Strategies for on-the-fly graph generation

Version 2.42 May2013

On-the-fly graph generation is useful for dynamic content web sites and automatic report generation. Ploticus is suitable for these situations since it is a non-interactive command line tool with a relatively small code size.

Prefabs may be used, or your plots can be script-based. With scripts, variables are often passed in via the command line. It is also possible to have your program build a ploticus script on the fly.

There are several strategies for producing on-the-fly web graphs:

Option 1: direct CGI mode

To invoke ploticus in direct cgi mode, you specify a URL that invokes ploticus with the desired parameters, right within an <img> tag,

Option 2: using quisp_pl

A new package called quisp_pl generates web pages dynamically (similarly to php or asp), and ploticus scripts or prefab invocations can be embedded within your code to create dynamic graphs. Download the quisp_pl package and try it. One nice thing you can do with this is create CGI form along with the graph, so users can control various graph parameters... here's a live demo example of this.

Option 3: via perl or python interface

Perl and python interfaces to libploticus have been contributed and are available under "Accessories" on the download page.

Option 4: some other CGI interface to the libploticus API

The libploticus API is freely available; developers can write their own interface to it and invoke as a CGI.

Option 5: invoking pl via the shell

The performance penalty for going this route may not be as much as you'd expect. Generally the procedure is:

    1. generate a unique temp file name for the output
    2. invoke pl via the shell, using the temp file as the output file (-o)
    3. display the temp file using an <img> tag
    4. remove the temp file or set up an automatic process to do so. For example, on unix systems you can place the following command into a crontab and run it every night to automatically remove files that are over one day old:
    /usr/bin/find tmpdir ! -type d -mtime +1 -exec rm -f {} \\;

Option 6: using ploticus CGI via ASP/VBS

This is discussed here: ploticus newsgroup message# 1358

Troubleshooting tips

Here are some troubleshooting tips for running in a webserver-invoked environment:
    Be sure your pl command is executable by world

    You generally can't see anything written to stderr on your web browser, so there could be error messages that you're not seeing.

    Verify that pl is in fact being executed or not. web server environments typically have a very limited command path. Try specifying the full path name of your pl executable. Try it with these arguments:
        pl -diagfile /tmp/myerrs1 -errfile /tmp/myerrs2
    and see what appears in those /tmp files ... if those files aren't created pl is probably not being executed at all. If they are try adding the -debug arg and your args, then check the /tmp files again.

    Determine the directory where your command is being executed. Try making php exec the command pwd ... you may need to give full pathname for your data file, etc.

    Some web server environments may have restrictions on locations where files are allowed to be written. pl needs to write to /tmp and needs to write to create the result png or gif image

    Some web server environments might have restrictions on locations where files can be read from.

    In order to use prefabs, the PLOTICUS_PREFABS environment variable must be available in the runtime environment. PLOTICUS_PREFABS=the directory where prefab scripts reside

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