[postgis-users] What's the Purpose of the Geometry_Columns Table?

[TECHER David]

Stephen Frost a écrit :

>* Paul Ramsey (pramsey at refractions.net) wrote:
>  
>
>>Yes, that is correct, GEOMETRY_COLUMNS is for the outside world.  It  
>>would be nice if it could transparently auto-update as things happen  
>>in SQL land, but we have not yet found a way to make that happen,  
>>despite years of wanting it to.
>>    
>>
>
>I'm very interested in finding a way to make it transparent.  I'm
>not entirely sure how everything fits together though.  I'd also like to
>have it moved out of the 'public' schema and into someplace more
>appropriate, though I'm not sure what impact that would have on the
>applications which use it.
>
>At first glance it looks like the geometry_columns could be based off
>the pg_class, pg_attribute, and pg_type system tables by just looking
>for tables which have columns of type 'geometry'.  I see that
>geometry_columns also contains the number of dimensions, the srid, and
>the type.  Are all three needed? 
>
Yes they are! Make a error with mapserver from a postgis connection and
U will see why U need this!

Make a postgis connection with the same data but with different srids!
and so on...

There are lost of examples to see why we need these infos!


> Can any of them be pulled from the
>table directly?  Would they perhaps make more sense as individual types
>instead of having just the one 'geometry' type?
>
>I especially wonder about the last as the values in those columns appear
>to be enforced through check constraints generally anyway...  Perhaps
>what we need is an easy way to define new types and some appropriate
>casting functions for them instead of attempting to munge all the,
>apparently distinct, types into one.
>
>	Thanks,
>
>		Stephen
>  
>
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