Re: PostGIS

Hi All ..

Please forgive my ignorance ....
After all it is open source ...so how can one trust it fully ....
I am GIS guy (i think ..)

Like We have used the Haversine formula ...given on most of the websites ...
to calculate the distance between to lat/lon points ..

which doesnt match with the distance given by distance_sphere() method
...!!!

How can I convice my boss .who doesnt know abt gis leave ..Postgis that
Postgis is correct and not is Formula ...

Thanks
Sandeep
PS:- Actually i am a big fan of opensource GIS stuff ...

On 10/31/06, Bent Wood <b(dot)wood(at)niwa(dot)co(dot)nz> wrote:
>
> Sandeep Kumar Jakkaraju wrote:
> >
> > I use postgis to wipe my ASS ...
> > no good documentation ...
>
> The docs are a bit technical, but the product is excellent, I use it to
> manage a variety of spatial datasets, with up to hundreds of millions of
> features, on half a dozen systems. I'd highly recommend it, & would also
> say that the online support from the developers and users is of a very
> high standard.
>
> Note that you should have some sort of understanding of projections
> before you start doing things like measuring or reprojecting, to
> understand the issues involved, but these are not just a Postgis issue.
>
> In answer to the original question (I'd have replied earlier but just
> got back from 2 weeks at sea - using Postgis amongst other things)
> If you look at the case studies Paul Ramsey is accumulating at
> http://postgis.refractions.net/news/ it might help.
>
>
> > in what units is the result of distance(geometry,geometry)
>
> As in the docs, the distance is returned in the units specified in the
> projection definition of your geometries.
>
> > what is distance_sphere(geometry,geometry).. when u give same geometry
> > as both parameters it gives a non-zero value ....
> Hmm. just tried this. Within floating point rounding errors, this seems
> to contradict this claim, unless you suggest a floating point non-zero
> represenation of zero is a postgis error. In which case I suggest
> CompSci 101 might be educational.
>
> corax=# select distance_sphere(the_geom,the_geom) from bivouac_pnt limit
> 10;
> distance_sphere
> ----------------------
> 0
> 0
> 0
> 0
> 0
> 7.07321632848846e-10
> 7.07321632848846e-10
> 7.07321632848846e-10
> 0
> 7.07321632848846e-10
> (10 rows)
>
>
>
> Cheers,
>
> Brent Wood
>
>
> >
> > On 10/19/06, *James Cradock* <jcradock(at)me3(dot)com
> > <mailto:jcradock(at)me3(dot)com>> wrote:
> >
> > On Oct 19, 2006, at 11:08 AM, Bob Pawley wrote:
> >
> >> Can anyone point me to an overview of PostGIS and how it is being
> >> used???
> >
> > Bob,
> >
> > PostGIS provides extensions to PostgreSQL's procedural language
> > and geometric data types so that it can store geo-referenced data,
> > and so that you can query this data using geo-spatial coordinates.
> >
> > Software like MapServer (web) and Qgis (desktop) use PostGIS to
> > provide data in map applications.
> >
> > The Refractions site already noted is a good start. The MapServer
> > site is another:
> >
> > http://mapserver.gis.umn.edu/gallery
> >
> > Jim
> >
> > -----
> >
> > James Cradock, jcradock(at)me3(dot)com <mailto:jcradock(at)me3(dot)com>
> >
> >
> >
> >
> >
> > --
> > Sandeep Kumar Jakkaraju
> > WeBlog:
> > http://jakkarajus.blogspot.com
>
>
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--
Sandeep Kumar Jakkaraju
WeBlog:
http://jakkarajus.blogspot.com