Coordinate reference systems and projections（坐标参考系与投影）¶
Geospatial data can be stored in various reference systems and projections ↗. Different projections can make it easier or harder to handle human-input numbers or perform area/length calculations. All 2D map projections distort real-world data by flattening the Earth, which is a 3D ellipsoid, to a screen/paper, which is a 2D surface. These distortions can occur in shape, area, distance, and direction (together known as SADD).
A library of all standard projections is available in the European Petroleum Survery Group (EPSG) public registry ↗. The most common projection is “standard” latitude and longitude (WGS 84 aka EPSG:4326 ↗). However, source data often comes in a different projection, based on local conditions and norms. For example, many US-based customers use data captured using the North American Datum 1983 (NAD83), which has a different underlying model of the Earth’s surface than the one used by WGS 84.
It is important to understand the coordinate reference system (CRS) that your data uses, particularly if you are working with other data stored in a different CRS. If you have data from the same location which are stored in different coordinate reference systems, these data will not line up on your map. You should always consult key stakeholders and subject matter experts to clarify important questions related to CRS, data accuracy, and other best practices.
All maps in Foundry expect WGS 84 and use the Web Mercator Projection ↗.
Learn more about manipulating CRS in PySpark transforms.
中文翻译¶
坐标参考系与投影¶
地理空间数据可以存储在不同的参考系和投影（reference systems and projections）中。不同的投影会影响人工输入数字的处理难度，以及面积/长度计算的便捷性。所有二维地图投影都会将地球（三维椭球体）展平到屏幕或纸张（二维表面）上，从而对现实世界数据产生扭曲。这些扭曲可能发生在形状（shape）、面积（area）、距离（distance）和方向（direction）上（统称为SADD）。
欧洲石油调查组织（EPSG）的公共注册中心（public registry）提供了所有标准投影的库。最常见的投影是"标准"经纬度（WGS 84，即EPSG:4326）。然而，源数据通常基于当地条件和规范采用不同的投影。例如，许多美国客户使用基于北美基准面1983（NAD83）采集的数据，该基准面对地球表面的底层模型与WGS 84所使用的模型不同。
理解数据所使用的坐标参考系（CRS，coordinate reference system）至关重要，尤其是在处理以不同CRS存储的其他数据时。如果同一位置的数据存储在不同的坐标参考系中，这些数据将无法在地图上对齐。您应始终咨询关键利益相关者和领域专家，以澄清与CRS、数据准确性及其他最佳实践相关的重要问题。
Foundry中的所有地图均采用WGS 84，并使用Web墨卡托投影（Web Mercator Projection）。
了解更多关于在PySpark转换中操作CRS（manipulating CRS）的信息。