[GRASS-dev] Python Scripting

[Michael Barton]

Hi Dan,

This sounds intriguing. What we need to ask is what would this gain us  
and how much work would it take.

Michael

On Jul 17, 2008, at 9:00 AM, <grass-dev-request at lists.osgeo.org> wrote:

> Date: Thu, 17 Jul 2008 11:23:58 -0400
> From: "Dan D'Alimonte" <dan at dalimonte.ca>
> Subject: Re: [GRASS-dev] Python Scripting
> To: grass-dev at lists.osgeo.org
> Message-ID: <487F640E.6030704 at dalimonte.ca>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>
> I'm curious if any though has been given to developing an actual GRASS
> library for Python that goes beyond calling executables with system  
> calls?
>
> I'm thinking about a model that encapsulates the GRASS environment and
> allows for both low-level processing like the C library, and high- 
> level
> use of existing modules like shell scripts.
>
> I'll admit I have not given this a lot of though, but a hypothetical,
> and  quickly thought-out, example could be something like:
>
>
>
> from grass import module, layer, cell, parser
>
> def r_add(inLayers, outLayer):
> 	for outCell in outLayer.cells:
> 		sum = cell(type=outLayer.cellType)
> 		for l in inLayers:
> 			c = l.getCellAtSameLocation(outCell)
> 			if c.value==cell.null:
> 				sum.value = cell.null
> 				break
> 			sum.value += c.value
> 		outCell.value = c.value
> 	outLayer.commit()
> 		
> if __name__ == "__main__":
> 	# Set up module information here
> 	# Set up and run parser
> 	# Open input layers
> 	# Create new layer for output
> 	# call r_add()
> 	# close layers	
>
>
>
> I don't know if this would even be feasible, but I think it would  
> make a
> nice addition to GRASS's Python support. If done right it would even
> allow other python-based GRASS modules to be called-on without  
> having to
> make a system-call (eg. from raster_add import r_add).
>
> As to existing modules, what about a helper function to access then?
>
> module.executeModule( name="r.stats", options={ "input":
> "elevation.dem,slope,aspect", "fs": ",", "output": "elev.csv"},
> flags=["q", "1", "n", "g"] )
>
> It was just a thought, and would require a lot more thought and work  
> to
> design properly. I, frankly, do not have enough understanding of GRASS
> internals to even know where to begin.