## Directed Distance Dimension

A simple distance dimension measures a distance between points lying on
geometric objects. A directed distance dimension is also defined for a
pair of points, but the distance is measured between the projections of
points along the line having a particular direction. This dimension type
is mostly used to create vertical and horizontal dimensions that define
the distance between points projected on X or Y axis. Fig. 1 shows the
examples of vertical and horizontal dimensions for a point pair.
Generally, the dimension direction can be arbitrary.

![image](../../pictures/S.2.5.1.png){width="50%"}

Fig. 1

Directed dimensions also behave in a specific way during a geometric
transformation of the sketch by the
[GCE_Transform](../../../CALCULATION_OF_TWO-DIMENSIONAL_CONSTRAINTS/subsections/EN/Geometric_Transformation.md)()
method. Directed dimension would rotate if the transformation matrix
contains a rotation component.

Directed dimensions are created by the

```cpp
{ll}
constraint_item GCE_AddDirectedDistance(GCE_system gSys, geom_item p[2]
                                     , const GCE_ldim_pars & dPars)
```

The function returns the descriptor of directed dimension.

The method input parameters are:

-   **gSys** is a parametric sketch constraint system;

-   **p**\[2\] are the descriptors of point pair;

-   **dPars** is a data structure, that besides standard settings
    inherent to distance dimensions (see similar settings for
    **GCE_AddDistance**()), additionally sets the **dPars.dirAngle**
    angular direction. For instance, if it is required to define a
    *horizontal* dimension, then **dPars.dirAngle** = $0$; if it is
    required to define a *vertical* dimension, then **dPars.dirAngle** =
    $\pi$/2. Generally, **dPars.dirAngle** can range from $0$ to $2\pi$.

**Note.** In the current C3D Solver version, the directed dimension can
be set only for points.