[GRASSLIST:1357] Re: Web Mapping

[Markus Neteler]

On Thu, Jan 11, 2001 at 08:08:56AM +0100, 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.
That's unusual. Here it runs fine. I can change the resolution like
this:

#write the D_cell file:
export GRASS_WIDTH=100
export GRASS_HEIGHT=200
d.mon start=CELL
d.vect ndsgrenzen col=red
d.mon stop=CELL

#look at it:
g.region rast=D_cell -p
d.mon x0
d.rast D_cell

#reset region to location coordinates:
g.region -dp

# next try:
export GRASS_WIDTH=400
export GRASS_HEIGHT=400
d.mon start=CELL
d.vect ndsgrenzen col=red
d.mon stop=CELL

#look at it:
g.region rast=D_cell -p
d.mon sel=x0
d.rast D_cell

#reset region to location coordinates:
g.region -dp

Works fine and leads to different resolutions.


> What does happen if 2 processes try to access the ressource 
> D_cell at the same time ?
Mhhh, no idea, sorry.
 
> Do I have to write a scedular to avoid ressource conflicts ?
Maybe yes.
 
> As each process may re- g.region the GRASS-database, do I have 
> to lock this ressource also ?
*Probably* yes as the current settings are used.

Maybe this is a little help,

 Markus Neteler