SQL Anywhere supports both flat-Earth and round-Earth representations. Flat-Earth reference systems project all or a portion of the surface of the Earth to a flat, two dimensional plane (planar), and use a simple 2D Euclidean geometry. Lines between points are straight (except for circularstrings), and geometries cannot wrap over the edge (cross the dateline).
Round-Earth spatial reference systems use an ellipsoid to represent the Earth. Points are mapped to the ellipsoid for computations, all lines follow the shortest path and arc toward the pole, and geometries can cross the date line.
Both flat-Earth and round-Earth representations have their limitations. There is not a single ideal map projection that best represents all features of the Earth, and depending on the location of an object on the Earth, distortions may affect its area, shape, distance, or direction.
Discuter à propos de cette page dans DocCommentXchange.
|Copyright © 2013, SAP AG ou société affiliée SAP - SAP Sybase SQL Anywhere 16.0|