Re: [Nlisp-developer] on `save-plot' name and save-plot feature

[Leigh S. <le...@le...>]

Thanks Mirko for your feedback on save-plot. While the default format  
is postscript, the :format keyword parameter to SAVE-PLOT allows  
specifying any of the formats that gnuplot supports.

> We should have a routine to save all the plot data (and hopefully  
> formatting parameters) into a file that can be read at a later date  
> and used to restore a plot.  I would find such a feature  
> tremendously useful.  Especially if the data in the restored plot  
> can be read into a lisp session.

I tend to feel that there are already routines in nlisp-io for saving  
the data that is used to form the plot, .SAVE allows writing the data  
out in a number of binary and text formats. There is a long standing  
plan to implement saving to HDF5 format which can also benefit  
plotting. I find writing a postscript file which is then converted to  
PDF (or using aquaterm to directly write PDFs) in effect achieves that  
plot archiving for my purposes. This could be achieved for those  
platforms that don't do PDF plotting natively by SAVE-PLOT checking if  
the :format parameter is "PDF", and if so, running a ps2pdf converter.

Likewise, if the :format parameter was "archive", this would just  
cause SAVE-PLOT to call .SAVE to write the data to some files. These  
could be read back again with the standard file I/O routines (.LOAD).   
I personally don't favour that approach since the idea of plot  
functions archiving data mixes the two behaviours and I think this  
will just complicate the code. To me, what we need is to slightly  
extend .SAVE to also handle lists of NARRAYs:

(plot (list n-data1 n-data2) (list x-axes1 x-axes2))
(save-plot :format postscript)

can be:

(.save (list (list n-data1 n-data2) (list x-axes1 x-axes2))  
file :format :binary)
then
(apply #'plot (.load file))

> I am not sure how to implement that.  As a start, each window should  
> have an associated variable (object) that stores the names of the  
> data files used by gnuplot, and the list of plot commands.  Upon a  
> (save-plot file-name) the files should be zipped into an archive and  
> an additional file with plot commands stored in it as well.

The problem I see is how to ensure the gnuplot commands that generate  
the plot are archived properly such that they can recreate the plot  
you want. Most gnuplot commands probably can just be replayed with the  
right data filenames, but it means dealing with directories that will  
change between when the plot is originally drawn and when they are  
replayed.

>
> As for saving plots in other formats, how about using names such as  
> `render' or `export'.  `Dump' which I used is too hackerish.
>
> Maybe there is a better name than save-plot for saving plots.

I'm certainly open to renaming SAVE-PLOT, but in naming it that, the  
semantics were considered as that the plot itself is being saved  
(after it has been displayed). So I don't have a problem with the  
concept of saving the plot data and gnuplot commands, but I think it  
might be quite a bit of work to get it running transparently. I also  
suspect the approach may not scale all that well, recreating small  
plots from the original data is practically the same amount of work as  
redrawing the image, but for large complicated data sets, the plot is  
often downsampling and projecting to 2-D the data to produce the image  
and so will be slower than drawing the PDF whenever the plot is  
redrawn within gnuplot.

Leigh
--
Leigh M. Smith
mailto:le...@le...
http://www.leighsmith.com
skype:aussieleighsmith