ABSTRACTS

SaLIS vol. 64, no. 3

2004

 

Assessment of the New National Geoid Height Model—GEOID03

Daniel R. Roman, Yan Ming Wang, William Henning, and John Hamilton

 

The GEOID03 model was developed in the same manner as GEOID99 using an underlying gravimetric geoid, USGG2003, and updated GPS ellipsoidal heights on leveled benchmarks (GPSBMs). USGG2003 is similar to G99SSS, however, it includes an updated model for gravity anomalies in the deep ocean areas, GSFC00.1. The conversion surface for GEOID03 was developed from 14,185 GPSBMs at a 5 arc-minute grid interval, which provided a substantial increase in the spatial coverage and reduced errors due to interpolation. The fit to these same points afterwards was 4.8 cm (2), which was comprised of both correlated (attributable to GEOID03) and uncorrelated (GPS observation error) signals. The uncorrelated signal was 4.2 cm (2) and the correlated signal was 2.0 cm (2), with a 3.5 km correlation wavelength. GEOID03 thus had a very good fit with the GPSBMs, and can be relied upon to convert between the NAD 83 and NAVD 88 datums to the centimeter level.

 

Precision of Points Computed from Intersections of Lines or Planes

Peter Cederholm

 

Not all points are directly accessible when doing detail surveys with GPS. This paper suggests a method for estimating these points. The points are computed from intersections of lines that are surveyed with GPS. The lines are computed by least squares estimation. Further, the suggested method estimates the precision of the points. When using laser scanning a similar problem appears. A laser scanner captures a 3-D point cloud, not the points of real interest. The suggested method can be used to compute three-dimensional coordinates of the intersection of three planes estimated from the point cloud. The method can also be used to predict the precision of the points prior to a survey. An example is given.

 

Log-linear Model for Discrete Anisotropic Dynamics of Geographical Objects

Efim Kelman, Michael Sonis, and Maxim Shoshany

 

Discrete dynamic GIS models have become the key research directions of the 21st century (Bergougnoux 2000).  A new log-linear model has been introduced for describing the dynamics of boundary lines. Boundaries of geographical objects frequently exhibit anisotropic behavior, with the magnitude of their dynamics varying in time and space. The new model’s dynamic behavior is particularly useful for modeling anisotropic spatial dynamics of two and three-dimensional objects in geographical databases. This study describes the model and illustrates its characteristic using simulation examples. 

Keywords: GIS, discrete dynamics, bifurcations, simulation, boundary line dynamics, anisotropic

 

The 3-Point Resection Problem in Photogrammetry

Willie Tan

This paper provides a simple solution to the three-point resection problem in photogrammetry. It is based on Grunert’s (1841) closed form solution but uses the Newton-Raphson iteration procedure, and its desirable property of quadratic convergence, to solve the quartic equation. The proposed solution is superior to closed-form solutions with multiple roots. Although four-point closed form formulas also exist to define a unique solution, they are quite complex.

 

 

A Geodetic Approach: Universal No-Projection Seamless Mapping

Muneendra Kumar

 

The Universal No-Projection Seamless Mapping (UNSM) system is based on a bird’s-eye-view of the Earth’s surface in small-size ellipsoidal trapezoids. At the poles, the smaller side of the trapezoid will be zero and it will become triangular. Each trapezoid is mapped individually and independently of the adjoining neighbor. The smaller the area size, the flatter will be the trapezoid, which on paper will become a trapezium. Keeping the trapezium sides equal to the actual lengths of the latitudinal or longitudinal arcs of the corresponding trapezoid, distortions due to flattening of the bulge will be practically negligible for topographic maps, charts, and cadastral plats. The trapeziums or triangles are not converted to squares or rectangles, and maps will have true North and scale with no discontinuity in coordinates. The Earth’s ellipsoidal surface is mapped as a mosaic producing seamless flat maps and charts.

 

 

Modelling the Optimum Routes for Linking Potential Reservoir Sites to Demand Areas

in Mountainous Tropical Islands

Serwan M. J. Baban, Kamruzaman Wan Yusof, Ian D. L. Foster, Bheshem Ramlal

 

Identifying efficient pathways for linking potential reservoir sites to demand areas can be a difficult task in mountainous tropical regions. Options for locating optimum water pipe routes to link two proposed reservoir sites to future demand areas in the Langkawi Island, Malaysia, were developed and simulated. A basic water pipe locating criteria was developed based on land use, terrain, geological, and environmental factors. A raster based GIS, IDRISI was used to geographically associate this information with individual land use/cover types on the island. Then, a friction surface cost-value and a friction surface were created. Subsequently, two alternative scenarios were established and implemented. The results from both scenarios show that the paths will pass through the lowest friction surface value, i.e., grassland and mixed horticulture. The results from both scenarios were evaluated against straight-line paths. The analysis shows that a straight-line path may not necessarily be the cheapest distance in mountainous tropical environments. This study has demonstrated the advantages of using GIS in developing and simulating different options for finding optimum paths and providing reliable management options for decision makers.

Keywords:  Modelling, optimum routes, reservoirs, GIS, Malaysia

 

Removal as a Legal Remedy for Relief against Encroachments

Thomas McDermott

 

This paper discusses the nature of encroachments on real property, and how encroachment disputes are resolved in the courts. The central question found in most encroachment disputes is asked: In what situations should the legal remedy for relief against an encroachment be the removal of the encroachment itself. Because of the limitless variety of encroachment scenarios involving trees, fences, and party walls, the discussions in this paper is limited to encroachments of a more “permanent” nature. Other boundary topics such as adverse possession, boundary by agreement, and estoppel are addressed as well.

 

The Arc of the 30th Meridian

J. R. Smith

 

Geodesists and their predecessors have been measuring meridian arcs for over 2000 years. Of the numerous arcs measured in that time some have had particular significance. On June 8th, 2004, at Buffelsfontein outside Port Elizabeth in South Africa, a plaque was unveiled on what appeared to be no more than a standard geodetic survey pillar. Yet, this point has particular significance as it is the southernmost station of the Arc of the 30th Meridian through East Africa. The plaque commemorates the 125th anniversary of when the Arc was first thought of and the 50th of when it was completed.