= Distance source =
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{{{
alter table ccm21.riversegments add column distance_source numeric;
}}}

The distance source is calculated by the following request :
The distance sea corresponds to the distance of the downstream node of each riversegment
The distance source for a riversegments A is the maximum of the distance + length of the upstream riversegment
Note the upstream catchment function does not return the catchment upstream... so we have to use the upstream_segment function
[[Image(source:data/Docs/trac/upstream_segments_and_catchment.jpg,300)]] 

In the ccm we find the cum_length which is the cumulated length of upstream riversegments but not the distance to the farthest source
{{{
select round(max(cum_len_sea+shape_leng) -(select cum_len_sea from ccm21.riversegments where gid =234706)) 
as dist_source from ccm21.riversegments where gid in (select ccm21.upstream_segments(234706));
}}}