[postgis-users] Compare SQL Server 2008 Spatial, PostGIS, MySQL functionality

[Paragon]

Actually I'm all confused about how the geography thing works.  I always
thought you would just stuff 4326 in there and it would just use an
elliptical model.  Reading further it seems you can use any valid spatial
ref and measurements are always in meters.  But then the Books OnLine are
especially confusing because it seems to suggest you can only use
ST_Distance between a point and another geography type which would make it
just a tad bit better than the Postgis distance spheroid functions.  The
SRIDs also apparently need to match.  I think we'll need to test this one
out since I'm still unclear what exactly it does with the SRID.  Seems to me
it would only need it for loading data.

Below is the BOL documentation on ST_Distance for geography

STDistance() always returns null if the spatial reference IDs (SRIDs) of the
geography instances do not match.

Distance can only be determined between a point and another geography
instance. This method will return null if at least one of the instances is
not a point. 

In addition, if STDistance() is used to determine distance between antipodal
points, or consecutive points on opposite sides of the globe, as in the
distance between POINT (0 0) and POINT (180 0), this method will return
null.



-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Richard
Greenwood
Sent: Thursday, July 17, 2008 10:53 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Compare SQL Server 2008 Spatial, PostGIS,MySQL
functionality

On Thu, Jul 17, 2008 at 5:55 PM, Paragon <lr at pcorp.us> wrote:
> As part of our due diligence work, we are formulating a comparison of 
> the spatial functionality offered by SQL Server 2008 Spatial, PostGIS and
MySQL.
> Its currently in draft, but we hope to release within the next week.
>
> We would appreciate if people could take a quick look at it and let us 
> know if you see any gross errors or important things we left out.  
> Most of this information we curled from reading the help docs of each 
> product and from our general familiarity with the databases and GIS 
> products out there.  We tried to be as fair as possible.
>
>
> http://www.bostongis.com/PrinterFriendly.aspx?content_name=sqlserver20
> 08_pos
> tgis_mysql_compare
>
> Thanks,
> Regina and Leo

Nice work. I'm confused in the Spatial Functionality matrix, SQL Server 08
Geography Transformations, you have:
"Not relevant, does hold of originating source and SRID must be defined in
sys.spatial_reference_systems"
Why isn't that relevant? You should be able to transform between datums, no?

--
Richard Greenwood
richard.greenwood at gmail.com
www.greenwoodmap.com
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