AsTextZM (geometry Data Type)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
SQL database in Microsoft Fabric
Returns the Open Geospatial Consortium (OGC) Well-Known Text (WKT) representation of a geometry instance augmented with any Z (elevation) and M (measure) values carried by the instance.
Syntax
.AsTextZM ()
Return Types
SQL Server return type: nvarchar(max)
CLR return type: SqlChars
Remarks
Examples
The following example creates a Point instance that contains Z (elevation) and M (measure) values. STAsText() selects the WKT values, (1 2); AsTextZM() selects the same WKT values and also returns the values for Z and M, yielding (1 2 3 4).
DECLARE @g geometry;
SET @g = geometry::STGeomFromText('POINT(1 2 3 4)', 0);
SELECT @g.STAsText();
SELECT @g.AsTextZM();