On 11/10/11 10:26, Sebastian Schubert wrote:
On Tuesday 11 October 2011 01:17:15 Richard Chirgwin wrote:
On 11/10/11 4:02 PM, [email protected] wrote:
Hi,
using 6.4.1, I imported a vector shape file which includes a
tables. This table got a "cat" column by grass (which I don't
need, I think) and already has a "key" column. In addition, I have
got another table which also has a "key" column. Using both "key"
columns, I want to combine both tables. How can I do that? I was
able connect, as a second layer, the additional table to the
vector data using the "key" column but then as far as I can see it
is not really connected to the first table.
I guess this is a standard procedure but I was not able to find the
solution.
Thanks
Sebastian
Sebastian -
I think you're asking to connect two tables to the same map?
Yes, I think so.
The two tables need to refer to the same features, and you use
v.db.connect
Note that you can specify a different name for the key column using
the key= parameter.
I think, this is what I tried. Here is what I did:
I imported the map baubloecke.shp. It already includes data (which is
then called table "baubloecke":
GRASS 6.4.1 (Soldner):~> v.db.connect -p baubloecke
Vector map<baubloecke@Berlin> is connected by:
layer<1> table<baubloecke> in database
</home/schubert/grassdata/Soldner/Berlin/dbf/> through driver<dbf> with
key<cat>
Ok, it is connected with key "cat" which has been introduced by grass, I
think. The table "baubloecke" includes the column I want, as well as the
table "bbdb":
GRASS 6.4.1 (Soldner):~> db.columns baubloecke
cat
ELEMNAME
KLASSENNAM
SCHLUESSEL
GRASS 6.4.1 (Soldner):~> db.columns bbdb
SCHLUESSEL
BLOCKART
FLALLE
NUTZ
FISNUTZUNG
TYP
TYPKLAR
VG
STSTRTYP
STSTRNAME
I connected bbdb to the map:
GRASS 6.4.1 (Soldner):~> v.db.connect -o map=baubloecke table=bbdb
key=SCHLUESSEL layer=2
The table<bbdb> is now part of vector map<baubloecke> and may be
deleted
or overwritten by GRASS modules
Select privileges were granted on the table
GRASS 6.4.1 (Soldner):~> v.db.connect -p baubloecke
Vector map<baubloecke@Berlin> is connected by:
layer<1> table<baubloecke> in database
</home/schubert/grassdata/Soldner/Berlin/dbf/> through driver<dbf> with
key<cat>
layer<2> table<bbdb> in database
</home/schubert/grassdata/Soldner/Berlin/dbf/> through driver<dbf> with
key<SCHLUESSEL>
I tried to verify the connection using the wxpython gui. I opened the
map there (tried both layer 1 and 2). Using the "Query raster/vector
map(s)" tool, I was able to only get information from the layer 1 or the
original table when clicking on a polygon.
Ok, maybe table 1 has to be connected also via the key "SCHLUESSEL" so I
tried:
GRASS 6.4.1 (Soldner):~> v.db.connect -o map=baubloecke
table=baubloecke key=SCHLUESSEL layer=1
ERROR: Data type of key column must be integer
GRASS 6.4.1 (Soldner):~> v.db.connect -o map=baubloecke
table=baubloecke key=3 layer=1
ERROR: Missing column<3> in table<baubloecke>
I do not understand this... Apparently, grass does not accept the key
SCHLUESSEL so I tried the number of the column (?) 3. No success,
either.
You are mixing up two different things here:
1) A vector map in GRASS can be (but does not have to be) connceted to
an attribute table. Any object in the vector map can have a category
value (sort of an identification number). If the map is connected to a
table, this table has to contain a column which contains these category
values. By default, this column is called 'cat' (but you can give it any
arbitrary name). The information about which table a map is connected to
and which column in this table contains the relevant category values is
managed with v.db.connect.
2) You can connect a map to different tables by using layers, but this
is not what is needed here and is quite complex to grasp, so I'll leave
it out here.
3) What you are trying to do is not to connect the map to your second
table (bbdb), but rather to link the table bbdb to the table baubloecke.
In GRASS, the classical way to do this is to a) import bbdb into the
database (which you seem to have done, but we have no info on how) using
db.in.ogr and b) join the two tables using v.db.join. However, this last
command does not suppport the dbf backend for attribute table handling.
You, therefore, have to use another backend, such as the SQLite backend
(see more info here:
http://grass.osgeo.org/grass64/manuals/html64_user/databaseintro.html).
So, in summary, no need to use v.db.connect, but rather, use the SQLite
backend and use db.in.ogr and v.db.join.
Moritz
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