[GRASSLIST:1356] Re: Web Mapping

[Andreas Lange]

Hi Michael,

m.malicky at landesmuseum-linz.ac.at wrote:
> 
> Hi!
> 
> Currently I am developing a web mapping tool for GRASS mainly
> with PHP for our biodiversity Database.
> As I am using the CELL driver for generating pictures I have the
> following questions:
> 
> How can I reset the CELL driver ? - changing the vars
> GRASS_WIDTH and GRASS_HEIGHT to another value after using
> the driver gives me error messages.
You have to stop and restart the CELL driver (d.mon stop=CELL; export
GRASS_WIDTH=300; d.mon start=CELL). This will need some time as the
memory is allocated every time.

> What does happen if 2 processes try to access the ressource
> D_cell at the same time ?
That should never be done. Even if it does not crash it will not produce
anything reasonable. 
One setup would be to use a temporary mapset within the current location
for each process to avoid this. Or the CELL code could be modified to
use a name from an exported variable (see HTMLMAP code how this can be
done). 

> Do I have to write a scedular to avoid ressource conflicts ?
??

> As each process may re- g.region the GRASS-database, do I have
> to lock this ressource also ?
GRASS IMHO does not support multiple useres (processes) in the same
location and mapset at a time. This setup will not work. Why not
creating a temporary mapset for each process? This would require
cleaning up after the task is done, but otherwise avoid the
locking/resource problems you mentioned. 

And not to forget: last time i examined the CELL driver in
GRASS5.0beta10 it was broken somehow. Had no time to find the problem. 

Do you know the mapping tool from Frederico Ponchio:
www.ambientepi.arti.beniculturali.it:2020/demo/index.html ?
Perhaps you can use this or get some ideas about web-mapping with GRASS
from there. 


cu,

Andreas

-- 
Andreas Lange, 65187 Wiesbaden, Germany, Tel. +49 611 807850
Andreas.Lange at Rhein-Main.de - A.C.Lange at GMX.net