This attribute controls the appearance of an annotated
coordinate grid (drawn with the AST_GRID routine) by determining
the logarithmic interval between the "major" axis values of a Plot, at
which (for example) major tick marks are drawn. It takes a separate
value for each physical axis of the Plot so that, for instance,
the setting "LogGap(2)=100.0" specifies the ratio between adjacent major
values along the second axis. The LogGap attribute is only used when
the LogTicks attribute indicates that the spacing between major axis
values is to be logarithmic. If major axis values are linearly spaced
then the gap is specified using attribute Gap.
The LogGap value supplied will be rounded to the nearest power of 10.
The reciprocal of the supplied value may be used if this is necessary
to produce usable major axis values. If a zero or negative value is
supplied, an error will be reported when the grid is drawn. The default
behaviour is for the Plot to generate its own LogGap value when
required, based on the range of axis values to be represented.