On 03/10/08 19:03, Ryan R. Rosario wrote:
[...]
Sorry for the vagueness, but I am thoroughly confused on what goes on with
these attribute tables at times.
See my response below: the lines in connected_lines to not contain ids
and so you cannot connect them to any database table.
I guess, you are trying to apply solution 2b proposed in [1] ? But you
are also trying to get the attributes of the incidents points linked to
the projected points.
As you can read in that mail: "(you might have to use v.db.addtable on
that to create a table first, can't remember)". As I mention below, you
have to do that since v.distance does not create a table.
So, here are the steps I propose (untested):
1) v.distance [...] output=connecting_lines
2) v.db.addtable [...] columns="cat int, inc_cat int"
3) v.distance from=connecting_lines to=incidents upload=cat
column=inc_cat dmax=0 (I suppose that the connecting lines touch the
incident points. If they don't you might have to slightly increase dist)
4) db.copy from="incidents table" to="projected_incidents" (optional,
you can also link directly to the incidents table)
4) v.db.connect -o connecting_lines key=inc_cat [...]
Moritz
[1] http://lists.osgeo.org/pipermail/grass-user/2008-October/046905.html
Moritz Lennert-2 wrote:
On 03/10/08 08:57, Ryan R. Rosario wrote:
I have vector maps called "incidents" (points) and "roads" (lines). For
some
reason, I am getting nothing as output in the final attribute table;
First of all: could you state clearly and precisely what you want to do ?
that
is, the attribute table is not being updated at all. I am sure I am
making
some silly mistake.
[...]
What could I be doing wrong?
This:
> v.distance from=incidents to=roads output=connecting_lines upload=cat
> column=nearest
> #I copied table "incidents" to "connecting_lines" and called it
> "connecting_lines". I used the option
> #key=nearest.
(Second: please be more explicit in the description of your actions. In
this case, for example, please tell us which command you used. I assume
v.db.connect...)
The output map of the v.distance command contains only lines for
visualisation which do not even contain a category value allowing to
identify each line. You cannot, therefore, link the map to a table.
Well, you can, but no records in the table will correspond to a line as
the latter do not have a ids.
Debatedly, v.distance could be enhanced to include some information in
an attribute table accompanying the map, such as from_cat and to_cat,
but someone would have to implement that.
Moritz
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