[GRASS5] Multiple attribute support in GRASS5.1:someconsiderations(long)

[Roger S. Miller]

Glynn Clements wrote:
 
> I'm not sure that I understand what's being proposed, but some of the
> comments seem to be suggesting storing drawing attributes in the same
> file as the actual vector data (coordinates etc).

Glynn, I don't think that is what was contemplated, but we didn't cover
it in that much detail so I could be wrong.

I think the new vector format will include a database of attributes
intended to be considerably more comprehensive then the current system. 
I asked that the database include drawing attributes for the vector
object.

I envision that this will require at a minimum a set of default
attributes with one set of drawing attributes for each type of vector
object.  The defaults would probably be stored somewhere in "etc" and
would be installation-wide defaults.  A user would be able to customize
those defaults, with the attributes being filed in user space.  One of
those sets of defaults would be used to initialize the attributes for
any drawn vector object.

That level of attribute specification would be very general.  One set of
attributes for all area edges, and so on.  It would require no more
detail than the developers want to build into the vector structure.  If
they find a need for 5 different line types, or 3 different point types
then the general database would include attributes for 5 different line
type and 3 different point types, but no more.

In addition, I would like to see an additional set of attributes that
might be handled in a way similar to 3dviews, or regions.  It would be a
much more detailed set of attributes stored as a table in the database. 
It might specify for instance that a line in category A is pink, 2 mm
wide and solid, while a line in category B is green, 1 mm wide and
dashed.  The database probably should allow specification of attributes
for each drawn object.  The user would build, modify and select the set
of attributes he wants to use, and that same set of attributes would be
available for use in preparing hard-copy product.

The user-level commands necessary to use the detailed attributes don't
currently exist.  In fact, I don't think that GRASS currently has the
capability of drawing with very many different attributes.  All I'm
asking at this time is that the vector database format should be planned
to allow that capability.


Roger Miller