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

GRASS GRASS user
1

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?

Thanks
Hanlie

2

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
_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

This mail was received via Mail-SeCure System.

--
Micha Silver
http://www.surfaces.co.il/
Arava Development Co. +972-52-3665918

3

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@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
_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

This mail was received via Mail-SeCure System.

--
Micha Silver
http://www.surfaces.co.il/
Arava Development Co. +972-52-3665918

4

On 12/10/2010 08:19 AM, Hanlie Pretorius wrote:

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'.
   

Yes, you're right. Sorry for misleading you. The 'from' map can be only points, so this won't help to get the node labels into the rivers table.