[postgis-devel] rebuild_bbox_caches.pl (was: URGENT BUGFIX)

[strk at refractions.net]

Never-on-vacation hackers,

I've spent some time producing a script to recompute all bounding
box caches in a spatial database.

I tought it was due before an 1.0.3 release, so dump/reload
can still be avoided. 

If you want to help fighting dump/reload requirements please
test the script on your test databases.

It is a perl script under utils/ of the pgis_1_0 branch
of CVS.

It will update every geometry columns, reindex and
analyze every spatial table.

I didn't test the script against pre 7.4 postgresql databases,
any test there is highly appreciated.

Thank you.

--strk;


On Tue, Jul 26, 2005 at 12:22:20AM +0200, strk at refractions.net wrote:
> Thanks to Miguel de la Fuente I've found and killed a severe
> bug in bounding box computation.
> 
> EVERY BOUNDING BOX computed by postgis 1.x and cached in
> the geometry value is possibly CORRUPTED.
> 
> The corruption is due to a precision reduction which could
> make the cached bounding box smaller then the associated geometry.
> 
> This example shows the problem:
> 
>   query: SELECT box2d(GeomFromText('MULTIPOINT(5256301.4  6014563.13)'));
>  result: BOX(5256301.5 6014563,5256301.5 6014563)
> 
> As you can see the box is horizontally contained-in the multipoint.
> 
> Not all geometry constructors are affected, but many.
> GeometryFromText() is an exellent positive.
> 
> Version 1.0.3 will be out soon for a fix.
> A patch is attached.
> 
> NOTE that a simple library-only upgrade WILL NOT fix the cached
> bounding boxes.
> 
> To fix cached bounding boxes you should either dump/reload your db
> OR select addbbox(dropbbox(g)) on EVERY geometry column of EVERY spatial
> table, REINDEX every spatial index and run vacuum analyze or
> select geometry_stats() depending on pgsql version.
> 
> --strk;

> Index: lwgeom/ptarray.c
> ===================================================================
> RCS file: /home/cvs/postgis/postgis/lwgeom/ptarray.c,v
> retrieving revision 1.15
> diff -U2 -r1.15 ptarray.c
> --- lwgeom/ptarray.c	9 Jun 2005 16:01:22 -0000	1.15
> +++ lwgeom/ptarray.c	25 Jul 2005 22:19:42 -0000
> @@ -126,4 +126,5 @@
>  	int t;
>  	POINT2D pt;
> +	BOX3D box;
>  
>  	if (pa->npoints == 0) return 0;
> @@ -131,18 +132,20 @@
>  	getPoint2d_p(pa, 0, &pt);
>  
> -	result->xmin = pt.x;
> -	result->xmax = pt.x;
> -	result->ymin = pt.y;
> -	result->ymax = pt.y;
> +	box.xmin = pt.x;
> +	box.xmax = pt.x;
> +	box.ymin = pt.y;
> +	box.ymax = pt.y;
>  
>  	for (t=1; t<pa->npoints; t++)
>  	{
>  		getPoint2d_p(pa, t, &pt);
> -		if (pt.x < result->xmin) result->xmin = pt.x;
> -		if (pt.y < result->ymin) result->ymin = pt.y;
> -		if (pt.x > result->xmax) result->xmax = pt.x;
> -		if (pt.y > result->ymax) result->ymax = pt.y;
> +		if (pt.x < box.xmin) box.xmin = pt.x;
> +		if (pt.y < box.ymin) box.ymin = pt.y;
> +		if (pt.x > box.xmax) box.xmax = pt.x;
> +		if (pt.y > box.ymax) box.ymax = pt.y;
>  	}
>  
> +	box3d_to_box2df_p(&box, result);
> +
>  	return 1;
>  }

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