GeomFromGml (geometry Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Construct a geometry instance given a representation in the SQL Server subset of the Geography Markup Language (GML).
For more information on the Geography Markup Language, see the following Open Geospatial Consortium Specifications:
OGC Specifications, Geography Markup Language
Syntax
GeomFromGml ( GML_input, SRID )
Arguments
GML_input
Is an XML input from which the GML will return a value.
SRID
Is an int expression representing the spatial reference ID (SRID) of the geometry instance you wish to return.
Return Types
SQL Server return type: geometry
CLR return type: SqlGeometry
Remarks
This method will throw a FormatException if the input is not well-formatted.
Examples
The following example uses GeomFromGml() to create a geometry instance.
DECLARE @g geometry;
DECLARE @x xml;
SET @x = '<LineString xmlns="http://www.opengis.net/gml"> <posList>100 100 20 180 180 180</posList> </LineString>';
SET @g = geometry::GeomFromGml(@x, 0);
SELECT @g.ToString();