Hi Paul, Thanks for looking into it.
On Tue, Jul 3, 2018 at 11:41 PM, Paul Ramsey <[email protected]> wrote: > > When I look at what we do for geometry: > > select st_astext(st_expand('LINESTRING(0 0, 1 1)'::geometry, 1)); > > POLYGON((-1 -1,-1 2,2 2,2 -1,-1 -1)) > > Huh, we morph a linestring into a polygon, odd, right? But it's a > polygon that represents the bounds. > That makes sense in theory, though I admit I don't fully understand how a line segment gets expanded to a polygon of that shape. Naively I would have expected that each point on the polygon boundary to be at a distance of 1 unit from the line segment. But I remember only a few things from my geometry class :-) > > I start to think that perhaps the existing behavior is broken, and > geography expand should rewrite the object so that it becomes > something that has the 3-space bounds we want. Maybe an appropriately > chosen multipoint, for example. It will be very confusing to people, > though, since they tend to think rectangularly about bounds, even when > working with spherical coordinates, which are very decidedly not > rectangular. > Its a relief that you think that the existing behaviour is broken, otherwise I would have to look for ugly hacks in XL to fix this. But even outside XL, I think this could be a problem for PostGIS since a SQL expression may get evaluated, then converted into a string representation and later converted back into the in-memory representation, losing critical information on the way. So I think it's appropriate that we fix this in PostGIS. Would it be feasible to output the bounding box information in geography_out() and reconstructed back in the geography_in() function? Thanks, Pavan P.S. Paul, I've distinct memories from your keynote at PGCon 2011, which I'd immensely liked. I did not get chance to congratulate you then, so here I am doing so after 7 years ;-) -- Pavan Deolasee http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
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