# Solid Section with Circle or Arcs using Tangent Intersections¶

For solid sections in circular form or with arcs a boundary or opening is described with tangent intersections. These tangent intersections are generated automatically during construction of the solid cross section in the Cross Section Editor.

The following workflow is specified here:

The boundary or the opening of the desired cross section has to be drawn at first with the AutoCAD commands. E.g. if a circular section schould be generated, a circle has to be drawn.

Then the command

`Boundary`

or`Opening`

can be called. After the definition of the necessary values in the dialog, the boundary or opening can be created by using the right mouse menu and selection of the commands`Pick lines or curves`

or`Point in area`

. With that the circle or the arcs are immediately generated and displayed. The arcs are described geometrically as polygonal points with the type tangent intersection and radii. E.g. a circle has 4 tangent intersections, one for each quarter circle.

Only the tangent intersections are then available for the definition of references.

All further cross sections elements, e.g. circular reinforcement and shear cuts, can be defined as usual.

A detailed description can be found in the chapter ‘VERT - Polygon Vertices in Absolute Coordinates’ of the manual AQUA.