1

I am working through the book 'pgRouting: A Practical Guide' and have come across a function that has been deprecated. The function is pgr_pointToEdgeNode. Is there a similar function I can use to convert a point to a vertex_id based on closest edge?

This is a link to the function from version 2.1.0.

2

In case not (have you checked the docs?), use a simple (K)NN search:

SELECT CASE WHEN ST_LineLocatePoint(geom, <point>) < 0.5
         THEN source
         ELSE target
       END as node
FROM   edges
ORDER BY
       geom <-> <point>
LIMIT   1
;

ST_LineLocatePoint in the CASE finds the fraction of line length of the projected point from <point> on the closest edge.geom, and selects either source or target.

A spatial index on edges is mandatory.


You can outsource the <point> creation into a CTE if you want.

You could also wrap this up in a function, but note that for a batch solution on a table of points (or more than one point) you'd better CROSS JOIN LATERAL the points table/expression to a (K)NN subquery. See e.g.

| improve this answer | |
  • Yes I checked the docs for pgr. I read through most of the manual and couldn't find any information about the pgr_pointToEdgeNode or a replacement for it. I know KNN search and this function was basically a wrapper for that search. I was hoping there was something similar in the latest version of pgr. I suppose I will create my own function using something similar to your answer. Another method using the pgr vertices table is SELECT id FROM ospr.ways_vertices_pgr ORDER BY the_geom <-> ST_SetSRID( ST_Point(-77.009003, 38.889931), 4326) limit 1 – jbalk May 18 at 20:17
  • I guess that function predates some major improvements to the <-> operator that aren't easily implemented in an extension. But that's only a guess. Writing a function for one point is fine, better use the inline SQL solution for batch searches. Note that you may get different results with your alternative, as a vertex may be closer to point even if the point is right next to an edge. – geozelot May 18 at 20:24
  • That makes sense. You are correct, your example should provide the best results. What makes me curious is why this function was deprecated. I thought features were usually deprecated because their functionality was replaced by a different function. I assumed this was the case with this function but I could not find any similar functions in pgr. Maybe I'm missing something. – jbalk May 18 at 21:23
  • The function was deprecated to reduce the number of functions that need to be maintained and documented. A few functions made it into pgRouting over the years that didn't bring much value, so it was decided to focus on the core functionality. – dkastl May 18 at 23:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.