[JDEV] Idea: Jabber for instrument control

[mark at mjwilcox.com]

How about as an option for the images to use the new Scalable 
Vector Graphics (SVG) image standard. One of the benefits of 
SVG is that it's an XML based format. 

The Apache group (courtesy of work donated by Sun) has an 
excellent Java API and viewer called Batik (xml.apache.org/batik).  
I've run it on Linux and it works pretty cool (don't know if does 
animations yet).

And I already think Batik has code to transform from SVG to JPEG 
& PNG. Thus you could use Jabber as your transport mechanism 
(and you could just use normal Jabber messages, don't need 
OOB). Then either use an SVG viewer or convert to another format 
for Web display.

There's also a SVG Perl module (sorry don't have URL). 

 Adobe has an SVG viewer for Windows and Mac at 
http://www.adobe.com/svg/viewer/install/beta.htm.

The SVG homepage is at:
http://www.w3.org/Graphics/SVG/

Good luck,

Mark


On 6 Jan 01, at 10:40, A.M. Kuchling wrote:

> I'm wondering about using the Jabber framework for instrument control,
> and would like to get some advice on the design.
> 
> As part of my work, I've been working on a system for controlling a
> microscope over the Internet; see
> <URL:http://www.mems-exchange.org/software/microscope/> for code and
> details.  While the system does work, it's not very reliable for a few
> reasons, one of which is that handling both the hardware and TCP/IP
> connections in one multithreaded process is tricky.  Sometimes the
> hardware hangs for a second or two, or does something unexpected,
> which causes a crash or hang.  I'd like to reuse other software in
> order to avoid having to write and debug a server on my own, and
> Jabber seems like the best candidate.  I'm thinking of the following
> arrangement:
> 
> * Run a Jabber server on the microscope's computer.
> 
> * The process controlling the hardware is also a Jabber client, so it
>   receives commands through the contents of Jabber messages (perhaps
>   using SOAP, perhaps some new DTD I'll invent), performs the command,
>   and returns a message with the new microscope position, settings,
>   etc.
> 
> * Users run client software that also act as Jabber clients, receiving
>   the special messages from the microscope and displaying them
>   appropriately.
> 
> The big question is how to deal with images?  Some microscopes have
> slow digital cameras (3 frames per second, max), but some have
> framegrabbers (30 frames per second).  The jabber:x:oob namespace
> provides a way to send a URL to be retrieved by the client, but this
> seems unappealing; the client has to initiate the retrieval of an
> image, rather than just having it be sent along.  The server would
> also need to be running another server (HTTP, FTP, or something) in
> order to let clients retrieve images, which goes against my goal of
> reducing the complexity of the system.  Images should really be pushed
> at the client, not pulled by it.  
> 
> Images could be base-64 encoded and embedded in Jabber's XML messages,
> at the cost of increasing image size by 33% and requiring more XML
> parsing.  (Or perhaps the image data could be embedded in a CDATA
> section, but character encodings make this seem dodgy.)  Does this
> seem practical?  Can Jabber servers parse only the headers of messages
> in order to route them, or does the whole message have to be parsed?
> Would there be some other way of sending binary files along?
> 
> On a related note, can messages be sent to multiple recipients and
> routed without copying the message more often than is needed?  For
> example, if client A was connected to server 1 and sent a message to
> clients B and C, connected to server 2, are the Jabber servers smart
> enough to send only one copy of the message from server 1 to 2?  And
> can messages be marked as "bulk", so the servers can drop them if
> needed (for example, if a user on a slow connection is using a 30
> frame/sec microscope, there's no point in forcing every frame at them.
> 
> --amk
> 
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> 
> 


Mark Wilcox
mark at mjwilcox.com
Got LDAP?