[postgis-users] [postgis-devel] Sphere or Spheroid

[pcreso at pcreso.com]

My 02c, 

The simplest invocation generates the simplest/fastest result. A more complex invocation (specifying spheroid) generates a more accurate/complex/slower result.

I'm not sure I really understand the question, as a query:
ST_distance(g,g) returns a sphere based result, while 
ST_distance(g,g,spheroid) returns an spheroidal result.

I think my preferred approach for this would be;

If users can pre-set a default spheroid to use, then ST_distance(g,g) is still spherical, but ST_distance(g,g,'default') uses the selected default spheroid, otherwise the spheroid must be specified explicitly.

So a spheroidal calculation is only applied when a spheroid is explicitly supplied in the function, otherwise use a spherical calculation.


Cheers,

  Brent Wood


--- On Sat, 10/31/09, Paragon Corporation <lr at pcorp.us> wrote:

> From: Paragon Corporation <lr at pcorp.us>
> Subject: Re: [postgis-users] [postgis-devel] Sphere or Spheroid
> To: "'PostGIS Development Discussion'" <postgis-devel at postgis.refractions.net>, "'PostGIS Users Discussion'" <postgis-users at postgis.refractions.net>
> Date: Saturday, October 31, 2009, 12:48 PM
>  
> The choice of default sphere vs. spheroid is probably
> something we should
> ask the general PostGIS users group so cc'ing them since
> more people
> frequent that list that would have strong opinions on this
> subject.
> 
> So question folks -- is which do you prefer as default
> behavior for new
> geography data type
> 
> faster sphere calculation (with 0.05% - 1% margin error) (I
> vaguely recall
> that's what my studies suggested around the globe compared
> to UTM)
> 
> or 
> slower more accurate spheroid calculation
> 
> Keep in mind -- this is just default behavior without an
> extra arg to the
> functions, you can use both in your work.

<snip>