[GRASS-user] GRASS and layers

[Harri Kiiskinen]

Hello all,

I've always thought that the GRASS vector layer concept is somehow
misleading, while coming from an AutoCAD background by myself. There,
the layers were an integral part of the drawing process, and you could
not do anything without them. In GRASS I learned to think the different
vector maps as layers which can be placed on top of each other and made
to behave in a layer-like way. The GRASS layers I always saw as what the
documentation says, more like different links to background databases. A
recent discussion on this list seemed to have the same message, and some
even considered removing the layers altogether, or at least renaming
them.
	So, you can all imagine my surprise when during the last few days I
have found out, that the GRASS layers  a r e  layers in the sense I had
known, after all. First, when setting up MapServer to show some maps I
had imported from dxf files via v.in.dxf, i noticed, that the layers  c
a n  and  d o  have names: v.in.dxf imported the layer names from the
dxf file, and to access the data via OGR, I  h a d  to use those names;
a layer number would not get any data if a layer name was present. The
names could be found in
$GISDBASE/$LOCATION/$MAPSET/vector/$VECTORNAME/dbln.
	Today, I imported some more complex data from dxf files, again with
v.in.dxf, and suprise, it all went into different layers again! And as I
can select only one layer to display with d.vect layer=, and define
specific colors and everything for it, it appears, that the GRASS layers
are really layers in the AutoCAD sense, too.
	In fact, they are actually better. They provide the database links,
too*, so all the objects can be linked to extensive background data, and
selected on this basis, too. And v.digit provides one interface to
setting and changing these links. What a pity there is no way to edit
only specified layers, in here.

So now, I have two requests: 1. stop downplaying the GRASS layers; they
are at least as nice as AutoCAD layers; 2. Don't you DARE to remove this
wonderful functionality.

As for the further development, it would be nice to have some kind of
access to the layer names. In the long run, of course, it would be nice
to be able to use the layer names everywhere you currently use the layer
numbers, but that probably is non-trivial to achieve. Also, a way to
find out about the existing layers would be nice. Now the only way to
find out what the layers in a vector are is either to look in the above
mentioned file or run v.db.connect -p. For example, v.info would be a
logical choice for this kind of addition.

* So do the newer versions of AutoCAD, but they are a pain to set up, at
least with PostgreSQL...

All praise to GRASS developers,

Harri K.

-- 
Harri Kiiskinen <harri.kiiskinen at utu.fi>