摘要:

AbstractThe paper presents the results obtained from an experimental investigation into the optimisation of the three-dimensional digital elevation data compression procedure [1]. Three statistical criteria for testing data points were examined, using photogrammetrically sampled and cartographically digitised digital elevation data. The areas tested presented a considerable variation in topography. The photogrammetrically sampled area contains both steep sloping and generally flat terrain types, while the cartographically digitised one contains a hilly undulating terrain. The findings showed that optimum results from the procedure can only be obtained by optimum combination of the statistical criterion, the terrain characteristics and the data compression level required.

ISSN:0039-6265    

DOI:10.1179/sre.1992.31.243.248

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA geodetic levelling network was established in the main campus of the Ahmadu Bello University, Zaria, in 1976. This network, which initially consisted of 17 lines and 10 junction points with a total length of 11 km, was extended in 1979 by the addition of new bench marks bringing the total length of levelling to 18 km. A recovery levelling to replace lost bench marks and further extend the net was carried out in 1983, resulting in a total length of levelling of 27 km, made up of 21 links and 11 junction points. Repeated levelling carried out in 1979, 1980, 1983 and 1990 shows that no significant movement had occurred at the marks. By 1983 the apparent vertical movement of any of the bench marks sited in 1976 was less than 1 mm. For the bench marks established in 1978 the apparent movement was less than 5 mm in the first year after emplacement, and less than 1 mm by 1983.

ISSN:0039-6265    

DOI:10.1179/sre.1992.31.243.263

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA new approach to the optimal Second Order Design of geodetic networks with respect to criterion matrices has been developed. By equating the variance-covariance matrix of the estimated coordinates with the given criterion matrix, one obtains generally a system of redundant nonlinear and inconsistent equations to be solved for unknown weights. This system is then linearised using Taylor series. An optimal solution for observational weights is sought by best approximating the given criterion matrix itself, rather than its inverse, in the sense of least squares. A numerical example is given to illustrate its application.

ISSN:0039-6265    

DOI:10.1179/sre.1992.31.243.279

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe atmosphere has three main effects on radio-wave propagation. It causes attenuation, time delay and angular bending. The accuracy of space-to-earth distance measurements is therefore often limited by how well the neutral atmosphere can be modelled. The time-delay translated into equivalent excess propagation path or path delay can be separated into two parts, the hydrostatic delay and the wet delay. In this report new models for the estimation of the hydrostatic delay are extensively tested and compared with four other well-known models. For the elevation dependence of the hydrostatic delay we base our analysis on a simple continuous fraction form. We present models with global and c1imatedependent parameters.

ISSN:0039-6265    

DOI:10.1179/sre.1992.31.243.289

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0039-6265    

DOI:10.1179/sre.1992.31.243.299

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0039-6265    

DOI:10.1179/sre.1992.31.243.301

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0039-6265    

DOI:10.1179/sre.1992.31.243.302

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0039-6265    

DOI:10.1179/sre.1992.31.243.303

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0039-6265    

DOI:10.1179/sre.1992.31.243.304

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0039-6265    

DOI:10.1179/sre.1992.31.243.305

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor