Hello to all Grass users,
Until now I have been working with commercial software. I have installed
WinGrass and made the Spearfish tutorial. I have noticed that Grass is more
oriented to raster processing. Before going on I need to know whether is
possible:
- To create different kind of vector thematic maps based in nodes, lines,
and polygons.
- To link vector entities with registers in a database (for example: a
polygon representing a parcel with an ID to a register that has data like
the name of the owner).
- To query the database via SQL and see the results graphically in the
monitor (for example: show all the parcels that meet a selection condition).
Thanks in advance for your answers.
Regards,
Roberto.
Disclaimer: I am a user, not a developer or expert.
I have noticed that Grass is more oriented to raster
processing. Before going on I need to know whether is
possible:
- To create different kind of vector thematic maps based
in nodes, lines, and polygons.
Yes, you can create thematic maps using d.vect and
d.vect.area. The latter command allows you to specify fill
and line colors for vectors based on their category values.
The legend file lets you specify in some detail how each
category should be displayed.
- To link vector entities with registers in a database
(for example: a polygon representing a parcel with an ID
to a register that has data like the name of the owner).
By juggling the category filenames in dig_cats/ in relation
to the vector geography files in dig/, dig_att/, and
dig_plus/, you can currently achieve this within GRASS that
is, without linking to a database.
There are also a suite of database commands (prefix db.)
that permit you to link to a database and use SQL. I have
not been able to make these commands work BECAUSE I do not
have working ODBC on my linux computer and do not completely
understand the set-up). My understanding is that if ODBC is
working, then these commands work. (This responds to your
inquiry below, too.)
- To query the database via SQL and see the results
graphically in the monitor (for example: show all the
parcels that meet a selection condition).
Finally, my understanding is that GRASS 5.1 (or the
production version thereof) will have much more by way of
vector and database communication built-in.
BTW, would it be possible for someone to explain to new
users, what will be available in 5.1?
Best,
Michael
On Wednesday 27 November 2002 07:51 pm, Michael Ash wrote:
BTW, would it be possible for someone to explain to new
users, what will be available in 5.1?
Nobody knows what WILL be available, but I can tell you what already IS
available:
- link features in one vector to more tables (e.g. lakes and fields sharing
boundaries but with different table structure)
- 3D vectors (you can already query heights of TIN by d.what.vect)
- read directly shapefiles without conversion
- store geometry in PostGIS/Postgres (multiuser write access)
- some features from db.* and pg.* modules are already integrated to standard
modules (for example d.vect map=road where="type = 2"
v.extract input=road output=road2 where="type = 2")
- more database drivers: ODBC, DBF, Postgres, MySQL
- network analysis: d.path finds shortest path between source and destination
node, costs may be assigned both to nodes and arcs (to arcs different in
both directions)
- spatial index - v.build (v.support) accelerated from hours to seconds
- display 3D areas (like TIN) and lines in nviz:
http://mpa.itc.it/radim/g51/chaloupky1.png
- v.digit with GUI (not yet finished):
http://mpa.itc.it/radim/g51/v.digit3.png
- v.surf.rst can read z values and smoothing parameters from any column
in database table
- export any OGR format for which write access is supported by OGR
(including attributes, if supported by format).
Currently Shapefile, TIGER, MapInfo and GML.
PostGIS and DGN should be soon available
- v.clean (break lines at each intersection, remove duplicates) currently
works better than v.spag
Radim
