Sorvey Definitions

# Sorvey Definitions

### La topographie (du grec topos = lieu et graphein = dessiner) est la science qui permet la mesure puis la représentation sur un plan topographique terrain ou une carte des formes et détails visibles, qu'ils soient naturels (notamment le relief et l'hydrographie) ou artificiels (comme les bâtiments, les routes, etc.)

INTRODUCTION
1. GENERAL

1.1 Whay this course in topography ?
It is a question, for you nfuture technicians of being brought to solve problems of installation or civil engineering. Which boils down to :
Know how to read a  Tioigraphic plan,
To be able define the characteristics of the plans that they will execute,

₪ Be able to carry out topographical operations in the field.

1.2 Définitions

₪  GEODESY : it is the science that studies the shape of the earth. By extension, it brings together all the techniques aimed at deteminning the planimetric and altimetric positions of a certain number of geodetic points and  benchmarks.

₪  TOPOGRAPHY : the word topography comes from the Greek topois (the place) and graphein (to describe).
Topography is the set of operations that allow the graphic representation of the configuration of the land with all the details therein by neglecting the curvature of the earth without significant repercussions for areas with a radius of less than or to 10 km.

2.   UNITS

2.1 Distances

METRE (m) : SI unit length equal to the path length traveled in vacuum by light for a duration of 1/299,792,458 th of a second.

### ₪Multiples

megameter      (Mm)
Kilometer         (km)
Hectometre      (hm)
Décameter       (dam)

### ₪Submultiples

Decimètre         (dm)
Centimèter       (cm)
Millimeter         (mm)
Micrometer      (μm)
Nanometer      (nm)

2.2 Surfaces
METRE-CARRE ()
HECTARE (ha)
Area equal to 100 × 100 m i.e. 10 000

2.3 Angles
RADIAN : (rad ou rd) unité SI unit. The tradin is a geometric unit of plane angle of the SI.

DEGREE : (°) its value in SI.unit. is π / 180 rad
GRADE : (gon) its value in SI.unit.  is π / 200 rad

3.  NOTIONS OF SCALE
The scale of a plan is the constant ratio between the graphic length on the plan and the same horizontal length on the around, in the denominator, the smaller the drawing.

4.  CANVAS

4 .1 The LAMBERT system

In order to estabish plans with satistactory precision, it was absolutely necessary to determione throughout the territory a certain number of clearly visibvle points which would serve as support for current topographical measurements.
In France, IGN.  opted for the LAMBERT system (conical projection) thus creating a LAMBERT grid.
This grid makes it possible to designate all these points by their rectangular coordinates ( Y , Y ). To avoid excessive deformations, France is divided into four zones :
In France there are nearly 100,000 points making up the geodetic network. They are all visible from each other, and are therfore located high up. All shese points are marked on notebooks and data sheet are made available

4.2 The IGN69 network
In parallel with the geodesic network, the altimetric canvas was created :
4000,000 landmarks measured at altitude. Any topographic point can be obtained from this canvas con stituting the NGF. (General leveling of France).
Altitudes are level, determined by t-he Marseille tide gauge.
IGN map extract at 1/25 000th