[postgis-users] Precision of the bounding box query

[Alexander Ulanov]

Thank you, this was really helpful!



2013/9/2 Mike Toews <mwtoews at gmail.com>

> On 2 September 2013 18:10, Alexander Ulanov <avulanov at gmail.com> wrote:
> > Does this mean that all bounding box queries have to be written with
> casting
> > to geometry type? Bounding box originates from the browser with google
> maps.
>
> I suppose so, as long as the map used to base the BBOX queries share
> the same grid orientation as a lat/long grid (not the case for UTM,
> LCC and others, but true for Mercator projections). To get a good idea
> of a straight line for the geography type you have to see it on a
> globe (or something like Google Earth), but never on a flat map.
>
> > Related question. Do I really need geography type for my locations if my
> > queries are only bounding box and st_dwithin ?
>
> Geography types are still really handy for ST_DWithin, since they use
> nice linear metric units for distances. So I guess it depends how much
> you use this function or other distance-based functions. There are
> also several ways to get metric area and distance values from geometry
> data of long/lat too. Be sure to read the relevant manual section [1]
> to help you decide.
>
> [1]
> http://postgis.net/docs/using_postgis_dbmanagement.html#PostGIS_Geography
>
> -Mike
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