ArcGIS Unknown Spatial Reference问题的讨论

shp文件在Arcgis打开后经常因为原有坐标系无法识别而丢失信息，出现以下提示信息： Unknown Spatial Reference The following data sources you added are missing spatial reference information. This data can be drawn in ArcMap, but cannot be project
shp文件在Arcgis打开后经常因为原有坐标系无法识别而丢失信息，出现以下提示信息：
"Unknown Spatial Reference
The following data sources you added are missing spatial reference information. This data can be drawn in ArcMap, but cannot be projected."
今天偶然见终于找到了解决方法。先给出ESRI Supporter Center关于这个问题给出的解决方法：
Error: Unknown Spatial Reference Article ID: 31999
Software: ArcGIS - ArcEditor 9.0, 9.1, 9.2 ArcGIS - ArcInfo 9.0, 9.1, 9.2 ArcGIS - ArcView 9.0, 9.1, 9.2
Platforms: N/A
Error Message
Adding data to ArcMap which does not have the coordinate system or projection defined displays the following error message:
"Unknown Spatial Reference
The following data sources you added are missing spatial reference information. This data can be drawn in ArcMap, but cannot be projected."
Cause
The data does not have a coordinate system or projection defined.
This message is returned for all data types which can be added to ArcMap including geodatabase feature classes, shapefiles, coverages and CAD data, as well as supported raster or image formats which do not have a coordinate system definition.
Solution or Workaround
Identify and define the coordinate system for the data, using the Define Projection Tool in ArcToolBox > Data Management Tools > Projections and Transformations or the data's property page in ArcCatalog.
其实这个解决方案是对的，以前也按照这个方法试过，但是没有成功，关键点在这里：
ArcToolBox > Data Management Tools > Projections and Transformations > Define Projection，这里要给文件加入的坐标系统应当是地理坐标系统（Geographyical Coordinate System），下一步再将投影转换到你所要的投影系统下。
我觉得之前失败原因在这里：因为软件无法识别空间参考信息，所以要先定义椭球体（定义地理坐标系，相当于去掉原有的投影），然后再投影（Projection）。之前我们总想一步到位，软件本来就不识别文件的投影信息，你让它转换到另一个投影下，自然有点难为它了。关于地理坐标系和投影坐标系的区别就不再赘述了。