Aim:
    
     GPS (Global Positioning System) technology can be used in different activity fields. Regarding the specialized works in surveying, cadastre, geodesy and GIS, GPS functionality has been proved in works like the following:

      Geodesy:

• Support networks;

     Land survey and cadastre:

• Testing the coordinates of the new points and the terrain lining out of the known coordinate points;
• Collection of data and control of the land situation;
• Parceling and surface detachments.

     GIS:

• Collection of GIS/Mapping data;

     Agriculture:

• Parceling;
• Surface detachments;
• Terrain systematization for crops;
• Controlling cultivated areas – extremely important in the context of EU financing for cultivators.

     Utilities companies (electrical networks, water, gas, phone, petrochemical industry, and so on):

• Testing the water flows, pipe paths, cables and so on;
• Collecting data regarding the geography of the paths areas.

     Forestry:

• Forestry cadastre;
• Data collection and control over forests;
• Forestry inventory;
• Parceling and surface detachment.

Activities developed by the company:

     After establishing the starting period, the implementation, the delivery of the service, the costs, Office of Cadastre and Land Registration (OCPI) fees and paying method the following stages are to be tracked:

Field-work stage:

     In this stage all the necessary surveying measurements will be effectuated to test the points of the terrain coordinates, materialized or not.
     Regarding the lining out works RTK (Real Time Kinematic) technology is being used as a field-work method, together with measurements and real-time setting outs by visualizing the online coordinate received from satellites and corrected by the reference station or GPS base, hereby the system assures a testing precision of the point of 1.5 – 2.0 cm.

Office stage:

     In this stage the post-processing of the terrain measurements and the dossier will be created in conformity with the specific and the character of the completed work.

OCPI reception stage:

     Subsequently the dossier drawing up phase, this will be deposit to OCPI (Office of Cadastre and Land Registration) as the estate to be verified, receipted and registered in the cadastral register.

What GPS means?

     GPS resides in a satellites network that is orbiting around the Earth, these forming the GPS network. The satellites were emplaced in space in order to be used for military purposes by the Defense Department of the US Army, but currently these are being used also by civilians.
     Nowadays, the satellite group is a responsibility of US Airline Force and the maintenance and replacement goes beyond 700 milliards annually. US Government doesn’t fees the usage of GPS services; the only costs are those of the users and are related to the acquisition of the GPS receptors.
     Although GPS technology has began to be rapidly and intensively used, even in Romania, one can find that the general principles on which basis these are functioning are yet relatively little known and sometimes even ignored. This situation can lead to exaggerating GPS technologic performances (“if something has been measured with GPS that means that the results cannot be wrong”) but also to the insufficient and inefficient exploitation of the given possibilities.

GPS precision.

     GPS testing are affected by numerous errors (the imprecision of the orbit parameters, accidental deviation from orbit, time inaccuracy, the relatively unfavorable position of the utilized satellites for testing, deviances of the radio wave from the theoretical trajectory because of the heterogeneously environment that it sweeps and so on). Due to this, the “absolute” position of a point can be tested, in the best case, with a millimeter error. Instead, can be tested with sufficient accuracy (centimeters and even millimeters) relative positions (distances) of the points that were simultaneously measured using the same satellites configuration (in which case the errors are being reciprocally annulled). This situation, justifies, among others, the processing of the GPS testing as lengths measurements similar with the trilateration networks.

Coordinates transformations.

     Given a definite case for our country, amongst the points of the tested network by GPS observation there are also known points from the geodetic national network which are stationed in order to facilitate the transformation of the new points coordinates in the national system. It is recommended the disposition of the common points of the both systems to cover as best as possible the whole area of the new network. The feasible transformations depend mostly by the information on which we dispose of for the common points. From this point of view we can dispose of:

• Points of which three-dimensional position is known;
• Points of which plane-metrical position is known;
• Points of which altimetric position is known.

Implications of GPS utilization.

     GPS technology utilization has some advantages which deserve to be mentioned:

• Mostly constant precisions, regardless the distance between points;
• The visibility between points is not mandatory;
• Dates can be processed even on a minicomputer;
• Low costs.

     Subsequently the processing of the taken measurements (X, Y, Z) coordinate are obtained and/or (B, L, h) and the testing precisions of those. Regularly, X, Y coordinates are required for 1970 stereographic projection Krasovsky ellipsoid, normal h altitudes referred to Black Sea 1975 and the testing precisions of these given.
     Very often are made some statements that are at least arguable, as this one: if by GPS surveillances processing one can obtain good precision this means that also the coordinates in the 1970 stereographic projection plan are also good; GPS technology utilization is a guarantee for meeting the ANCPI tolerances.
     The obtained results using GPS technology are influenced by some elements that can be described below:

• The geometry of the network. In this case one has to consider the number of GPS stations, their configuration and the bases (data bases?) that are being formed;
• The geometry of the satellites. In order to obtain good results one has to know and to set up the number of satellites that are going to be observed from every station, their configuration, the minimum elevation number below which the GPS observations are not going to be taken in consideration anymore;
• Receptors. The utilized receptors are an important factor that should be considered when one finds to obtain good result by using this kind, their number, their configuration for every session, the atmospheric conditions when the measurements are taken and so on;
• Considerations regarding the time. In order to lessen the ionosphere influences the observations must be effectuated in a certain period of the day. Also the time length assigned for measurement and the pre-processing conditions must be settled;
• Observing method. The method of considering the GPS observations (pseudo rangessau carrier phase or both) and the frequencies (L1, L2 or both) are important;
• The processing method. One has to settle the “datum”, the way the observations are processed and if one considers the network or just the measured bases, the utilized ephemeredes (broadcast or precise), and so on;
• Work organization. It is obvious that an important factor for the success of the operation is that refereeing to the auxiliary part, meaning the number of the individuals that are participating in the measurement, the transport methods from A to B, other necessary equipments for the observation campaign.

     A transformation in space with three dimensions of the Cartesian or geodetic coordinates that are obtained as a result of the GPS observations processing does not always leads to a satisfactory value for the coordinates in 1970 stereographic projection plan and for normal altitudes, because:

• There isn’t a clear-cut data regarding the altitudes system (Black Sea 1975, Baltic Sea, and so on), and it happens very frequently that one to receive altitudes that are presumably referred to Black Sea and later on one to notice that these are identical with those on the maps;
• The altitudes of the triangulation points are imprecise for the tracked aim these being determined through trigonometric leveling (and are not obtained as a result of a rigorous processing);
• Unfamiliarity regarding the compensation algorithm utilized in software and the constraining parameters.

     A second possibility to obtain the coordinates in the 1970 stereographic projection system is to process by using the indirect observation method the GPS measured distances. The problem in this case is that to find if the applicability condition are being met and this without involving supplementary works. One can assert on a quick glance that:

• Distance measurements are always sufficient (the effectual instructions are stipulates that every GPS determined point to converge at least 3 measured bases);
• The obtained angled distances by using post-processing are very precisely determined;
• The temporary coordinates in 1970 stereographic projection are known precisely enough (from a 3D transformation);
• The altitudes of the necessary points for distance reduction of the projection plan are known with a sufficient precision (from the same transformation).