Creating overlays and complex pictures
You use the command GOVER to overlay a picture over an existing one drawn with GDISP or GPLOT.
However, the subsequent pictures are treated as independent entities so they
do not take into account the previous picture's layout.
In particular it is advisable to use the display parameter SCREL()
to adjust the size of the overlaid picture to the that of the previous one.
Basic overlay methods
With the display parameters XREL() and/or YREL()
you may place the subsequent pictures relative to the origin of the first one.
Because the overall plotting area size is determined by the first picture
you should plot the rightmost uppermost figure first. Example:
GDISP / XREL(1.0)
GOVER / XREL(0.0)
You may also use the display parameters XRSIZE() and/or YRSIZE()
to allocate a plotting area with a size relative to the first picture's axes lengths:
GDISP / XRSIZE(2.0)
GOVER / XREL(1.0)
You may also produce insets:
GOVER / XREL(0.25) YREL(0.25) SCREL(0.125)
produces a small picture of 1/8 the size of the big one,
located at an offset of 1/4 of the big picture's axes.
Fixed scale overlays
By default each dataset is plotted with its own scale,
Often this causes overlays with different axes.
To improve on this you may specify (once per session)
one of the following
GMODE / FIXEDOVERLAY
GMODE / FOVL
In this case the scale of the preceeding
is kept for all following
To return to the startup default use one of the following
GMODE / NOFIXEDOVERLAY
GMODE / NOFOVL
Suppressing unwanted descriptions
With the display parameters NOXNUM, NOYNUM and NOCOMMENT
you can suppress unwanted axis descriptions:
GDISP / YREL(1.0) NOXNUM
GOVER / YREL(0.0) NOCOMMENT XNUM
Sometimes axis tic numbers from different partial graphs overlap.
You can suppress this by choosing slightly different display limits
which have no visible effect but affect the tic numbering:
GDISP / XREL(1.0) NOSP XMIN(0) XMAX(100)
GOVER / XREL(0.0) NOSP XMIN(0) XMAX(99.9) SCREL(1)
GDISP / XREL(1.0) NOSP XMIN(0.01) XMAX(100)
GOVER / XREL(0.0) NOSP XMIN(0) XMAX(100) SCREL(1)
will plot data from 0 to 100 but avoids the overlap of the 0 and 100 tic numbers.
Complex pictures with EXEC
Very complex pictures which require many commands are best built by
grouping together the gd commands in a script file which can be
executed with the EXEC command. This is also
useful as a documentation how a particular figure was built.