Using DATAPLOT with the Web

1. Generating Dataplot output for web applications
2. Integration with the NIST/SEMATECH e-Handbook of Statistical Methods
3. Using Dataplot with CGI scripts
4. Robert Lipman's Web Dataplot software
5. Downloading files for using Dataplot with the web

• Dataplot text output
• Dataplot graphics

1. GIF (graphics interchange format)
2. JPEG
3. PNG (Portable Network Graphics)
4. SVG (Scalable Vector Graphics)

Given the available options for incorporating graphics into web pages, Dataplot provides the following options.

1. On Unix, Dataplot can generate PNG and JPEG format graphics directly. The JPEG driver is not available on all Unix implementations. Also, these drivers use an external library (specifically, the GD library), so if your local implementation was built from the source (rather than being a downloaded executable), then check with your local implementor to see if the PNG/JPEG driver is available. We plan to port this driver to the Windows version of Dataplot. More information for the PNG/JPEG driver is available in the online Reference Manual.

2. Dataplot supports a SVG driver on all platforms. More information for the SVG driver is available in the online Reference Manual.

3. Another alternative is to generate a Postscript graph and then use one of the free or commercial image conversion programs to convert the Postscript graphic to GIF or JPEG. One advantage of this approach is that you can utilize the high quality typeset Postscript fonts. The disadvantage is that you have to go through an extra step in order to generate a web compatible format.

1. Use the CAPTURE command to an ASCII file.
2. Within a web page, enclose the output in the CAPTURE file between a <PRE> tag and a </PRE> tag.

CAPTURE HTML <file-name>

Note that an additional feature of the HTML option is that if DEVICE 2 is set to either PNG/JPEG or SVG, the graphics will be incorporated into the web page using the IMG tag.

You can use the WEB command to view the generated HTML output from within the Dataplot session. For example,

SKIP 25
READ RIPKEN.DAT Y X1 X2
ECHO ON
CAPTURE HTML C:\TABLE.HTM
TABULATE MEAN Y X1
CROSS TABULATE MEAN Y X1 X2
END OF CAPTURE
WEB file://C:\TABLE.HTM
      

device 1 x11
.
skip 25
read berger1.dat y x
.
line blank solid
character x blank
echo on
capture html fit.htm
set ipl1na data.png
device 2 gd png
title original data
plot y x
device 2 close
fit y x
set ipl1na pred.png
device 2 gd png
title predicted line
plot y pred vs x
device 2 close
end of capture
.
web file:///home/heckert/dataplot/solaris/fit.htm
      

1. If DEVICE 2 is set to Postscript, Dataplot will automatically invoke Ghostscript to convert the Postscript file to JPEG format. It will also add the appropriate <IMG> tag to the HTML file. This capability is supported under Windows and Unix. Enter HELP CAPTURE for details.

2. The SET POSTSCRIPT CONVERT command can be used to specify one of several devices. When a Postscript device is closed, Ghostscript will automatically be invoked to convert the Postscript output to the specified format.

   PDF (Portable Document Format) is one of the supported devices. For PDF, the CAPTURE HTML will automatically put a link in the HTML page to the PDF file. PDF may be preferable to JPEG if you need to preserve higher image quality.

   Enter HELP POSTSCRIPT CONVERT for details.

3. The SET HTML HEADER FILE and SET HTML FOOTER FILE comamnds can be used to specify files that will be used for the header and footer, respectively, of the generated HTML file. Enter HELP HTML HEADER FILE for details.

• A check is made to see if Dataplot is currently running.
• If a Dataplot session is currently running, the macro is executed in the currently open session. The check for a currently open Dataplot is accomplished by the Tcl/Tk scripts that implement the Dataplot graphical interface.
• If no Dataplot session is currently running, the Dataplot software is invoked and then the macro is executed.
• In either case, the Dataplot session remains remains open (unless the macro explicitly closes Dataplot).

This approach makes it possible to execute macros successively. This is quite useful in the context of the Handbook case studies. That is, the user can step through the case study in small, easily understood steps.

• Dataplot and the web page are in separate windows. This can be an advantage if you want the user to be able to view explanatory text while also viewing the Dataplot output.
• You can implement fairly involved macros in small, manageable steps.
• If the Dataplot session is left open, the user can execute Dataplot commands independently of the web page.
• Dataplot is run on the users local platform, not the web server. This can help minimize the load on the server.

The primary disadvantage of this method is that Dataplot needs to be installed on the user's local platform.

• A link to the macro needs to be incorporated in the web page. You can view the HTML source for the Dataplot case studies in the Handbook. For example, check the HTML source for one of the eda examples. The Dataplot macros are contained in files with a ".dp" extension. These macro files are stored with the other HTML files on the server. Any needed data files can be added to the data sets directory where the built-in Dataplot data sets are stored.
• Both the web server and your browser need to be configured to know how to handle a ".dp" file. The link contains instructions for how to do this for the most common browsers and the most common platforms.

In general, this approach is useful for tutorial type web pages. That is, you want to teach your audience how to perform a particular analysis using Dataplot.

CGI scripts are most commonly written in Perl, although they can also be written in C or other scripting or programming languages.

We do not document the details of implementing this since there are many books on writing CGI scripts available. This approach has been used by at least one project at NIST for a production system.

The CGI approach can be used with many different programs. There are no particular issues that you need to be aware of when using Dataplot this way. The fact that you can write command driven macros in ASCII files means that Dataplot is well suited for this approach.

• The software does not need to be installed on the user's local system.

The disadvantage of this method is:

• For a heavily used site, running a number of Dataplot applications simultaneously can put a heavy load on the server.

This approach is useful if you simply want to use Dataplot as a computation engine or to generate a specific type of plot dynamically. In this case, the end user may or may not care whether or not Dataplot was used for the computation.

This is a similar idea to CGI scripts. Basically, you have a web form that accepts certain parameters. Then ASP and VBSCRIPT are used to generate a Dataplot macro on the fly and Dataplot is invoked to run the macro and return the results to a web page.

If you would like more information about this approach, contact Alan Heckert.

One possible application of the web Dataplot software would be as an online "problem solver". That is, if your site has a specific set of problems with a standard solution, you could modify the web Dataplot scripts to create forms and run macros that solve these particular problems.

Note that you will need to modify the source provided to fit your own application. These sources are provided as a basic framework for developing your own web applications using Dataplot, not as ready to use scripts. This source is provided "asis" and we do not offer any additional support for them. If you want to adapt these to your own applications, you should have some basic web development experience (you should not need a lot, but should have a handle on the basic concepts).

1. If you are interested in an approach similar to the NIST/SEMATECH Engineering Statistics Handbook, then you don't really need any additional software other than the user installing Dataplot on their local machine. The discussion above provided links to pages that discuss how to configure your browser on the most popular platforms (other platforms should be similar) and a link to a page that discusses configuring your web server for Dataplot macros.

2. Probably the most common approach will be to write a CGI script. You can download a C program called "step1.c" and the corresponding HTML Form page called "step1.html" that initiates the call. The step1.c program also uses util1.c. These sources were provided by Dale Bentz of the NIST Building and Fire Research Laboratory. They are from a web project that uses Dataplot as an underlying computational engine. In this case, the end users do not know or care that the computations and graphs are being generated by Dataplot.

   You compile "step1.c" and "util1.c" to create an executable called "step1" that is stored in the appropriate "cgi-bin" directory. You will need to make changes to the C code and HTML form to adapt it to your specific application, but these sources provide the basic framework. Note that "step1.c" makes a call to the "convert" program. The convert program is a program that converts Dataplot graphs in Postscript format to "gif" format for web viewing. You will need to replace convert with whatever conversion utility you have available on your site (or have Dataplot generate PNG format graphs directly).

   The C program could also be easily replaced by a Perl script. Although I intend to provide an example of this, I haven't had time to put this together yet.

   NOTE 3/8/2001: I now have a Perl based example available for downloading. This is just a simple example that accepts some data from the user and generates a simple run sequence plot and returns a PNG file to the browser. You will need to modify it for your own applications, but it shows the basic steps involved. Dataplot has added support for PNG and JPEG graphics. This is based on the GD library of Mark Bouttel (this is the library used by Perl and numerous other software programs for PNG/JPEG graphics). I will be updating the Unix executables on the ftp site the week of March 13, 2001. Support for PNG and GIF on the PC executables will be added in a few weeks (hopefully). For Dataplot executables that do not support the PNG or JPEG graphics, you will need to add an extra step to convert Dataplot Postscript output to either GIF, JPEG, or PNG. The example includes a HTML form page, a Perl script to parse the form arguments, run Dataplot, and return a PNG format graph, and the sample Dataplot macro.

3. Bob Lipman's web dataplot code requires the following:
   • You need Tcl/Tk and Expect (these are typically already downloaded and installed if you are running the GUI version of Dataplot).

   • In addition, it requires the Tcl/CGI library from Don Libes (the author of Expect).

   • A tar file of cgi scripts is available. This file should be untarred in your "cgi-bin" directory. The main script is "wdpi.cgi". The file "wdp.cgi" is the HTML file that initiates "wdpi.cgi". This can be installed as part of your web pages.

   This approach provides a bit slicker approach than the C program or Perl script provided above. The downside is that it requires more web knowledge and additional software installation. I would generally recommend starting with the C program (or Perl script). Then if you desire a more sophisticated approach you can try the web dataplot scripts.

Date created: 6/5/2001
Last updated: 9/10/2002
Please email comments on this WWW page to sedwww@cam.nist.gov.