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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