downstream trace

[smnorris]

A function returning downstream stream network features would be useful. Particularly as aggregated/simplified features as MVT for a web map query.

Even more fun would be to add the Peace/Mackenzie, Columbia, etc centrelines to the db, making the downstream trace more comprehensive. This would be very simple for major systems. For smaller streams and streams that meander in and out of the province it may require more effort than it is worth.

[smnorris]

#145

[smnorris]

Function added: 6171e3e

Todo:

• wrap in MVT (or test direct performance with pgts)
• add downstream USA blue lines

[smnorris]

Consider adding a boolean parameter that flags whether or not to return side channels.
For fish migration, desired behaviour would generally be the shortest/primary route to the ocean, not all the adjacent/alternative paths?
https://features.hillcrestgeo.ca/fwa_test/functions/postgisftw.fwa_downstreamtrace/items.html?start_blue_line_key=356364114&start_measure=138150

Note that filtering out side channels from the result won't quite work - function needs to support side channel origins that are connected to destination. This might require a recursive query?

[smnorris]

Supporting origins on side channels with a recursive query that processes the geom endpoints is probably fine - only a very small number of features will be used. But just using pg_routing seems like an easier solution, and that would support general upstream/downstream shortest path routing as well.