[postgis-devel] ST_Npoints vs. ST_NumPoints

[Mark Cave-Ayland]

Paragon Corporation wrote:

> I thought we were going to change ST_NumPoints to be an alias for
> ST_Npoints.  Doesn't look like we have as of 1.4
> 
> Anyrate there is one thing I am noticing disturbing about ST_NumPoints.  It
> appears that for MULTILINESTRINGS it returns the number of points of only
> the first line string.  Is that by design?
> 
> SELECT atype, ST_NPoints(the_geom) As npoints, ST_NumPoints(the_geom) As
> numpoints
> FROM (VALUES ('a line m ' , ST_GeomFromEWKT('LINESTRINGM(1 2 3, 3 4 5, 5 8
> 7, 6 10 11)') ) ,
>  ('a circular string' ,  ST_GeomFromText('CIRCULARSTRING(2.5 2.5,4.5 2.5,
> 4.5 4.5)') ) ,
> ('A triangle', ST_GeomFromText('POLYGON((0 1,1 -1,-1 -1,0 1))')  ),
> ('a multilinestring', ST_GeomFromText('MULTILINESTRING ((1 2, 3 4, 5 6), (10
> 20, 30 40))') ),
> ('A collection', ST_Collect(ST_GeomFromText('POLYGON((0 1,1 -1,-1 -1,0
> 1))'), ST_Point(1,3)) )
> )
> As foo(atype,the_geom);
> 
> 
> Gives:
> 
>        atype       | npoints | numpoints
> -------------------+---------+-----------
>  a line m          |       4 |         4
>  a circular string |       3 |
>  A triangle        |       4 |
>  a multilinestring |       5 |         3
>  A collection      |       5 |
> 
> Thanks,
> Regina

Hmmm that smells like a bug to me. What does spec say about 
ST_NPoints()/ST_NumPoints() and its behaviour for MULTI types? I'd 
imagine only one of these is the "official"  function for counting 
points within a geometry.


ATB,

Mark.

-- 
Mark Cave-Ayland - Senior Technical Architect
PostgreSQL - PostGIS
Sirius Corporation plc - control through freedom
http://www.siriusit.co.uk
t: +44 870 608 0063