[GRASS-user] Unique IDs for network segments

Johannes Radinger johannesradinger at gmail.com
Fri Dec 4 04:52:42 PST 2015


Moritz,
thank you! Your proposed approach solved my problem!


On Thu, Dec 3, 2015 at 3:04 PM, Moritz Lennert <mlennert at club.worldonline.be
> wrote:

> On 03/12/15 14:19, Johannes Radinger wrote:
>
>> Hi Moritz,
>>
>> The two-step v.category approach (del + add) and an additional v.to.db()
>>   was the
>> right way. Now I have the problem that there are 3 categories reported for
>> one single line that got split into to (1 old cat + 2 new cats). The old
>> category is still
>> associated with attributes but the two new rows are empty. How can
>> I get an attribute table that contains only rows for the new cats with
>> the attribute information
>> of the old category?
>>
>> [...]
>
>> # Remove existing cats
>> v.category --overwrite input=test_net type=line cat=-1
>> output=test_net_nocat option=del
>>
> [...]
>
>> # Add new cats
>> v.category --overwrite input=test_net_nocat type=line
>> output=test_net_newcat option=add
>> v.to.db map=test_net_newcat type=line option=cat columns=cat
>> #############
>>
>
> Instead of removing the existing cats, add new cats in a new layer and
> transfer the info into that layer's attribute table:
>
>
> v.category --overwrite input=test_net type=line output=test_net_newcat
> option=add layer=3
> v.db.addtable test_new_newcat layer=3
> v.db.addcolumn test_net_newcat lay=3 col="col1 int, old_cat int"
> v.to.db test_net_newcat layer=3 op=query col=col1 query_layer=1
> query_colum=col1
> v.to.db test_net_newcat layer=3 op=query col=old_cat query_layer=1
> query_colum=cat
>
> Just make sure to set arc_layer=3 in the network analysis modules.
>
> If you really want to have arcs in layer 1, you can use v.category
> op=transfer, but you will also have to change table connections of the
> layers with v.db.connect.
>
> Moritz
>
>
>
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