## Collinearity

Collinearity means that the geometric objects included in this
constraint lie on the same line. Collinearity can be defined both for
two geometrical objects, and for three points.

Collinearity constraint is created for a pair of geometric objects by
calling the

```cpp
constraint_item GCE_AddColinear(GCE_system gSys, geom_item g[2])   
```

it requires that one of the constraint arguments should be a
straight-line, and the other one should be either a line or a point. The
geometric arguments are set by the **g**\[2\] pair. The function returns
a descriptor of a new constraint registered in the **gSys** system.

Collinearity constraint can be created for three points by calling the

```cpp
constraint_item GCE_AddColinear3Points(GCE_system gSys, geom_item p[3])
```

The descriptors of three points that should be placed on one line are
passed via the **p**\[3\] parameter. The function returns a descriptor
of a new constraint registered in the **gSys** system.