These generic functions are used to determine a location on the boundary of a grid grob.

```
xDetails(x, theta)
yDetails(x, theta)
```

x

A grid grob.

theta

A numeric angle, in degrees, measured
anti-clockwise from the 3 o'clock *or* one of
the following character strings: `"north"`

,
`"east"`

, `"west"`

, `"south"`

.

A unit object.

The location on the grob boundary is determined by taking
a line from the centre of the grob at the angle `theta`

and intersecting it with the convex hull of the grob
(for the basic
grob primitives, the centre is
determined as half way between the minimum and maximum values
in x and y directions).

These functions are called in the calculation of
`"grobx"`

and `"groby"`

units as produced by
the `grobX`

and `grobY`

functions.
Methods should be written for classes derived from grob or gTree
where the boundary of the grob can be determined.