Showing papers on "Geodetic datum published in 2010"

The DNSC08GRA global marine gravity field from double retracked satellite altimetry

Abstract: Satellite radar altimetry has been monitoring the earth’s oceans from space for several decades. However, only the GEOSAT and ERS-1 geodetic mission data recorded more than a decade ago provide altimetry with adequate spatial coverage to derive a high-resolution marine gravity field. The original geodetic mission data suffer from degradation in quality and coverage close to the coast and in Polar Regions as well as the occasionally wrongly retracking of these, even in the open ocean. In order to improve the quality of these geodetic mission data and to derive a new improved global marine gravity field called DNSC08GRA, a new double retracking technique for analyzing the waveform data has been developed. Multiple retracking allows the system to retrack more data to increase the spatial coverage of the data. Subsequently, a second retracking run is used to enhance the SSH determination by using information from the first fitting to inform the second set of retrackers about smoothly varying sea state parameters. The development of the new global marine gravity field DNSC08GRA is described in this paper. Besides application of new retracking techniques the radar altimetry has been processed using EGM2008 as reference and augmented with ArcGP gravity data and laser altimetry from ICESat to close the Polar gap. DNSC08GRA is seen to perform significantly better than previous global marine gravity field like KMS02. The improvement in accuracy is better than 20% in general, but in coastal regions, the improvement is in many places of the order of 40–50% compared to older global marine gravity field KMS02.

Improved Constraints on Models of Glacial Isostatic Adjustment: A Review of the Contribution of Ground-Based Geodetic Observations

Abstract: The provision of accurate models of Glacial Isostatic Adjustment (GIA) is presently a priority need in climate studies, largely due to the potential of the Gravity Recovery and Climate Experiment (GRACE) data to be used to determine accurate and continent-wide assessments of ice mass change and hydrology. However, modelled GIA is uncertain due to insufficient constraints on our knowledge of past glacial changes and to large simplifications in the underlying Earth models. Consequently, we show differences between models that exceed several mm/year in terms of surface displacement for the two major ice sheets: Greenland and Antarctica. Geodetic measurements of surface displacement offer the potential for new constraints to be made on GIA models, especially when they are used to improve structural features of the Earth’s interior as to allow for a more realistic reconstruction of the glaciation history. We present the distribution of presently available campaign and continuous geodetic measurements in Greenland and Antarctica and summarise surface velocities published to date, showing substantial disagreement between techniques and GIA models alike. We review the current state-of-the-art in ground-based geodesy (GPS, VLBI, DORIS, SLR) in determining accurate and precise surface velocities. In particular, we focus on known areas of need in GPS observation level models and the terrestrial reference frame in order to advance geodetic observation precision/accuracy toward 0.1 mm/year and therefore further constrain models of GIA and subsequent present-day ice mass change estimates.

Airborne Gravity Field Determination

Abstract: Airborne measurement of gravity has long been a goal for geodesy and geophysics, both to serve geodetic needs (such as geoid determination) and in order to provide efficient and economic mapping of gravity anomalies for geophysical exploration. Although airborne gravimetry has been attempted since the 1960s (LaCoste 1967), it is only in the 1990s, with the development of carrier-phase kinematic GPS methods, that the accuracy has reached a useful level. In later years new gravity acceleration sensors and improved GPS processing methods have resulted in airborne survey accuracies of 1 mGal (10–5 m/s2) or less at a resolution of a few kilometers for several commercial operators (Williams and MacQueen 2001), typically operating in relatively small regions for geophysical exploration and flying during optimal conditions (e.g., at night when turbulence is minimal).

Combination of geodetic observations and models for glacial isostatic adjustment fields in Fennoscandia

Abstract: We demonstrate a new technique for using geodetic data to update a priori predictions for Glacial Isostatic Adjustment (GIA) in the Fennoscandia region. Global Positioning System (GPS), tide gauge, and Gravity Recovery and Climate Experiment (GRACE) gravity rates are assimilated into our model. The technique allows us to investigate the individual contributions from these data sets to the output GIA model in a self‐consistent manner. Another benefit of the technique is that we are able to estimate uncertainties for the output model. These are reduced with each data set assimilated. Any uncertainties in the GPS reference frame are absorbed by reference frame adjustments that are estimated as part of the assimilation. Our updated model shows a spatial pattern and magnitude of peak uplift that is consistent with previous models, but our location of peak uplift is slightly to the east of many of these. We also simultaneously estimate a spatially averaged rate of local sea level rise. This regional rate (∼1.5 mm/yr) is consistent for all solutions, regardless of which data sets are assimilated or the magnitude of a priori GPS reference frame constraints. However, this is only the case if a uniform regional gravity rate, probably representing errors in, or unmodeled contributions to, the low‐degree harmonic terms from GRACE, is also estimated for the assimilated GRACE data. Our estimated sea level rate is consistent with estimates obtained using a more traditional approach of direct “correction” using collocated GPS and tide gauge sites.

Etn@ref: a geodetic reference frame for Mt. Etna GPS networks

Abstract: In volcanology, geodetic data are one of the most important instruments for the scientific community interested in modeling physical processes related to magma movements in the shallow crust. Since the end of the 1980s, GPS surveys and continuous GPS stations have greatly improved the possibility of measuring such movements with high time and space resolution. However, physical modeling requires that any external influence on the data that is not directly related to the investigated quantity must be filtered. One major tricky factor in determining a deformation field using GPS displacement vectors and velocities is the correct choice of a stable reference frame. In this study, we defined a local reference frame using more than a decade of GPS measurements, to refer the Mt. Etna ground deformation pattern to a rigid block. In particular, we used a weighted least-squares inversion to estimate the Euler pole for the rigid block by minimizing the adjustments to two horizontal components of GPS velocity at 13 «fiducial» sites located within a 350-km radius of Mt. Etna. The inversion inferred a Euler pole located at 38.450˚N and C107.702˚E, and a rotation rate of 0.263 deg/Myr.

Investigation of topographic reductions and aliasing effects on gravity and the geoid over Greece based on various digital terrain models

Abstract: The reduction of gravity-field related quantities (e.g., gravity anomalies, geoid heights) due to the topography plays a crucial role in both geodetic and geophysical applications, since in the former it is an intermediate step towards geoid prediction and in the latter it reveals lateral as well as radial density contrasts and infers the geology of the area under study. The computations are usually carried out by employing a DTM and/or a DBM, which describe the topography and bathymetry, respectively. Errors in these DTMs/DBMs will introduce errors in the computed topographic effects, while poor spatial resolution of the topography and bathymetry models will result in aliasing effects to both gravity anomalies and geoid heights, both influencing the accuracy of the estimated solutions. The scope of this work is twofold. First, a validation and accuracy assessment of the SRTM 3″ (90 m) DTM over Greece is performed through comparisons with existing global models as well as with the Greek 450 m national DTMs. Whenever a misrepresentation of the topography is identified in the SRTM data, it is “corrected” using the local 450 m DTM. This process resulted in an improved SRTM DTM called SRTMGr, which was then used to determine terrain effects to gravity field quantities. From the fine-resolution SRTMGr DTMs, coarser models of 15″, 30″, 1′, 2′ and 5′ have been determined in order to investigate aliasing effects on both gravity anomalies and geoid heights by computing terrain effects at variable spatial resolutions. From the results acquired in two test areas, it was concluded that SRTMGr provides similar results to the local DTM making the use of other older global DTMs obsolete. The study for terrain aliasing effects proved that when high-resolution and accuracy gravity and geoid models are needed, then the highest possible resolution DTM should be employed to compute the respective terrain effects. Based on the results acquired from two the test areas a corrected SRTMGr DTM has been compiled for the entire Greek territory towards the development of a new gravimetric geoid model. Results from that analysis are presented based on the well-known remove-compute-restore method, employing land and marine gravity data, EGM08 as a reference geopotential model and the SRTMGr DTM for the computation of the RTM effects.

Unique Permittivity Determination of Low-Loss Dielectric Materials from Transmission Measurements at Microwave Frequencies

Abstract: A non-resonant microwave method has been proposed for accurate complex permittivity determination of low-loss materials. The method uses two measurement data of the magnitude of transmission properties of the sample. While the flrst datum must correspond to a frequency point resulting in a maximum magnitude of transmission properties, the other can be any datum at a frequency difierent than the flrst datum and not far distant from the flrst datum. Two closed-from expressions are derived for a good initial guess using the above data. The limitations of each expression are discussed. The method has been validated by transmission measurements at X-band (8.2{12.4GHz) of a low-loss sample located into a waveguide sample holder.

Optoelectronic Method for Structural Health Monitoring

Abstract: Important engineering constructions require geometrical monitoring to predict their structural health during their lifetime. Monitoring by geodetic devices, vibration-based techniques, wireless networks or with GPS technology is not always optimal; sometimes it is impossible as shown in this article. A method based on geodetic measurements automation applying local optical scanners for monitoring is proposed. Its originality and contribution is based on the novel method of precise measurement of plane spatial angles. It considers robust invariant AD-conversion angle-to-code for dynamic angle, signal energetic center search method, initial reference scale adjustment, and uncertainty decrease using mediant fractions formalism for result approximation. An algorithm of electromechanic parts interaction for spatial angle encoding with beforehand set accuracy is described. It is shown that by its nature it is appropriate for practically unlimited uncertainty reduction: it is only limited by reasonable ratio ‘‘u...

Median-Based Estimates and Their Application in Controlling Reference Mark Stability

Abstract: Control of reference mark stability is essential for monitoring of deformations of engineering structures or displacements of points in geodetic networks. Some robust estimates, which are based on median application, can be used for such purposes. For example, some R-estimates can be applied to determine displacements of geodetic points thus to identify unstable reference marks. However, such simplest approach can sometimes fail. Thus, a more complex strategy for monitoring of geodetic point stability is elaborated and presented in this paper. The concept presented here concerns leveling networks and applies some R-estimate and also other median-based estimates, i.e., the median distance to the median and the average distance to the median. The method proposed in this paper is illustrated with some practical examples and is compared with the traditional method for geodetic point stability monitoring.

Is Australian Data Really Validating EGM2008, or Is EGM2008 Just in/Validating Australian Data?

Abstract: The tide-free release of the EGM2008 combined global geopotential model and its pre-release PGM2007A are compared with Australian land and marine gravity observations, co-located GPS-levelling on the [admittedly problematic] Australian Height Datum, astrogeodetic deflections of the vertical, and the AUSGeoid98 regional gravimetric quasigeoid model. The results show that we cannot legitimately claim to truly validate EGM2008. Instead, EGM2008 confirms already-known problems with the Australian data, as well as revealing some previously unknown problems. If one wants to claim validation, then EGM2008 is validated because it can confirm the errors in our regional data. Simply, EGM2008 is a good model over Australia.

Sea level at Saint Paul Island, southern Indian Ocean, from 1874 to the present

Abstract: A data archeology exercise was carried out on sea level observations recorded during the transit of Venus across the Sun observed in 1874 from Saint Paul Island (38°41′S, 77°31 E) in the southern Indian Ocean. Historical (1874) and recent (1994-2009) sea level observations were assembled into a consistent time series. A thorough check of the data and its precise geodetic connection to the same datum was only possible thanks to the recent installation of new technologies (GPS buoy and radar water level sensor) and leveling campaigns. The estimated rate of relative sea level change, spanning the last 135 years at Saint Paul Island, was not significantly different from zero (−0.1 ± 0.3 mm yr−1), a value which could be reconciled with estimates of global average sea level rise for the 20th century assuming the DORIS vertical velocity estimate at Amsterdam Island (100 km distant) could be applied to correct for the land motion at the tide gauge. Considering the scarcity of long-term sea level data in the Southern Hemisphere, the exercise provides an invaluable additional observational constraint for further investigations of the spatial variability of sea level change, once vertical land rates can be determined.

Methods of pre-processing probe data

Abstract: Methods of pre-processing probe trace data include examining a sequential dataset for a route of travel between two points, identifying at least one anomaly in the sequential dataset, identifying at least one datum of the sequential dataset occupying a sequential position adjacent to the identified at least one anomaly, and inserting at least one non-anomalous datum to occupy a sequential position of the identified at least one anomaly in the sequential dataset, the at least one non-anomalous datum being determined based on one of extrapolation, smoothing and interpolation of the at least one datum.

Interpolation of Tidal Levels in the Coastal Zone for the Creation of a Hydrographic Datum

Abstract: As part of the U.K. Hydrographic Office (UKHO)-sponsored Vertical Offshore Reference Frames (VORF) project, a high-resolution model of lowest astronomical tide (LAT) with respect to mean sea level has been developed for U.K.–Irish waters. In offshore areas the model relies on data from satellite altimetry, while in coastal areas data from a 3.5-km-resolution hydrodynamic tide-surge model and tide gauges have been included. To provide for a smooth surface and predict tidal levels in unobserved areas, the data have been merged and interpolated using the thin plate spline method, which has been appropriately tuned by an empirical prediction test whereby observed values at tide gauges were removed from the solution space and surrounding data used to predict its behavior. To allow for the complex coastal morphology, a sea distance function has been implemented within the data weighting, which is shown to significantly enhance the solution. The tuning process allows for independent validation giving a ...

PCAIM joint inversion of InSAR and ground-based geodetic time series: Application to monitoring magmatic inflation beneath the Long Valley Caldera

Abstract: This study demonstrates the interest of using a Principal Component Analysis-based Inversion Method (PCAIM) to analyze jointly InSAR and ground-based geodetic time series of crustal deformation. A major advantage of this approach is that the InSAR tropospheric biases are naturally filtered out provided they do not introduce correlated or high amplitude noise in the input times series. This approach yields source models which are well-constrained both in time and space due to the temporal resolution of the ground-based geodetic data and the spatial resolution of the InSAR data. The technique is computationally inexpensive allowing for the inversion of large datasets. To demonstrate the performance of this approach, we apply it to the 1997–98 magmatic inflation event in the Long Valley Caldera, California.

ITRF to GDA94 coordinate transformations

Abstract: The Geocentric Datum of Australia 1994 (GDA94) is a static coordinate datum realised with respect to the International Terrestrial Reference Frame (ITRF) at the reference epoch of 1 January 1994. At this time GDA94 and ITRF were coinci- dent, however, as a consequence of the tectonic mo- tion of the Australian Plate, ongoing refinement of the ITRF and crustal deformation, the two reference frames have diverged and the absolute di¤erence between them is now approximately 1 m. Conse- quently, precise coordinate transformations between ITRF and GDA94 are required for many applica- tions, and in this study these transformations are reviewed, improved and extended. New transforma- tion parameters between ITRF and GDA94 are computed, including the specific ITRF realisations of ITRF1996, ITRF1997, ITRF2000, ITRF2005 and ITRF2008. The two most recent ITRF realisa- tions, ITRF2005 and ITRF2008, after transforma- tion have a root-mean-square di¤erence of less than 10 and 30 mm in the horizontal and vertical compo- nents, respectively, with respect to GDA94 at the Australian Fiducial Network (AFN) stations. How- ever, the magnitude of some residuals exceed 15 and 60 mm in the horizontal and vertical components, respectively, which reflects the accuracy limit of GDA94. Finally, the implications and future strat- egies for managing the di¤erences between GDA94 and ITRF are discussed, including novel coordinate transformation approaches and justifications for the modernisation of GDA.

Coordinate transformation by radial basis function neural network

Abstract: The Turkish National Geodetic Network (TNGN) datum (ED50) was changed to the Turkish National Fundamental GPS Network (TNFGN) datum (WGS84) in 2001 in parallel with the increasing use of GPS technology. Due to this reference frame change it became necessary to transform the existing coordinate information between ED50 and WGS84. The two-dimensional (2D) affine transformation is widely used for coordinate transformation. The objective of this study is proposing a radial basis function neural network (RBFNN) that has been more widely applied in function approximation as an alternative coordinate transformation method. 2D affine transformation (Affine) method and RBFNN are evaluated over a study area, in terms of the root mean square error (RMSE). The results showed that RBFNN transformed the plane coordinates (Y, X) of the check points with a better accuracy (± 0.011 m, ± 0.013 m, respectively) than Affine method and pointed out that RBFNN can be used for coordinate transformation. Key words: Coordinate transformation, artificial neural network, radial basis function, affine transformation.

Precise Geodetic Infrastructure: National Requirements for a Shared Resource

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Efficiency of robust methods and tests for outliers for geodetic adjustment models

Abstract: Geodetic measurements are commonly used for monitoring volcanic activities and crustal motions. Together with paleoseismic and other geologic observations, geodetic data are central in long-term forecast of earthquake hazards. Presence of outliers in geodetic data strongly affects least squares principle, which are extensively used for data analysis and modeling in geodesy. Thus, the positions of the geodetic points are computed as biased. Robust methods are techniques used to construct estimates describing well data majority. In this study, some robust methods and conventional tests for outliers have been tested on a number of linear and nonlinear geodetic adjustment models. The results are presented to illustrate the effectiveness of the methods. Furthermore, we discuss how the effectiveness of the methods changes depending on various key parameters for geodetic networks, i.e. the number of outliers, the magnitude of outliers, the degree of freedom, the number of observation and number of unknowns.

A back-propagation artificial neural network approach for three-dimensional coordinate transformation

Abstract: The European Datum 1950 (ED50) of the Turkish national geodetic network (TNGN) and the World Geodetic System 1984 (WGS84) of the Turkish national fundamental GPS network (TNFGN) are in use as geodetic reference frames in Turkey. According to the use of two reference systems, it is necessary to transform the three-dimensional (3D) coordinate data from ED50 to WGS84 or vice versa. The seven-parameter similarity transformation method is frequently used for 3D coordinate transformation in geodesy. In this study, a back propagation artificial neural network (BPANN) that has been more widely applied in engineering among all other neural network models is evaluated as an alternative 3D coordinate transformation method. BPANN is compared with a popular seven-parameter similarity transformation (Molodensky-Badekas) method over a test area, in terms of root mean square error (RMSE). The results indicated that the employment of BPANN transformed 3D coordinates (X, Y, Z) more accurate than Molodensky-Badekas method and can be useful for 3D coordinate transformation between ED50 and WGS84. Key words: 3D coordinate transformation, back propagation artificial neural network, seven-parameter similarity transformation, BPANN, Molodensky-Badekas.

Accuracy of 1908 high to medium scale cartography of Rome and its surroundings and related georeferencing problems

Abstract: Preliminary attempts to georeference maps of early twentieth century made by the Military Geographic Institute (IGM, the Italian geodetic agency) for the city of Rome and its surroundings, reported residual errors larger than errors observed on similar maps. Previous studies carried out on one or two century older maps of the same area, showed similar or even smaller errors (Baiocchi and Lelo 2005). Six sheets of the “City of Rome and its surroundings” map in scale 1:5 000 dated 1908 have been studied. The identified errors can be referred to the different system of geodetic projection and geodetic datum or to the derivation of some details from maps at smaller scale, but in this case historic documents seem to suggest a different explanation. Parameters useful to perform the transformation of the geodetic systems used in historical maps to modern systems are not known; for this reason until now the various attempts of georeferencing maps of this type were based on collimation of points recognizable on modern cartographies such as corners of historical buildings. This method has often given unsatisfactory results; therefore it was decided to proceed by determining the parameters for the transformation of geodetic datum. The history of geodetic systems used in Italy at the beginning of the 20th century is complex and, in the past, this has led some researcher to misinterpretations. For this reason a full explanation of geodetic systems used in Italy in this period is reported below. Since the parameters of the projection used for the maps in our case study are not known for sure, the reprojection was considered the only way for a correct georeferencing.

Numerical computation of soliton dynamics for NLS equations in a driving potential

Abstract: We provide numerical computations for the soliton dynamics of the nonlinear Schrodinger equation with an external potential. After computing the ground state solution r of a related elliptic equation we show that, in the semi-classical regime, the center of mass of the solution with initial datum built upon r is driven by the solution to ẍ = −∇V (x). Finally, we provide examples and analyze the numerical errors in the two dimensional case when V is a harmonic potential.

Spacetime Modeling of the Earth’s Gravity Field by Ellipsoidal Harmonics

Abstract: All planetary bodies like the Earth rotate causing centrifugal effect! The result is an equilibrium figure of ellipsoidal type. A natural representation of the planetary bodies and their gravity fields is in terms of ellipsoidal harmonics and ellipsoidal wavelets. Here, various effects are treated when considering the Earth to be “ellipsoidal”: Sections 2 and 3 start the chapter with the celebrated ellipsoidal Dirichlet and ellipsoidal Stokes (to first order) boundary-value problems. Section 4 is devoted to the definition and representation of the ellipsoidal vertical deflections in gravity space, extended in Sect. 5 to the representation in geometry space. The potential theory of horizontal and vertical components of the gravity field, namely, in terms of ellipsoidal vector fields, is the target of Sect. 6. Section 7 is concentrated on the reference potential of type SomiglianaPizzetti field and its tensor-valued derivatives. Section 8 illustrates an ellipsoidal harmonic gravity field for the Earth called SEGEN (Gravity Earth Model), a setup in ellipsoidal harmonics up to degree/order 360/360. Five plates are shown for the West-East/North-South components of type vertical deflections as well as gravity disturbances referring to the International Reference Ellipsoid 2000. The final topic starts with a review of the curvilinear datum problem referring to ellipsoidal harmonics. Such a datum transformation from one ellipsoidal representation to another one in Sect. 9 is a seven-parameter transformation of type (i) translation (three parameters), (ii) rotation (three parameters) by Cardan angles, and (iii) dilatation (one parameter) as an action of the conformal group in a three-dimensional Weitzenback space W(3) with seven parameters. Here, the chapter is begun with an example, namely, with a datum transformation in terms of spherical harmonics in Sect. 10. The hard work begins with Sect. 11 to formulate the datum transformation in ellipsoidal coordinates/ellipsoidal harmonics! The highlight is Sect. 12 with the characteristic example in terms of ellipsoidal harmonics for an ellipsoid of revolution transformed to another one, for instance, polar motion or gravitation from one ellipsoid to another ellipsoid of reference. Section 13 reviews various approximations given in the previous three sections. E-mail: grafarend@gis.uni-stuttgart.de

Outlier detection for geodetic nets using ADALINE learning algorithm

Abstract: Developed by imitating the operation of human brain, artificial neural network applications are used in many fields such as engineering, industry, medicine, agriculture, finance, communication, meteorology, space and aeronautics. By the help of sophisticated computing technologies, the learning algorithms used in artificial neural networks allowed solving many problems that remained as undecided and defied any mathematical expression, particularly in the fields of engineering. In geodetic studies, three-dimensional geodetic networks are used for all sorts of location-based engineering measurements on earth. Numerous measurements are performed to determine the position of the points in geodetic networks. Possible errors and inconsistencies in these measurements affect geodetic network precision. Therefore, the test for outliers is implemented to eliminate measurement errors and sort out outliers. In the present study, the test for outliers was performed on a computer program developed by using ADALINE learning algorithm and the results were compared with traditional methods (data snooping, Tau, t). This new method was observed to be superior to traditional methods with regards to calculations about outliers and decision-making on the results. Key words: Outliers, neural networks, ADALINE learning algorithm, geodetic nets.

Mean mesoscale global ocean currents from geodetic pre-GOCE MDTs with a synthesis of the North Pacific circulation

Abstract: [1] A new milestone in satellite geodesy is about to be completed with the expected availability of the high-resolution data from the already in-orbit Global Ocean Circulation Explorer (GOCE) satellite. There are still some open questions related to capability of recovering mean mesoscale (50 km plus) geostrophic circulation (MGC) patterns from observational Gravity Recovery and Climate Experiment (GRACE)-based geodetic Mean Dynamic Topography (MDTs), which we examine here in detail. A new set of global geodetic MDTs with high grid resolutions was computed (0.1° and 0.25°) based on the newest EGM08 and GRACE GGM02 geoid models. The high resolution coupled to good mesoscale feature discrimination was derived using efficient filtering procedure based on singular spectrum analysis. The new solutions were contrasted with five important MDTs, including the hybrid and the geodetic MDTs, through empirical orthogonal functions analysis, which permit the determination of the mutual correlation among the MDTs, and establishment of error bounds. The methodology made viable a detailed and robust analysis of the North Pacific Ocean circulation based on these MGCs including comparisons with known results from other studies. We prove the superiority of the geodetic EGM08 (as opposed to hybrid) MDT models by obtaining less noisy and more intense and slender western boundary currents and their recirculations, the bifurcations at the Shatsky Rise, and the known mean eddies in the low-latitude shear region (NEC-NECC).

Georeferencing of topographical maps using the software arcgis.

Abstract: The digital map must be built by using all the resources available based on a rigorous analysis of their content and the costs involved, having the purpose of reaching the necessary quality under conditions of maximum efficiency. Each data source implies the existence of specialized software which will bring that data in a digital map format, starting with insuring the necessary equipment, going through the technological problems and data conversion and ending with the proper training and preparation of the personal. Before using spatial data in Geographical Information System it is necessary to define spatial reference system that can establish with maximum accuracy the corresponding positions from earth. This can be done through a process called georeferencing process that can identify the ellipsoids and cartographical projections simulating the real space. The georeferencing process implies framing of a plan representation into a reference system called location. For georeferencing a map we need at least two pieces of information: a series of points easily identifiable on the map whose location (latitude and longitude, rectangular coordinates) is precise (here the principle is: "the more, the better") and the projection system where the original map on paper was made. The georeferencing process of the topographical maps based on known coordinates represents the most ordinary process of georeferencing a scanned map. This type of georeferencing process is used when we can accurately find the positions of the points on the surface of the map (usually a topographical map). During the time in Romania there have been used more projection systems, and the one used from 1971 until the present is Stereographical Projection 1970 on unique secant plan based on Krasowsy ellipsoid. Before using the georeferencing process, we must define the Romanian National Projection system into a CAD / GIS software. The parameters of this projection which will be used to input in the used software are: Code: Stereo 70; Description: Stereographical Projection 1970; Coordinate System Type: Geodetic; Datum: Pulkovo 1941 Russia (GIS and former USSR Teriritories); Oblique: Stereographic; Northing: 500000, Easting: 500000; Projection Parameters: Origin latitude: 46d , Origin longitude: 25d; Scale reduction: 0.9998.