[GRASS5] Re: [GRASSLIST:3976] Re: intersect sites with polygons?

[Christoph Simon]

On Tue, 2 Jul 2002 11:31:46 +0100
Glynn Clements <glynn.clements at virgin.net> wrote:

> 
> Radim Blazek wrote:
> 
> > As this is one of MANY spatial analysis, it should go to
> > v.mapcalc (already started)
> 
> I've just had a look at that; it doesn't seem to provide much of a
> basis for an actual tool along the lines of r.mapcalc.
> 
> The first thing to decide is the structure of the processing pipeline. 
> E.g. for r.mapcalc, the expression is evaluated for each row of the
> result. An N-parameter function takes N buffers as input, one row of
> each input raster, and stores the resulting output row in the output
> buffer.
> 
> What would the processing model be for v.mapcalc? What would the
> "values" be? Complete vector maps?

Vector maps are intrinsically more complex than raster maps. The
latter has just a point and a value, while the former has a set of
several possible types of objects, each with many possible
properties. The current design of v.mapcalc is essentially the same as
having a set of grass modules and using shell scripts, but implemented
in a program which knows of numbers, maps, points and point lists, and
an anonymous catch-all type `any'. There will be a minimal set of
builtin functions, but most will be dynamically loaded functions. This
way v.mapcalc doesn't need to define what can't be defined: any
attempt to deal with all possible combinations will yield an
explosion.

I still need to code a few things to make visible the complete idea,
when I plan to publish what I've done.

-- 
Christoph Simon
ciccio at kiosknet.com.br
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