How can I flatten a 3D Line String to 2D in elevation
This can be done using the 'Flatten Curve' tool, which will flatten or project a curve-type element, such as a line string, complex chain, complex shape or B-spline curve, into a specified plane.
From the Ribbon select the 'Flatten Curve' tool ( Drawing > Curves > Curve Utilities )
In the Tool Settings dialog select the plane required for your elements
Select the element to flatten ( Unless already selected in step 1 ) and accept by placing a datapoint anywhere in the view
Help Documentation:> Home > Working with Existing Elements > Changing Elements > Updating Elements from a Template > Modify Curves Toolbox > Flatten Curvehttps://docs.bentley.com/LiveContent/content/en/MicroStation%20Help-v10/ModifyCurvesFlattenCurve