## Alignment of Points

This type of constraint is mostly used to horizontally or vertically
align point pairs. In general, this constraint would align points on an
imaginary line with a given direction. Note that it does not guarantee
that the order of aligned points along a given direction will be
preserved.

Alignment of points with a constant alignment direction is set up by
calling the method

```cpp
constraint_item GCE_AddAlignPoints(GCE_system gSys, geom_item p[2], double ang)
```

The function returns a descriptor of a new constraint registered in the
**gSys** system.

**p\[0\]** and **p\[1\]** pair parameters set the descriptors of the
aligned points, and the **ang** parameter is set in radians and it
determines the direction, along this direction the points would be
aligned. For example, the $ang = 0$ angular direction would correspond
to horizontal alignment of points, and if $ang = \pi/2$, then the points
would be aligned vertically.

Alignment of points with a variable alignment direction is set by the
method

```cpp
constraint_item GCE_AddAlignPoints(GCE_system gSys, geom_item p[2], geom_item dir)
```

Similar to the constant alignment direction method, this implementation
takes a constraint system **gSys** and a pair of points **p\[2\]**.

The **dir** parameter is any object registered in the solver for which
the call **GCE_GetVectorValue**(gSys, dir, GCE_DIRECTION) is valid.

Alignment will occur along the direction vector (**GCE_DIRECTION**) of
the linear object or the major axis of the ellipse.

This constraint can be used in conjunction with GCE_AddLinearDimension
to set a linear dimension as an alternative to the GCE_AddDistance
method. This method is preferable as it allows the help points of the
dimension to be better customized to suit user expectations.