REALIZATION OF A GPS PROJECT

For the realization of works using the GPS method, it is necessary to know the possibilities offered by the hardware and the available software, the procedures of observations will be stopped accordingly.
-A good performance requires
-a good project design
- good preparation and planning of the mission;
-a rational use of GPS receivers;
- a mastery of the data processing software.

1-STUDY AND PROJECT DESIGN

1-1 Study and establishment of the preliminary project

 For the preparation of the preliminary project of attachment and / or survey, the following documents must be available:

- The topographic map,

- the list of coordinates of the geodesic points,

- the cadastral maps of the area.

- the cadastral maps of the area.

The geodetic points are transferred and the cases to be surveyed are collected on topographic maps and cadastral maps.

The choice of new points will take into account the position of the nearest old points

surrounding the work site to ensure good homogeneity.

A minimum of three old points is necessary, whatever the mode of observation used. This number of points may increase depending on the size of the project. A good geometrical configuration must be ensured. If registration is very important in the work area and

if there are no geodetic points, the connection will have to be done on already stationed borders bordering the work site.

1-2 Preliminary selection of observation methods

After approval of the preliminary project, the observation mode is stopped according to the length of the baselines:

- Static mode can be used for short and long baselines without

however, exceed 15 km with single-frequency receivers.

- Fast static mode for baselines less than 10 km.

Stop & Go kinematics or pseudo-kinematic modes for the survey of terminals and

details of the properties. In these cases, baselines should be less than 1 km.

2- RECOGNITION AND MATERIALIZATION

2-1 Recognition of the points of support

This recognition aims to ensure the existence and stability of the points of support

(conservation of the signal, the underground mark and the boundaries, etc.) as well as the homogeneity of the

network (same system). For this, GPS observation sessions can be dedicated

at the points of support, and their treatment immediately carried out.

The control of the points of support will be done on the basis of the comparison of the gaps between the old

and the new coordinates obtained successively each time we fix the coordinates

one or more points.

2-2 Recognition of properties to be lifted

For the design of the project of attachment and survey, it is proceeded to the recognition of the properties to be lifted and properties riparian already lifted.

2-3 Choosing the location of new points

The location of the new points should be chosen as far as possible in order to guarantee

their conservation, facilitate their accessibility while trying to ensure intervisibility between

points in the network so that they can be reused in subsequent topographic

conventional survey methods. These points must be far from the high voltage lines,

places with high magnetic density, radio stations and reflective surfaces.

In addition, an unobstructed view must be provided from 15 ° elevation.

2-4 Materialization

The new points will be materialized according to the instructions in force. A fact sheet or identification is established for each materialized point.

3-DEFINITIVE PROJECT AND ADOPTION OF OBSERVATION METHODS

Taking into account the results of the recognition, the final project is drawn up and the observation processes are stopped

- Taking into account the results of the recognition, the final project is drawn up and the processes

of observation are stopped

- Static mode when baselines are greater than 10 km and static mode

fast when baselines are less than 10 km.

It is recommended that baselines form closed polygons (loops) for

control needs.

 4- PLANNING

The planning software includes options that, after entering the coordinates

geographical location of the work site, to generate for a given period, documents

the number of visible satellites and their PDOPs as well as their azimuths, elevations,

constellation changes, celestial view, etc.

On the basis of these documents, appropriate periods are chosen for the collection of

observations and the scheduling of observation sessions.

5- OBSERVATIONS

Precautions to take before making observations

Collection of observations

Survey of terminals and details.

6- TREATMENT AND CONTROL

Processing GPS observations

Loading GPS data

Baseline processing

Qualification of baseline results

 Network adjustment

Analysis and evaluation

The results obtained at the end of the definitive compensation must answer the clarifications

required for the establishment of the points of attachment and survey cadastral plans.

The maximum error allowed on the coordinates of the points of attachment shall not exceed

10 cm.

The maximum difference allowed between the two determinations of the coordinates of the terminals is from 4 to 5