[GRASS-user] Assign attributes of start and enpoints to connecting lines

[Hanlie Pretorius]

Hi Micha,

Thanks for the reply.

I tried your method using the GUI, and it seems one cannot have a
from_type of 'line', only of 'point' or 'centroid'.

I tried:
v.distance from=c83a_rivers_5km to=c83a_rivers_5km_junctions
from_type=centroid to_type=point upload=to_attr column=Jname
to_column=end_node

And got:
ERROR: Column <Jname> not found in table <c83a_rivers_5km>

Jname is a column in the junctions layer.

If I change the last two options around (obviously wrong):
v.distance from=c83a_rivers_5km to=c83a_rivers_5km_junctions
from_type=centroid to_type=point upload=to_attr column=end_node
to_column=Jname

I don't get an error but no updates either.


I've found another (proprietary) program that can do this, but I was
curious to see if it's possible in GRASS.

Regards
Hanlie




2010/12/9, Micha Silver <micha at arava.co.il>:
> On 09/12/2010 16:38, Hanlie Pretorius wrote:
>> Hi,
>>
>> I'm working in GRASS 6.4.0 on Windows XP.
>>
>> I'm creating a hydrological model and am using GIS to prepare the data.
>>
>> I've split my river layer into about 100 segments and I've digitised
>> the start and end point of each river segment on a points layer.
>>
>> For the points layer, I calculate a 'name' from a prefix and a sequental
>> number.
>>
>> What I would like to do, is to assign for each river segment the name
>> of the start node and the name of the end node to the attribute table
>> of the river segment layer.
>>
>> Can anyone give me pointers on how to do this?
> I think that v.distance can do this. begin by adding two
> attrib columns to your river layer, one for the start node
> label, and one for the end node label. Then run v.distance
> twice to get the labels from the 'name' column from each of
> the node layers. Finally concatenate the two labels together.
> So...
> # Add columns
> v.db.addcol rivers col="start_node varchar(8), end_node
> varchar(8), label varchar(16)"
> # Use whatever size strings you need
> v.distance from=rivers to=end_nodes from_type=line
> to_type=point upload=to_attrib column=name to_col=end_node
> # and again for the start_nodes
> #Now merge the columns
> echo "UPDATE rivers SET label=(start_node + end_node)" |
> db.execute
> # I'm not sure the above '+' will work on all database
> connections. With dbf probably not...
>
>> Thanks
>> Hanlie
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>
>
> --
> Micha Silver
> http://www.surfaces.co.il/
> Arava Development Co.  +972-52-3665918
>
>