Drawings
ctioga2 has a series of functions to draw elements which are not
data points in themselves, but to help understand and read data.
Basic drawings
Let’s first annotate a gaussian curve with a line and some text:
math /xrange=-3:3 margin 0.03 plot exp(-x**2) l = $(eval 'sqrt(log(2.0))') draw-line -$(l),0.5 $(l),0.5 /line-style Dashes draw-text 0,0.3 'Half height width: $w = \sqrt{\ln 2}$' /text-width=3cm
Note how we used the eval function to
compute the value of the half-height width.
Tangents
ctioga2 features a very simple way to draw tangents on a curve,
using the draw-tangent command:
math /xrange=-3:3 margin 0.03 plot x**2 draw-tangent 0.3 draw-tangent 0.7 /xto 2 /color black draw-tangent 0.1 /yextent 2 /color blue
In the first form, without options, draw-tangent only draws
an arrow head (in real, a marker) along the curve at
the position asked (here, 0.3, which means “at 30 %”). In the second
form, we ask a full line that will extend until x = 2. Of course,
you can use also /xfrom, /yto and so on. In the last form, one
says how long the arrow is in y units. Beware of the sign, though:
in this case, as the slope is negative, asking for a positive
/yextent makes it go backwards.
Images
Starting from ctioga2 version 0.10, it is possible to include JPEG
or PNG images (there are some restrictions on the type of PNG/JPEG
images that can be handled), using the draw-image
command. We’ll use imagemagick’s
rose for the
demonstration:
math /xrange=-3:3 margin 0.03 plot sin(x**2) draw-image rose.jpg -2.5,-0.3 2.5,-0.7 /transparency=0.4 draw-image rose.jpg -2.5,0.9 2.5,0.5 /aspect-ratio=contract
To include a file, just specify the image file, the top-left corner
and the bottom right corners of the image. By default, ctioga2 just
follows your instructions for the corners, which will probably result
in the image’s aspect ratio not being respected. If you care, use
either /aspect-ratio=contract or /aspect-ratio=expand to preserve
the aspect ratio by respectively not exceeding the original rectangle
in the first case and not being smaller than it in the second one.