[postgis-users] Trace network from each source node and check that the trace reaches the sea

[Shaozhong SHI]

In hydrological network, how to trace network from each source node and check whether the trace can reach the sea?

Any examples?

Regards,

David

[Stephen V. Mather]

Hi David,

This is a good example. I have modified this to walk networks before, and it's a minimal and understandable example:

http://blog.cleverelephant.ca/2010/07/network-walking-in-postgis.html

There may be some better ways to do this, as the postgres tooling has changed quite a bit. The use of a function may be precluded by some modern fancy join type. Others can speak better to that than I can these days.

Also, if you don't mind installing one more thing, pgrouting will do network traversal much more efficiently than a WITH RECURSIVE network traversal:

https://pgrouting.org/

Cheers,

Best,

Steve

On 12/30/21 4:13 PM, Shaozhong SHI wrote:

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[Shaozhong SHI]

Hi, Steve,

I had a quick look at it and looks very interesting.

Can one walk ad traverse from source nodes identified in a collection of links and nodes in a river system and check out whether Strahler stream orders are correctly set?

Regards,

David

[Shaozhong SHI]

Hi, Steve,

I cannot see the pictures.

Regards,

David

On Thu, 30 Dec 2021 at 23:36, Stephen V. Mather <s...@clevelandmetroparks.com> wrote:

[Shaozhong SHI]

Hi, Steve,

Your demonstration script does work.

How to deal with the following scenario?

Suppose that we are handling 3D line strings.  We want to trace walking down the network.  If there be any line string not properly formed (namely, it does not present a consistent walking down).

How best put a check so that walking down is stopped?  And, we can report the missed formed line segment?

Regards,

David

On Thu, 30 Dec 2021 at 23:36, Stephen V. Mather <s...@clevelandmetroparks.com> wrote:

[Shaozhong SHI]

Hi, Steve,

The network-walking-in_PostGIS sometimes produces additional straight lines.

Why does that happen?  How to make sure that resultant lines are correct?

Regards,

David

On Thu, 30 Dec 2021 at 23:36, Stephen V. Mather <s...@clevelandmetroparks.com> wrote:

[Shaozhong SHI]

Hi, Stephen,

Can your approach be used for checking continuity for names, while walking along?

Regards,

David

On Thu, 30 Dec 2021 at 23:36, Stephen V. Mather <s...@clevelandmetroparks.com> wrote:

[Shaozhong SHI]

A strange thing is that this recursive query got stopped by the following error.

ERROR:  invalid memory alloc request size 1073741824

Regards,

David

On Thu, 30 Dec 2021 at 23:36, Stephen V. Mather <s...@clevelandmetroparks.com> wrote:

[Shaozhong SHI]

Hi, Steve,

Is there any thing for doing the following:

Start from the source link

Find next link where source link's endnode = startnode of next link

replace the source link with the next link

until no further such connected link exists

Regards,

David

On Thu, 30 Dec 2021 at 23:36, Stephen V. Mather <s...@clevelandmetroparks.com> wrote:

[Shaozhong SHI]

Hi, Steve,

The image does not load.  Where can I find it?  Colleagues of mine want to have a look.

Regards,

David

On Thu, 30 Dec 2021 at 23:36, Stephen V. Mather <s...@clevelandmetroparks.com> wrote: