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@Section
@Title { Placing arbitrary objects on the graph }
@Tag { arbobj }
@Begin
@PP
As we have just seen, the repertoire of symbols that @Code "@Data" is
able to place on the graph is quite limited. However, there is a way
to place any number of arbitrary Lout objects anywhere on the graph,
using the @Code objects option to the @Code "@Graph" symbol:
@ID @OneRow @Code {
"@Graph"
" objects {"
" @CTR at {2.5 6.0} @Eq { y = x sup 2 }"
" @CTR at {4.5 7.0} @Eq { y = x sup 3 }"
" }"
}
where we have used the @Code "@Eq" symbol from Chapter {@NumberOf equations}
twice to place two equations onto the graph at the points {@Code "2.5 6.0"}
and {@Code "4.5 7.0"} respectively. An example result appears in the next
section.
@PP
In addition to {@Code "@CTR"}, there are eight other symbols which may
be used within the @Code "objects" option in the same way: {@Code "@NW"},
{@Code "@SW"}, {@Code "@SE"}, {@Code "@NE"}, {@Code "@N"}, {@Code "@W"},
{@Code "@S"}, and {@Code "@E"}. These place the object just to the
northwest of the point, to the southwest, and so on instead of centring
it over the point. By `to the northwest' we mean that the object's bottom
right corner coincides with the point, and similarly for the other symbols.
@PP
Each of these symbols has a @Code "margin" option which enlarges the
object by adding a margin around it before placing it:
@ID @Code "@NW at {2.5 6.0} margin { 0.3 ft } @Eq { y = x sup 2 }"
shows the default value, 0.3 times the current font size. As the margin
is increased, the object moves further away from the point.
@PP
The major advantage of the @Code "objects" option over the @Code "@Data"
symbol is that arbitrary Lout objects may be used. The @Code "@Data"
symbol however is able to place many copies of its symbols onto the graph,
and also allow for them when connecting points together with lines. Also,
the points within the @Code "objects" option are not taken into account
when deciding on the permissible range of x and y values, whereas the
points within the @Code "@Data" symbol are. Altogether it seems best
to use the @Code "@Data" symbol for the bulk of the data points, and to
use the @Code "objects" option for adding a small number of labels or
other decorations.
@PP
The @Code "objects" option may contain @Code "@Graph" symbols, but in
that case, owing to a deficiency in the implementation, those symbols
will need to have their @Code save options (Section {@NumberOf grerrors})
set to {@Code yes}.
@End @Section
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