Multipatch的Z值单位问题(三维坐标系和三维坐标转换，极坐标)

 

 https://desktop.arcgis.com/zh-cn/arcmap/latest/extensions/3d-analyst/multipatches.htm

为了避免Z值与X,Y值的单位存在冲突，应该将X,Y从地理坐标转到投影坐标，也就是从度分秒转为以米为单位。计算完坐标插值之后，再转为wgs84，可是z值怎么在地理坐标系和投影坐标系之间转化呢？Multipatch可以进行坐标转换吗？三维坐标投影转换参照：threejs坐标转换 三维坐标 三维坐标系(顺便复习一下极坐标和直角坐标系)

Z值如果不表明，那么在生成Multipatch的时候是默认Z为度的。。那么Z值在投影坐标系下位置是正确的。生成的Multipatch也是正确的。可是怎么把投影坐标系下生成的Multipatch转到地理坐标系中呢？

原始：（WGS84）

坐标转换：（wgs84 Web Mercator）

        //坐标转换
        private IPoint GetpProjectPoint(IPoint pPoint,bool pBool)
        {
          ISpatialReferenceFactory pSpatialReferenceEnvironemnt=new SpatialReferenceEnvironment();
          ISpatialReference pFromSpatialReference = pSpatialReferenceEnvironemnt.CreateGeographicCoordinateSystem((int)esriSRGeoCSType.esriSRGeoCS_WGS1984);//西安80 esriSRGeoCS3Type..esriSRGeoCS_Xian1980
          ISpatialReference pToSpatialReference = pSpatialReferenceEnvironemnt.CreateProjectedCoordinateSystem((int)esriSRProjCS3Type.esriSRProjCS_WGS1984WebMercatorMajorAuxSphere);//西安80 esriSRProjCS4Type.esriSRProjCS_Xian1980_3_Degree_GK_Zone_34
          if(pBool==true)//球面转平面
          {
            IGeometry pGeo=(IGeometry)pPoint;
            pGeo.SpatialReference=pFromSpatialReference;
            pGeo.Project(pToSpatialReference);
            return pPoint;
           }
           else//平面转球面
          {
            IGeometry pGeo=(IGeometry)pPoint;
            pGeo.SpatialReference=pToSpatialReference;
            pGeo.Project(pFromSpatialReference);
           return pPoint;
          }
        }

 

坐标插值：

 

转回wgs84：

 

球极坐标：https://baike.baidu.com/item/%E6%9E%81%E5%9D%90%E6%A0%87/7607962?fr=aladdin

 

三维直角坐标系和球极坐标之间的转换关系：

球面上的所有点，默认都是高程为0。而假设高程不为0，那么，就出现了另一个半径为ρ+h的新球，

那么，不同的高程就有无数个球，那么对于三维来说最好的坐标系其实是直角坐标系。因为无论是地理坐标系，还是投影坐标系，似乎参考椭球都是唯一的。

 

 Z值的坐标系和单位怎么设置(垂直坐标系：Vertical Coordinate System)

A vertical coordinate system defines the origin for height or depth values. Like a horizontal coordinate system, most of the information in a vertical coordinate system is not needed unless you want to display or combine a dataset with other data that uses a different vertical coordinate system.

     Perhaps the most important part of a vertical coordinate system is its unit of measure. The unit of measure is always linear (e.g., international feet or meters). Another important part is whether the z values represent heights (elevations) or depths. For each type, the z-axis direction is positive "up" or "down", respectively.

     One z value is shown for the height-based mean sea level system. Any point that falls below the mean sea level line but is referenced to it will have a negative z value. The mean low water system has two z values associated with it. Because the mean low water system is depth-based, the z values are positive. Any point that falls above the mean low water line but is referenced to it will have a negative z value.

 

 https://desktop.arcgis.com/zh-cn/arcmap/10.6/map/projections/fundamentals-of-vertical-coordinate-systems.htm

不知为何，Z值只有在墨卡托投影下才能正常显示。。。