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Geology topics

Jan W. van Roessel

Publications and source records attributed to Jan W. van Roessel.

8 recordsLinked to original sources
USGS2013

An algorithm for locating candidate labeling boxes within a polygon

Vector-based geographic information systems usually require annotation, such as a polygon number or attribute data, in a suitable location within a polygon. Traditional methods usually compute the polygon centroid, test the centroid for inclusion or exclusion, and select some alternative point when the centroid falls outside the polygon. Two problems are associated with this approach: (1) the text can be centered on the point, but may be placed in a visually awkward place, and (2) part of the text may fall outside the polygon and may overlap other polygon boundaries or other text labels. An algorithm is presented that circumvents both of these problems, by computing a number of horizontal candidate labeling rectangles (boxes) within a polygon from which a suitable selection can be made or from which one may conclude that the text label does not fit the polygon.

American Cartographer↗
USGS2013

A new approach to plane-sweep overlay: topological structuring and line-segment classification

An integrated approach to spatial overlay was developed with the objective of creating a single function that can perform most of the tasks now assigned to discrete functions in current systems. Two important components of this system are a unique method for topological structuring, and a method for attribute propagation and line-segment classification. -Author

Cartography and Geographic Information Systems↗
USGS1988

Conversion of Cartesian coordinates from and to Generalized Balanced Ternary addresses

Hexagonal grids have several advantages over square grids, such as a greater angular resolution and unambiguous connectivity. The Generalized Balanced Ternary (GBT) system is a spatial addressing method for hexagonal grids in which the hexagons are arranged in hierarchical aggregates, and which accommodates vector operations in GBT space. Efficient algorithms for converting Cartesian coordinates from and to GBT addresses are based on the dual representation of the hexagonal tessellation. The GBT-to-Cartesian algorithm is an order of magnitude faster than the Cartesian-to-GBT algorithm, the latter requiring interpolation and GBT addition for each digit of the generated GBT address.

Photogrammetric Engineering and Remote Sensing↗
USGS1987

Design of a spatial data structure using the relational normal forms

In previous work, a relational data structure aimed at the exchange of spatial data between systems was developed. As this data structure was relational it was of first normal form, but compliance with the higher normal forms was not investigated. Recently, a new procedural method for composing fully normalized data structures from the basic data fields has been developed by H. C. Smith, as an alternative to the process of non-loss decomposition which is difficult to understand. Smith's method has been applied to data fields required to store points, lines and polygons in a chain-node spatial data model. When geographic domain, coverage layer and map are also considered, the procedure naturally leads to a catalogue model, needed for the exchange of spatial data. Although the method produces a fully normalized data structure, it is not as easy to identify which normal forms are responsible for the ultimate arrangement of the data fields into relations, but the benefits of these criteria for data base development also apply to spatial data structures and related ancillary data.

International Journal of Geographical Information ↗
USGS1987

An algorithm for locating candidate labelling boxes within a polygon

Vector-based geographic information systems usually require annotation, such as a polygon number or attribute data, in a suitable location within a polygon. Traditional methods usually compute the polygon centroid, test the centroid for inclusion or exclusion, and select some alternative point when the centroid falls outside the polygon. Two problems are associated with this approach: (1) the text can be centered on the point, but may be placed in a visually awkward place, and (2) part of the text may fall outside the polygon and may overlap other polygon boundaries or other text labels. An algorithm is presented that circumvents both of these problems, by computing a number of horizontal candidate labelling rectangles (boxes) within a polygon from which a suitable selection can be made or from which one may conclude that the text label does not fit the polygon.

Conference Paper↗
USGS1986

Vector data structure conversion at the EROS Data Center

With the increasing prevalence of GIS systems and the processing of spatial data, conversion of data from one system to another has become a more serious problem. This report describes the approach taken to arrive at a solution at the EROS Data Center. The report consists of a main section and a number of appendices. The methodology is described in the main section, while the appendices have system specific descriptions. The overall approach is based on a central conversion hub consisting of a relational database manager and associated tools, with a standard data structure for the transfer of spatial data. This approach is the best compromise between the two goals of reducing the overall interfacing effort and producing efficient system interfaces, while the tools can be used to arrive at a progression of interface sophistication ranging from toolbench to smooth flow. The appendices provide detailed information on a number of spatial data handling systems and data structures and existing interfaces as well as interfaces developed with the described methodology.

Open-File Report↗
USGS1985

A relational approach to vector data structure conversion

The proliferation of geographic information systems and digital data bases is creating a need for efficient methods to convert data from one spatial data structure to another. One approach is to create ad hoc interfaces, with a potential of N(N-1) interfaces for N data structures. Using an intermediate data structure, at most 2N interfaces are required. An intermediate relational data structure is therefore proposed that takes the form of a set of normalized relations stored in a relational information management system. The advantages of this approach are found in the simplicity of the relational approach, and the availability of relational operators to be used as higher level tools, to convert from and to the relational data structure. The Relational Information Management System (RIM) is used for the ongoing research. In conjunction with the relational data structure, another higher level tool has been developed to cope with linked lists, tree structures, vectors, and matrices, which are not otherwise easily reduced. This data tracking system is programmable at a higher level, in a syntax that allows a concise expression of the desired restructuring. Output from this system can be further operated on by relational operators to arrive at the desired intermediate data structure. This, and other topology verification and checking tools, are visualized as part of a core system dedicated to the conversion and collation of spatial data from diverse origins.

Conference Paper↗