ST_Extent() and ST_Estimated_Extent() return BOX2DFLOAT4s

[mcayland]

In the case of ST_Extent(), this is serious because it means that ST_Extent(col) will never return the exact extent of a column - it will always be inflated by a small amount due to the extra conversion between BOX3D and BOX2DFLOAT4.

• BOX2DFLOAT4s should never be exposed to the user, especially in that

ST_Extent() returns a string containing BOX (a legacy PostgreSQL type) rather than BOX3D *

ST_Estimated_Extent() should also return a string beginning 'BOX3D' for the same reason.

[mcayland]

Fix committed to SVN trunk.

Changing the aggregate function from BOX2DFLOAT4 to BOX3D is the easy part, since the routines already exist for ST_Extent3D(). The hard part is that if we use a box3d to output the extent, then we would change the output from:

BOX(x y, x y)

to:

BOX3D(x y z, x y z)

Since this string is likely parsed by client applications, we need a way to preserve the output format. I've done this by introducing a new SQL type called box3d_extent which is only used by ST_Extent() that uses the same output formats. This is only a temporary hack until we move to the next major version…

ST_Estimated_Extent() we are not too worried about the accuracy since it is based on sampling so I have left this - but when we change the format for ST_Extent() in the future, we should do the same here too.

[colivier]

box3d_extent is not recognize by other Postgis function who already are able to deal with box3d

SELECT ST_Extent('surfaceProperty') FROM 'PrimitiveGeoFeature'; BOX(45.174 30.466,45.891 30.899)

SELECT ST_MAX(ST_Extent('surfaceProperty')) FROM 'PrimitiveGeoFeature'; ERROR: function st_max(box3d_extent) does not exist

SELECT ST_MAX(ST_Extent('surfaceProperty')::box2d) FROM 'PrimitiveGeoFeature'; ERROR: cannot cast type box3d_extent to box2d

[mcayland]

I've just committed the missing casts to trunk as r3938 which should resolve the issue. Please can you test?

ATB,

Mark.

[colivier]

Mark,

On PostgreSQL 8.3.7 postgis.sql load end on error.

⇒box2d function not yet defined in the new cast

I join a patch on postgis.sql.in.c who do the job on my box

And then with you're new cast, that's look good :

SELECT ST_XMAX(ST_Extent('surfaceProperty')::box2d) FROM 'PrimitiveGeoFeature'; 45.8910026550293

SELECT ST_XMAX(ST_Extent('surfaceProperty')) FROM 'PrimitiveGeoFeature'; 45.891

— Olivier

[mcayland]

Ooops - looks like I was using the wrong version of postgis.sql for testing Can you test SVN trunk now?

ATB,

Mark.

[mark.cav...@…]

​http://postgis.googlecode.com/issues/attachment?aid=8004653896858598067&name=DIFF_r3938

[colivier]

Mark, yes it's ok for me now

Olivier