WKT是什么?关于坐标系统的.

Question

WKT是什么?关于坐标系统的.

Answer 1

Well-Known Text (WKT) Representation of Spatial Reference Systems：顾名思义用众所周知的文字形式来描述看见坐标参照系统,它与EPSG（2005年已经换名）的坐标文字表述模型一致.
基础知识：坐标参照系有三种最常见的子类：地心坐标系(geocentric cs、GEOCCS),地理坐标系(geographic cs、GEOGCS),和投影坐标系(projected cs、PROJCS)以及相互之间的关系,可以参考《坐标系、坐标参照系、坐标变换、投影变换》.投影参数内容：Ellipsoid 、 Datum ；Projection,可以参考《地图投影为什么》.
坐标系的文字描述的扩展BN范式(EBNF)定义如下：
= | |
= PROJECTION[""]
= PARAMETER["",]
=
= DATUM["",]
= SPHEROID["",,]
= NOTE:semi-major axis is measured in meters and must be > 0.
=
= PRIMEM["",]
=
=
=
= UNIT["",]
=
以下示例说明,参照上述参数,然后比瓢画葫芦即可自行用WKT创建坐标系.
地理坐标系的格式：= GEOGCS["",,,]
WGS1984的地理坐标系WKT形式：
GEOGCS["WGS 84",
DATUM["WGS_1984",
SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],
AUTHORITY["EPSG","6326"]],
PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],
UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],
AUTHORITY["EPSG","4326"]]
投影坐标系的格式：= PROJCS["",,,{,}* ]
WGS1984地理坐标,统一横轴墨卡托(UTM)投影,中央经线117E的投影坐标系WKT形式：
PROJCS["WGS 84 / UTM zone 50N",
GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]],
PROJECTION["Transverse_Mercator"],
PARAMETER["latitude_of_origin",0],
PARAMETER["central_meridian",117],
PARAMETER["scale_factor",0.9996],
PARAMETER["false_easting",500000],
PARAMETER["false_northing",0],
UNIT["metre",1,AUTHORITY["EPSG","9001"]],
AUTHORITY["EPSG","32650"]]
地心坐标系格式相似于地理坐标系：= GEOCCS["",,,]
参数中出现AUTHORITY是EPSG的玩意,在自定义坐标系时可以忽略,我会在后面详细介绍EPSG相关内容.WKT更具体的可参考OGC相关文档：如SFA、《SF for OLE/COM》等.
练习：给出下属投影坐标系参数,请用WKT方式表述.
投影参数：椭球体,Krasovsky_1940；基准面,北京1954；投影：兰勃特双标准纬线,25N,47N；中央经线,117E.
参考答案：
PROJCS["liongg",
GEOGCS["GCS_Beijing_1954",
DATUM["D_Beijing_1954",SPHEROID["Krasovsky_1940",6378245.0,298.3]],
PRIMEM["Greenwich",0.0],
UNIT["Degree",0.0174532925199433]],
PROJECTION["Lambert_Conformal_Conic"],
PARAMETER["False_Easting",20500000.0],
PARAMETER["False_Northing",0.0],
PARAMETER["Central_Meridian",0.0],
PARAMETER["Standard_Parallel_1",25.0],
PARAMETER["Standard_Parallel_2",47.0],
PARAMETER["Scale_Factor",1.0],
PARAMETER["Latitude_Of_Origin",0.0],
UNIT["Meter",1.0]]
有个偷懒的方法就是用商业软件譬如ArcGIS按照参数新建投影,然后在.prj文件中提取投影内容并修改.