[GRASSLIST:7750] Re: for grass6: Are there basic data docs? (atts, cats, etc. question)

[Markus Neteler]

Hi Bart,

I am currently working on improvements in the GRASS 6
Programmer's Manual. I think that you indications below
must be addressed.

I would need a person to review a bit the updated manuals,
are you interested/willing to have a look?

Regards

 Markus

On Thu, Jun 30, 2005 at 02:20:43PM -0300, Bart wrote:
> Hi again.
> 
> I'm sorry to be a bother, but I'm confused. 
> 
> I haven't started doing anything complex yet,
> but want to know GRASS 6's data setup, because
> I've been reading documentation and tutorials,
> which have mostly succeeded in confusing me,
> or not being very clear on what version they do or
> do not apply to.
> 
> I'm mostly interested in what exactly can be done
> with categories and attributes, and even the exact
> distinction between and definition of those two.
> 
> 
> Am I right in thinking that each vecture feature
> inside a vectormap has zero, one or more
> layer,category tuples?
> 
> Also, that you can (not must) create attribute
> tables which are referenced by the layer, and
> rows which are essentially referenced by that
> <DEFANGED_layer,category> pair? (the grass 5.1 vector
> architecture nor the 5.7 vector format and api
> doc seems to mention any layer related things)
> 
> Is it purely up to the user to assign meaning, 
> to create, modify and query with only SQL?
> Is that what attributes are, and to what degree
> can GRASS commands actually use these?
> 
> 
> I found a diagram in the grass6 documentation
> called something grass51, and an explanation
> with grass5.7, so am I right in thinking all
> the above (including layers) was introduced and
> hasn't changed much since 5.1? 5.7?
> 
> 
> I'm interested in exporting data with 
> v.out.ascii. I assume the category lines
> are <DEFANGED_layer,cat> pairs. (or are they field,cat?)
> 
> I suppose any attribute exporting actually
> needs human intervention because they
> defined the actual meaning.
> 
> 
> Also, about the features themselves:
> I assume that v.out.ascii outputs
> level 1 data (ie. no islands and partial
> arcs, but separate areas and such)
> 
> 
> Incidentally, how are centroids, once 
> v.out.ascii'd, linked to an area? 
> And are they, as the grass 5.1 vector
> architecture document suggests, the
> only way to assign categories to areas?
> 
> 
> 
> Thanks in advance,
> --Bart Alewijnse

-- 
Markus Neteler     <neteler itc it>       http://mpa.itc.it
ITC-irst -  Centro per la Ricerca Scientifica e Tecnologica
MPBA - Predictive Models for Biol. & Environ. Data Analysis
Via Sommarive, 18        -       38050 Povo (Trento), Italy