[Plplot-devel] Custom axis labeling update

[Hezekiah M. C. <hez...@us...>]

This is a follow-up to the discussion of custom labeling from this thread:

http://sourceforge.net/mailarchive/forum.php?thread_name=1240743487.4557.51.camel%40sony-sjs&forum_name=plplot-devel

As a brief overview, Steve Schwartz asked about the possibility of
changing the format, layout and position of the plot axis multipliers
- the x10^n labels which may appear for axes with large values.
During the following email thread, I proposed a possible work-around
of allowing custom labeling functions in PLplot and volunteered to put
something together.

The attached patch implements a new function, some related constants
and settings which allow a user to provide custom x, y and z axis
labeling.  The changes made by the patch are:

1. A new option "o" can be added to any x, y or z option string for
plbox or plbox3
2. A new function plslabelfunc has been added to the public API to
allow a user to set a custom labeling function.  The function receives
the axis being labeled and the floating point value where the label
will be placed, along with several other pieces of information, and
can return a custom string with the appropriate label text.
3. New constants PL_X_AXIS, PL_Y_AXIS and PL_Z_AXIS are #define-d in
plplot.h (values 1, 2 and 3 respectively) to more easily identify axes
in a custom labeling function.
4. New options 70, 71, 72 and 73 are added to the last argument of
plenv to support custom axis labeling.
5. The C version of example 19 is updated to show an example of using
(2) and (3), with the first two plot pages now including longitude and
latitude labels in the form of "60 W" and "30 N" respectively.

The first page of the updated example 19 output is attached to this email.

I would like to ask for comments on the patch before I commit it, as
it touches several core PLplot areas.  It should not, as far as I have
been able to test, affect any existing plotting code.  If no custom
labels are requested or defined then the current, default PLplot
labeling behavior is used.

If there are no major objections, I will update the PLplot
documentation and commit the changes.  I can propagate the API and
example changes to the OCaml bindings as well.

Hez

-- 
Hezekiah M. Carty
Graduate Research Assistant
University of Maryland
Department of Atmospheric and Oceanic Science