[postgis-devel] Is there a reason those GArray functions aren'tdocumented?

[Obe, Regina]

Kevin,

----------------
> I think this is exactly why they were never documented.  I suppose we 
> could add an "Internals" section to the documentation and catalog
these 
> as well as all the _ST* methods.


> I think this, or the simliar approach 
> ST_MakePolygon(ST_MakeLine(geometry set)), is how one would build up a

> Polygon - construct linestrings that define the exterior and interior 
> rings, and use them to define the boundary of the polygon.

> Cheers,
> Kevin

Thanks. Agreed these should probably be in a separate section if we have
them at all.  In this particular case I couldn't use geometry set
because a geometry set requires rows of data where as I had a finite set
of points  constructed by separate operations against a known geometry.
Think of a complex geometry where you want to create a new geometry from
select properties of that geometry e.g. the exterior, the 5th interior
and the 6th interior (well thats not a good example).  

You would have to resort to something silly and inefficient but granted
more SQL portable like

SELECT B.*,
ST_Polygonize(ST_Collect(B.the_geom))

FROM 
(
UNION ALL SELECT A.otherfields, some_monkey_business_adding_some
points(ST_Exterior_Ring(the_geom)) 
FROM A
UNION ALL SELECT A.otherfield, some_other_monkey_business(A.the_geom) 
... FROM A

... the unions can get pretty ugly after a while) ) B ..
GROUP BY ...


When you could have done more (maybe not more simply) but I suspect more
efficiently

SELECT A....,
ST_Polygonize_garray(ARRAY[some_monkey_business_adding_some
points(ST_ExteriorRing(the_geom)),
some_other_monkey_business(ST_ExteriorRingN(the_geom,2))]) As the_geom

FROM  A

So I finally got fed up and just used one of those garray functions.

Its a rare use case but it does lurk its ugly head every once in a while
and then I have to wash myself off after using it because I felt dirty
using a non-documented PostGIS function and also a particular unique
feature of PostgreSQL (its implementation of arrays) :).

Thanks,
Regina
 

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