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Tissot's Indicatrix and regular grids have been used for assessing map projection accuracies. Despite their broad applicability for accuracy assessment, they have limitations in quantifying resampling errors caused by map projections. This is due to the structural uncertainty with regard to the placement and pattern of grids. It is also difficult to calculate the absolute amount of resampling error in each projection. As an alternative to traditional testing methods, the use of random points was investigated. Specifically, random point generation, resampling with spherical block search algorithms, resampling accuracy with a perfect grid, and resampling accuracy with eight projections were investigated and are discussed here. Eight global referencing methods were tested: the equal-area cylindrical, sinusoidal, Mollweide, Eckert IV, Hammer-Aitoff, interrupted Goode homolosine, integerized sinusoidal projections, and the equal area global gridding with a fixed latitudinal metric distance. The resampling accuracy with a perfect grid is about 75 percent. Results showed the sinusoidal and the integerized sinusoidal projections and equal-area global gridding to achieve the highest accuracies. 相似文献
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《制图学和地理信息科学》2013,40(2):129-138
We examine some benefits of using the medial axis as a centerline for rivers and lakes. One benefit, automatic centerline generation, has been used for many years. We show that additional benefits can be derived from the geometric relationships between the medial axis and the riverbanks or lakeshores. These include area estimates, association of centerline analysis to banks, and definition of opposite for riverbanks. We also report on our experience at approximating the medial axis with a Voronoi diagram of point sites. 相似文献
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《制图学和地理信息科学》2013,40(5):300-302
The Spatial Data Transfer Standard (SDTS) was designed to transfer both vector and raster data sets. In the early development of the SDTS, the designers recognized that there was a need to transfer raster data in addition to the more challenging vector data. As a result, the SDTS includes a “raster module” that accommodates a variety of raster data structures and formats. A raster profile is being developed that will exercise a selected subset of SDTS capabilities in order to provide a simple-to-use transfer of complete raster data sets. 相似文献
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《制图学和地理信息科学》2013,40(4):345-351
This paper describes two mapping algorithms for plotting the templates needed to construct three dimensional landform relief models. A contour relief model and a profile relief model were assembled using the elevation data extracted from Defense Mapping Agency 1:250,000 scale Digital Terrain Tapes. 相似文献
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