This paper provides an introduction to multiple regression equations as a method of performing geodetic datum transformations. The formulae are particularly useful when there are non-linear ...distortions that need to be built into the transformation model. However, the equations take the form of a one-way transformation, usually a local geodetic datum to a global datum. The standard procedure for applying the equations to obtain the reverse transformation only gives approximate results relative to the original model. This paper quantifies the problem and describes three methods for computing the reverse transformation (or inverse transformation) more accurately.
For three-parameter datum transformations to be applied rigorously, geodetic coordinates on the first ellipsoid need to be converted to Cartesian coordinates before application of the shifts, then ...converted to geodetic coordinates on the second ellipsoid. The Standard Molodensky method of datum transformation is more direct but is inexact. It also fails to reproduce the original coordinates when applied forward and back. However, this paper shows a pattern of proportionality between the misclosures and the errors in the forward approximations. This gives rise to a new method of computing the transformations, best described as "Standard Molodensky in two stages with applied misclosures" (SMITSWAM). The method is shown to be more than 1600 times more accurate than Standard Molodensky, coming close to the accuracy of the rigorous approach. SMITSWAM is also shown to be around 48% faster than the traditional form of the rigorous method which uses iteration.
Vertical deflections synthesised from the Earth Gravitational Model 2008 (EGM2008) agree with astrogeodetic vertical deflections observed over mainland Britain to within ∼1·2″ RMS (north-south) and ...∼1·4″ RMS (east-west), which is commensurate with values reported for North America, Australia and parts of continental Europe. For this assessment in Britain, there has been the additional need to transform the observed relative vertical deflections to absolute ones. Not applying horizontal datum transformations led to spurious results, so absolute vertical deflections must always be used to assess EGMs. Three datum transformations were trialled (three-parameter, seven-parameter and OSTN02), which show similar results when considering the estimated ∼0·3″ precision of these historical (1950-1976) astrogeodetic observations. Several other problems were encountered because of the historical nature of the data, comprising destruction of survey pillars, ambiguous station names and a mixture of horizontal geodetic datums available in Britain.
AbstractA method is presented to consistently tie future mean sea level rise (MSLR) scenario projections to local geodetic and tidal datums. This extends the U.S. Army Corps of Engineer (USACE) ...guidance for incorporating the effects of future MSLR into coastal projects. While USACE relies on the National Oceanic and Atmospheric Administration (NOAA) 19-year National Tidal Datum Epoch (NTDE) for its datum relationships, the approach proposed herein generalizes this guidance by choosing the appropriate 19-year epoch centered on the start year of the MSLR scenario under consideration. The procedure takes into account the local annual sea level variability, which confounds the matching to any given single year while generalizing and preserving the 19-year averaging long used by NOAA to calculate the NTDE. Examples of the MSLR scenario matching procedure are given using actual data and projections for La Jolla, California, and Sewells Point (Hampton Roads), Virginia.
Cadastral maps represent the result of the highest scale survey of any region. They are not topographic maps. Their goal is to show the property system of the mapped area, so any topographic element ...that is important for this aspect is shown while others often omitted. Historical cadastral sheets provide valuable information about not only the natural and built environment but also about some aspects of the society of the time of the survey. Because of their high scale, their creation is extremely expensive. Even the updating of the cadastre claims considerable funds from the state budgets. That is why the coordinate system, the geodetic basis of a cadastral work is rarely changed. Re-ambulation is often made on the basis of the older version, following their geodetic and topographic ‘skeleton’. The main period of the cadastral works in Europe was the first two thirds of the nineteenth century. Countries that gained their independency after this period have quite complicated cadastral systems, more or less preserving the political distribution of their lands of the time of cadastral mapping. Besides Germany, Italy provides the best example to this. Concerning Italy, the complete unification of the country was in 1870. To this time, a large part of the Apennine Peninsula was covered by cadastral surveys, mainly carried out by Piedmont, the Kingdom of Naples, and the Papal State as reported by Frazzica et al. (Geophysical Research Abstracts 11:4791,
2009
). After the WWI, territorial gains from the former Habsburg Empire resulted three new cadastral systems to be incorporated (one of them ‘lost’ after WWII). Together with them, nowadays, Italy has 31 major (“grandi origini”) and more than 800 smaller, local (“piccole origini”) cadastral systems; all of them have its own projection origin (Fig.
1
; Baiocchi et al.
2011
). At some smaller parts of the country, the modern national map grid system was later introduced and applied as reported by Moncada (
1948
), Bonifacino (
1953
), and Giucucci (Rivista del Catasto e dei Servizi Tecnici Erariali 8(2):109–113,
1953
). Fortunately, the story of the related geodetic datums was simplified prior to nowadays. Of course, the abovementioned systems had several trigonomentric networks as geodetic bases. In the first decades of the twentieth century, however, the Italian Institute of Military Geography (Istituto Geografico Militare; I.G.M) developed four geodetic networks, all on the Bessel 1841 ellipsoid; the Genova 1902 (Fig.
2
), the old Monte Mario (Fig.
3
), the Castanea delle Furie 1910, and the Guardia Vecchia (Fig.
4
) datums, for northern, central, and southern Italy and Sardinia, respectively (Mori
1922
). However, these systems were independent ones; afterward, one of them, the Genova 1902 datum, was extended to cover other parts of the country. Outside of northern Italy, the original area of this datum, the coordinates of the basepoint, and the cadastral system origins were transformed from the locally valid network to Genova 1902 datum. The present paper aims to estimate the accuracy of this extension of that system and to describe the parameters of the other systems for GIS applications, thus offering a tool for future, higher accuracy methods to fit the cadastral maps of southern Italy and Sardinia to modern grids. This can be useful also to convert some older technical maps that were referred to the same geodetic datums.
ON THE GEODETIC DATUMS IN SRI LANKA Abeyratne, P.G.V.; Featherstone, W.E.; Tantrigoda, D.A.
Survey review - Directorate of Overseas Surveys,
20/7/1/, Letnik:
42, Številka:
317
Journal Article
Recenzirano
Odprti dostop
The geodetic datums in Sri Lanka (formerly Ceylon) for latitude and longitude, height and gravity are described and discussed, because this information is not available in the open literature. It is ...recommended that most of these datums require some upgrading.
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