[postgis-devel] RC5 problem

[Carl Anderson]

strk at refractions.net wrote:

>On Sat, Mar 26, 2005 at 05:34:46PM -0500, Carl Anderson wrote:
>  
>
>>possibly too late in the development cycle for this discussion.
>>    
>>
>
>Indeed.
>
>I was not trying to convince you.
>I do see the problem, but I was giving you more information.
>The solution you suggest is a non-solution as a box2d::box3d
>cast doesn't give you more precision. The precision issue
>is not related to output but internal representation:
>
>=# select xmin('POINT(1.0000000001 0)'::geometry::box3d);
> 1.0000000001
>=# select xmin('POINT(1.0000000001 0)'::geometry::box3d::box2d);
>    1
>=# select xmin('POINT(1.0000000001 0)'::geometry::box3d::box2d::box3d);
>    1
>
>The first call is the only one giving you full precision.
>
>The question here is if we really want to keep support for BOX3D
>for other then just an input type support (implicitly casting
>to box2d for any operation, for example).
>
>--strk;
>  
>

but the behavior demonstrated is the same in the present and my pondered 
states
(I pondered renaming xmin(box2d) to xmin2d(box2d), and leaving xmin(box3d) )
passing through box2d will reduce precision, as a feature of the box2d 
type no
matter what the precision of the desination type will be.

xmin(box3d) uses   BOX3D_xmin
xmin(box2d)  casts box2d into box3d and flows into BOX3D_xmin
xmin(box3d::box2d::box3d) casts box3d into box2d casted into box3d and 
flows into BOX3D_xmin

I believe the default should be to have more precision and reduced 
precision should be explicit
requests.  As you demonstrated you can't add precision after removing it.

I yield to your judgement, and thank you for your consideration.

C.