Syntax

   @ConvexHull([HANDLE_ARCS_AND_ELLIPSES])
   @ConvexHull([HANDLE_ARCS_AND_ELLIPSES, ]CONVEX)
   @ConvexHull([HANDLE_ARCS_AND_ELLIPSES, ]CONCAVE[, <alpha>])
   @ConvexHull([HANDLE_ARCS_AND_ELLIPSES, ]CONCAVE[, <alpha>], [MAKE3D|MAKE2D, <zvalue>])
   
Arguments

   <mode>   
   
      Specifies the mode of the function: if not specified, it will default to 
      CONVEX.
      
      Range: CONCAVE|CONVEX   
      
   <alpha>  
   
      The alpha value used to generate concave hulls, if not specified, optimal 
      value will be used.

      Range: Real >= 0  

   <output3D>

      Specifies if the output of coordinates are in 2D or 3D, if not specified,
      it will default to MAKE3D.

      Range: MAKE3D|MAKE2D

   <zvalue>

      The default value for z coordinates in 3D mode, when we are passing in features
      without z coordinates.

      Range: Real

      
Description

   This function replaces the geometry of the passed-in feature with a polygon 
   representing its hull. The convex hull is defined as the minimum enclosing 
   convex polygon. A convex polygon is a polygon where no interior angle is 
   greater than 180 degrees. In lay terms, the effect is similar to tightening a 
   rubber band around the feature.

   In CONCAVE mode, the concave hull, also known as the alpha hull, is 
   calculated. The concave hull may consist of multiple donuts or polygons. When 
   ALPHA is specified, it is used in the alpha hull calculation directly, a 
   larger number will generally produce more generalized results. Points or 
   features that are farther away than alpha from the rest of the geometries may 
   be culled if they do not constitute a valid area on their own. It is possible 
   that a null geometry will be returned if the specified alpha was too small 
   for the spacing of the geometry. When ALPHA is not specified, an optimal 
   alpha, which is the smallest alpha that generates a single area, will be used 
   to generate the concave hull. 
   
   If the feature was an aggregrate feature, a single hull is computed from all 
   vertices of all geometries in the aggregate. If the feature was a linear 
   feature (with more than two points), it will be turned into a polygonal 
   feature in the convex case, and in the concave hull case, input as a line. 

      Note: If the convex hull has zero area (i.e. all the original coordinates 
      are collinear), the output geometry will be a point or two-point line 
      representing the extents of the original coordinates.

   No change is made to a two-point line or point feature for the convex hull 
   case The concave hull of these features will be a null geometry.

TO BE RESOLVED

   HANDLE_ARCS_AND_ELLIPSES argument added to Syntax section above, but not 
   documented. It is currently deprecated, but kept for legacy purposes.