[GRASS-user] Merging stream segments based on order

[Ken Mankoff]

Please disregard last message. The 'merge' tool example uses 'cat', but realized I can select on any table column, and the tool takes care of the multiple unconnected (different) streams/basins.

v.edit map=streams tool=merge where="hack == 1"
v.edit map=streams tool=merge where="hack == 2"
v.edit map=streams tool=merge where="hack == 3"

and then calculate sinuosity with

v.to.db map=streams option=sinuous columns=sinuosity

Seems to work.

Thank you,

  -k.

On 2024-01-02 at 13:53 -07, Ken Mankoff <mankoff at gmail.com> wrote...
> Hi GRASS list,
>
> I'd like to calculate stream sinuosity. I currently do this with:
>
> v.to.db map=streams option=sinuous columns=sinuosity
>
> But the 'streams' vector there is generated from
>
> r.stream.order stream_rast=streams direction=fdir elevation=head
> accumulation=acc stream_vect=streams hack=hack shreve=shreve --o
>
> And is made up of many segments. I'm therefore calculating sinuosity
> of each segment. I believe this underestimates sinuosity. For example,
> a stream can have many short straight lines (sinuosity 1), each
> connected at an angle (sinuosity >1). But the reported sinuosity is
> only 1 for each of the straight segments.
>
> I'd like to merge all connected lines with say, hack order 1, and then
> calculate sinuosity for one much longer segment. The stream vector has
> many basins, so there are many hack=1 segments. The associated table
> has 40k rows. If I limit to where hack==1, there are 6k rows. hack==2
> has 12k rows.
>
> Can anyone suggest how I merge? Looping over basin seems inefficient.
> I see v.edit has a 'merge' tool, but it isn't clear to me how to find
> the cats I want to merge? For each segment I have:
>
> cat|stream|next_stream|prev_str01|prev_str02|prev_str03|prev_str04|strahler|horton|shreve|hack|topo_dim|scheidegger|drwal_old|length|stright|sinosoid|cum_length|flow_accum|out_dist|source_elev|outlet_elev|elev_drop|out_drop|gradient|start_x|start_y|stop_x|stop_y|sinuosity|n_up
>
> I could add two new new columns that are the out_x,out_y of the
> terminal outlet (direction = -1 from r.watershed), build a uniq ID
> from that pair, set that to the category of all of the segments, and
> then merge using that?
>
> Thanks for any suggestions,
>
>   -k.