Basic Concepts: Surveyor Instruments

The instruments generally used in topography are the total station and the site level.

-the total station allows to measure horizontal angles, vertical and distances (the theodolite him, only measures horizontal and vertical angles).

-The level of construction allows to calculate differences of altitudes.

The total stations

1. Setup

The setting up consists of placing the apparatus on the one hand vertically of the station and on the other hand in a horizontal plane.

To achieve this, the approach is as follows:

1.1 The tripod

After opening and unfolding the tripod, install it above the station. A simple principle is to intersect the ground projections of the tripod's three branches on the station point.

1. 2 Coarse calibration with spherical level

The camera is fixed on the tripod tray. It must now be centered vertically in a horizontal plane.

1.3 Fine adjustment with the toric level

The tacheometer and the tripod are firmly attached, the legs of the tripod are stable and tight, the camera is perfectly vertical to the station and the spherical level is adjusted. It is now a question of finishing this setting thanks to the toric level. (all instructions on the document)

2. sights and surveys

2.1. directions

When the unit is fully stationed, we can proceed with the survey of the land.

note the horizontal angle of another "stable" reference, distance ...

BN: For the sake of argument, it is estimated in topography that an angle difference of 1 mgr corresponds to 100 m to an error of 1.6 cm.

2.2. Aimed at a prism with a total stations

3. Slope distance and reduced distance to the horizontal

The inclined distance is that measured on the ground (along the distance-meter / reflector axis).

The reduced distance to the horizontal is the one actually separating two points: it is therefore the one that is plotted on the plane. V = vertical angle

Di = inclined distance

DH = reduced distance to the horizontal

DH = Di sin V

4. Altitude of a point

V = angle vertical

Di = distance inclinée

DH = distance horizontale

Ht = hauteur de l’instrument

∆H = différence de hauteur de la visée

Hp = hauteur du prisme

Zs = altitude connue de la station

Zp = altitude du point visé (à déterminer)

∆H = différence de hauteur de la visée

Zs = altitude connue de la station

∆H = Di cos V

Zp = Zs + Ht + ∆H – Hp

Zp = Zs + Ht + Di cos V –Hp

Zp = altitude du point visé (à déterminer)

The level of construction

The site level is used to measure heights on a graduated rule (the chart) and by calculation to determine differences in altitudes between points.

1. Setting up a site level

Stationing involves placing the unit in a horizontal plane. same notion of total station

2. The sights

The sights are by definition horizontal and the readings are made on a test pattern by reading the graduation of the horizontal and main reticular wire.

3. Determination of differences in altitude

The determination of the differences of altitudes is calculated by a simple subtraction between the reading on the reference (Lref) and the reading on the point to be measured (Lp).