[R] Using jpeg() function over cgi

[michael watson (IAH-C)]

Again, thank you one and all for your help!

My web-server is apache, and simply adding the following line to httpd.conf solved my issues:

SetEnv DISPLAY :0.0

:-D

Mick

-----Original Message-----
From: michael watson (IAH-C) 
Sent: 16 June 2003 14:52
To: 'r-help at stat.math.ethz.ch'
Subject: RE: [R] Using jpeg() function over cgi


OK, thanks for all your help :-D
  
Sorry for not observing normal e-mail help list rules - I am running SUSE 8.1 professional.

If someone coule try and explain a little as to why jpeg() can be used when I run the script as the user httpd runs as, and why it can't when it is run from a cgi script by the same user, then I may be able to get a handle on the problem.  

I have tried using bitmap() instead but quite frankly the images produced are just not of the same quality, either using type="jpeg" or type="png256" and messing around with resolution - they just look more grainy and the circles are, well, more square.

So i guess my REAL question is how do i get images on the same quality over cgi if I am not using the jpeg() function?

And in theory it is an R question, as my linux sys/admin doesn't have a clue why we're getting X11 error message over cgi because he hasn't got a clue how the jpeg() R function works.  The documentation states:

"they may not be usable unless the X11 display is available to the owner of the R process"

Well i run httpd as a user called "base" and if i log in to a shell as base, trust me the X11 display IS available then.  Sooooo, if someone could explain WHY jpeg() won't work over cgi, then i can explain to my sys/admin and he can fix it for me.

OR alternatively, if someone can explain to me how to coax bitmap() into producing images of the quality of jpeg()...??

Thanks
Mick

-----Original Message-----
From: Prof Brian Ripley [mailto:ripley at stats.ox.ac.uk]
Sent: 13 June 2003 16:02
To: michael watson (IAH-C)
Cc: 'r-help at stat.math.ethz.ch'
Subject: Re: [R] Using jpeg() function over cgi


Yes, it has been solved and discussed in the R-help archives many times.
The help(jpeg) page is pretty explicit too.  One alternative is bitmap().

To use jpeg() under a Unix-alike you need to set up an X server that your
R process can use.  It's a bit hard to help you do that when you don't
even mention your OS (I am inferring it is a Unix-alike), but you may be
able to solve the permissions problem or you may be able to set by a
server by something like Xvfb.  In any case, it is not an R problem


On Fri, 13 Jun 2003, michael watson (IAH-C) wrote:

> I have seen a few posts to this list regarding problems accessing the
> x11() device over cgi - namely, when trying to create a graphic using

No, not the x11() device, but the jpeg() device.  They are not the same!

> the jpeg() function, everything is fine from the command line but it
> won't work over cgi, producing the error:
> 
> "Unable to open connection to X11 display"
> 
> Has anyone actually solved this particular problem satisfactorily?
> 
> Please reply direct to me as I am not a member of the list (yet!)


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595