[GRASSLIST:4833] Re: transition probability

[Radim Blazek]

You have to join the tables in Postgres.
I hope to add join table to v.overlay later.

Radim

Dylan Beaudette wrote:
> On Saturday 13 November 2004 12:45 am, you wrote:
> 
>>Dylan Beaudette wrote:
>>
>>>If it hasn't, I am wondering if there are a couple of vector commands
>>>that could do the following:
>>>
>>>given an input polygon map of several categories, and a line drawn across
>>>these categories,
>>>
>>>1. sample the polygon boundaries(and their respective category) that the
>>>line intersects
>>>
>>>2. put the above information into a new vector line that contains line
>>>segments that have an attribute that matches the category of the polygon
>>>that they intersected.
>>
>>v.overlay
>>
>>Radim
> 
> 
> Seems that I just figured out the answer to my last question in regards to 
> line vector types. 
> 
> However, I now have another perhaps more complicated problem..
> 
> i have two maps:
> 
> t_1 = line map containing a single line
> 
> fresno_west = ploygon map with many polygons, and mulitple attributes per 
> polygon:
> -------------------------
>  db.describe -c fresno_west
> Column 1: cat
> Column 2: AREA
> Column 3: PERIMETER
> Column 4: CA653_A_
> Column 5: CA653_A_ID
> Column 6: MUSYM
> Column 7: MUKEY
> ...
> ------------------------------
> when i use v.overlay with ainput=t_1 atype=line binput=fresno_west btype=area 
> output=r_1 operator=and ...
> I get a map with the following attribute columns:
> ---------------------------
> db.describe -c r_1
> Column 1: cat
> Column 2: cata
> Column 3: catb
> ---------------------------
> 
> this is almost what i want, as each of the line segments in the resulting map 
> (r_1) is labeled with the category number corresponding to the polygon that 
> it intersected in the catb attribute column:
> (http://basho.dept-lawr.ucdavis.edu/~dylan/temp/tp1.png)...
> 
> this is great, but i need to join the attributes from the original polygon 
> file to the new line file r_1. i imagine that it would be a join on:
> r_1.catb ---> fresno_west.cat
> ...which should then allow corresponding attributes from fresno_west (the 
> polygon layer) to be connected to r_1 (the output from v.overlay)...
> 
> i am able to connect the attribute table from fresno_west to r_1 with the 
> command;
> v.db.connect map=r_1 table=fresno_west key=catb field=2 -o
> 
> ...but this does not produce the results that i am looking for as the 
> fresno_west table does not contain a 'catb' column...
> 
> .... perhaps I am not fully comprehending the GRASS 57 vector attribute 
> system.. any ideas?
> 
> many thanks!
>