There are forms that are difficult, impossible or very tedious to define as we need to know the coordinates of all the fixed points. Forms that are supported on arches are the typical case of those .

For these activities, WinTess3 provides a tool which is called Auxiliary (points, lines,…). Using Auxiliary, we draw objects that are in the same 3D space of tensile structure but do not belong to the structure. The program draws them in orange color. The benefits of these auxiliary objects are very wide and depend on the user to be able to get the maximum benefit  from it. In another section, we will discuss how to create auxiliary.

We are going to make a very simple example. We start with a rectangular grid of 10×5 sections. In the central short axis, we create a transverse auxiliary arch of five segments.
Using the menu Nodes | Move nodes click on a knot just under the arch and move it to the corresponding node of the arc.
We do the same with the other nodes.
We fix the end points of the arc.
We press the Start button () to find the new form.
If we generate the elements we have a more complete picture of the membrane.