By Geoffrey H. Dutton
Whilst spatial information is digitized to be used in geographic info structures and different software program, information regarding its unique scale, solution and accuracy is usually misplaced. hence, utilizing such info at assorted scales and mixing it with info from different assets can be tricky. Mapping vector facts at smaller than the unique scale calls for its generalization, that is frequently dealt with through post-processing in ways in which are just weakly supported by means of databases. The versions and strategies defined during this booklet triumph over many such difficulties by means of supplying a multi-resolution info illustration that enables retrieval of map facts at a hierarchy of scales, in addition to documenting the accuracy of each spatial coordinate.
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Additional resources for A Hierarchical Coordinate System for Geoprocessing and Cartography (Lecture Notes in Earth Sciences)
Attributes and metadata for the resultant layer can indicate what sources formed it, and carry over descriptions of their quality, but they cannot easily indicate which portions of particular features came from what source. Therefore, should the positional accuracies of two inputs to an overlay operation differ, the accuracy of the result will vary spatially in uncertain, uncontrolled and undocumented ways. 4 illustrates one basis for this pervasive problem. a. Land Use Polygons o positional error b.
The scheme, called DEPTH (for Delta-Encoded Polynomial Terrain Hierarchy) was based on the assumption that grid samplings of continuous surfaces such as terrain have vertical accuracies that are constrained by their horizontal sampling resolution; the larger an area covered by a grid cell, the less certainty there can be that a single elevation value characterizes it within a specified error bound (Dutton and Chan 1983). From a grid, a pyramidal quadtree data structure was created coding each data element with 2 bits, indicating whether the elevations of children of a quadrant moved up, moved down or stayed the same level as their parent.
The triangular subdivisions of octants are identified by adding a quaternary digit (0, 1, 2 or 3) to a series of them built up in the course of fixing a location. Upon reaching a point's limit of precision the process stops, and the sequence of digits becomes the QTM address (a quadtree leaf node which we denote as QTM ID) of that point. Address digits are assigned to quadrants according to a method that always numbers the central one 0, but permutes the other three identifiers at each level. 3 Strictly speaking, the single-node-occupancy restriction is only enforced on a perobject basis.