[pgrouting-users] Create network with nodes at least every 50m

[Ian Tangert]

Also, there has been work on queries using pgr_drivingDistance that will
return partial edges if the next node is not within the distance.  These
functions will return all the segments you want and then you could use
st_convexHull to get a polygon of the catchment area.

https://github.com/GregersP/networkReach

https://github.com/iant1212/networkReach


On Sat, Aug 23, 2014 at 10:31 PM, Stephen Woodbridge <
woodbri at swoodbridge.com> wrote:

> Hi Adam,
>
> ST_Segmentize returns a multilinestring and pgrouting does not know what
> to do with them so it takes only the first segment and ignores the rest.
>
>  http://postgis.refractions.net/docs/ST_Segmentize.html
>
> You will need to explode the into multiple linestrings. look at
>
>  http://postgis.refractions.net/docs/ST_Dump.html
>
> for how to do that.
>
> What you probably should do is something like:
>
> 1. create a new edge table
> 2. process all you edges with segmentize and dump into the new table
> 3. then run pgr_createTopology on the new table
> 4. then try to route against the new table
>
> -Steve
>
>
> On 8/23/2014 8:16 PM, Adam Lawrence wrote:
>
>> Hi,
>>
>> I have spent over a week trying to work this out. I have an existing
>> road network and have used pgr_alphashape to try and get a 400m walking
>> catchment from bus stops.
>>
>> But pgr_alphashape snapes to the nearest network node which means
>> catchments returned are significantly smaller than 400m. I have
>> therefore tried to create a new network with nodes every 50m using
>> ST_Segmentize but I can't seem to get it to work.
>>
>> The function below is my attempt to loop through the existing network
>> and run ST_Segmentize on each entry to return updated network with
>> additional nodes but it only returns one record each time rather than a
>> number of segmented entries.
>>
>> Any advice on how to make this work or alternative approach would be
>> greately appreciated (especially given that following over a week and
>> research it seems no one else has had this problem).
>>
>> Regards
>> Adam
>>
>>
>>
>>
>> DROP FUNCTION hutt_pax.my_test_function();
>> CREATE OR REPLACE FUNCTION hutt_pax.my_test_function()
>>    RETURNS TABLE (
>> xid integer,
>> xgeog geometry) AS
>> $BODY$
>> DECLARE
>>      r hutt_pax.roads_wainuiomata%ROWTYPE;
>> BEGIN
>> FOR r IN
>> SELECT *
>> FROM hutt_pax.roads_wainuiomata
>> LOOP
>>
>> xid := r.id <http://r.id>;
>>
>> xgeog := ST_Segmentize(
>> r.geom,
>> 0.050
>> );
>>
>> RETURN NEXT;
>> END LOOP;
>>
>> RETURN NEXT;    -- return final result
>>
>> END;
>> $BODY$ LANGUAGE plpgsql STABLE;
>>
>> SELECT *
>> FROM hutt_pax.my_test_function();
>>
>>
>>
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>>
>>
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