Total Station -1 A total station automatically measures and displays distance and direction data (both horizontal and vertical angles), and transmits the results to its in-built computer.

The on-board software then makes the necessary adjustments to reduce slope distances to their horizontal and vertical components.

If a station of oordinates (x, y, z) and a back sight azimuth are entered into the instrument, the coordinates of the sighted point can be computed and displayed.

Using the Total Station -2Data from the Total station are downloaded into a laboratory computer that possesses data analysis, editing, and plotting capabilities.

By combining total station data with information held in existing spatial databases, you have the power to produce a variety of finished maps.

Operational Technique of the TS

Set instrument on a tripod at a known TBM to serve as instrument station.

You are already aware of the tripod and how it is used Identify the Back station (A) and Forward station (B)

Locate a back station and face the telescope towards the station (face left or face right)

INCLUDED ANGLESURVEY STATION (TEMPORARY BENCHMARK)

Field Procedures -1From the above, A is the back station and B the forward station. The angle (?) which is known as the included angle is calculated by the total station by subtracting B from A. The coordinates of A and B are measured by the total station in degrees, minutes and seconds.

Field Procedures -2In-put the angle of the back station into the system using a keyboard after reading from the graduated card at the base of the instrument through a lens (telescope)Turn the instrument without moving towards the forward station and record the angles also.Command the system to calculate the angle between the two stations using the keyboard and record distance between instruments station and back or forward station

Field Procedures -3The same procedure can be repeated until all the recordings in the series are completed.Set up/Level TS on tripodMount/Set up the reflective prismSight with the telescopeTake readingsMake recordingsIdentify and address field problems and challengesDownload data and use

The reflective prism The reflective prism is mounted so that its reflection point is aligned with the center of the pole on which it has been mounted. Although the tip of the pole is placed on the point to be surveyed, the instrument must be aimed at the prism so it will calculate the position of the prism, not the point to be surveyed. Since the prism is directly above the tip, the height of the pole may be subtracted to determine the location of the point. That may be done automatically. The pole must be held upright, and a bubble level is attached to give the worker holding the pole a check. It is not as easy as one might expect to hold the pole upright, particularly if there is any wind; as a result, multiple readings may be required.

Making measurements

When the instrument is set up and turned on, it sets itself to be pointing to zero degrees (north) when power is first supplied. There are two adjustment knobs for rotating within the horizontal plane. One rotates the telescope to make a sighting, with the readout of angles displaying changes. The other, however, permits the user to rotate the entire instrument and to keep the current angle unchanged during the process. That effectively re-orients the zero or north setting. That can be very helpful when setting up or re-setting the instrument. Thus, it can be devastating if one makes that adjustment by mistake and thereby changes the north setting. The survey information can be recorded by hand, and the data then entered into the AutoCAD model. Recording could be done in a field notebook or stored in the system memory to be assessed at a later date. This process is not necessary if a data collector with the most modern of capabilities is available. The data collector can automatically orient all new points to a pre-existing set of survey coordinates.

ConclusionIn a land survey the feature and in-built abilities of the total station makes work more flexible and less tediousAs you can see, the use of the chain or compass, or even the mechanical theodolite becomes unnecessary when you use the TSThe total system is a most effective and accurate method of traversing that facilitates the work of the modern surveyor. It is indeed a Field to Finish System