[postgis] 'real' contains, touches, overlaps etc.

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[postgis] 'real' contains, touches, overlaps etc.

Manuel Weindorf
Hi,

Fist I have to say that I love PostGIS VERY much, I was working with
PostgreSQL for a while using it's geometry type but the possibilities
provided now are much more promising.

One question:
Is somebody actually working on the following operators ???
contain(g1,g2)
touches(g1,g2)
overlaps(g1,g2)

These functions are important for me (at least concerning the polygon type),
and so I just started implementing them (based on the postgis-cvs version).
I don't know how far I get but, if there's another one doing the same, please
let me know (because of the reinvented wheels ;-)

ciao,
Manuel

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Re: [postgis] 'real' contains, touches, overlaps etc.

David Blasby-3
> One question:
> Is somebody actually working on the following operators ???
> contain(g1,g2)
> touches(g1,g2)
> overlaps(g1,g2)

We're waiting for the JTS (java topology suite) with is a robust
implementation of a bunch of operators and function, including the
above.  JTS is scheduled to be released in Sept, but it needs to be
translated to C++ before it can go in postgis.

> These functions are important for me (at least concerning the polygon type),
> and so I just started implementing them (based on the postgis-cvs version).
> I don't know how far I get but, if there's another one doing the same, please
> let me know (because of the reinvented wheels ;-)

Go for it!  You might want to look at the distance functions for a
starting place.  There is also the truely_inside() function.

dave

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Re: [postgis] 'real' contains, touches, overlaps etc.

Manuel Weindorf
On Tuesday 28 August 2001 18:17, you wrote:

> > One question:
> > Is somebody actually working on the following operators ???
> > contain(g1,g2)
> > touches(g1,g2)
> > overlaps(g1,g2)
>
> We're waiting for the JTS (java topology suite) with is a robust
> implementation of a bunch of operators and function, including the
> above.  JTS is scheduled to be released in Sept, but it needs to be
> translated to C++ before it can go in postgis.
>
> > These functions are important for me (at least concerning the polygon
> > type), and so I just started implementing them (based on the postgis-cvs
> > version). I don't know how far I get but, if there's another one doing
> > the same, please let me know (because of the reinvented wheels ;-)
>
> Go for it!  You might want to look at the distance functions for a
> starting place.  There is also the truely_inside() function.
>
> dave
>

Hi,

today I implemented the contains and the overlaps function (it was not so
hard while using the PIP stuff already there. I test it for a while and send
you the code soon (If you want it ;-) ...

But I recognized one thing:

The PIP test does just divide between two cases -> inside and outside
One problem (concerning to OGC conformity) is that we need a on-boundary
operator to implelement touches(g1,g2) and the others in the coorect way.

I'm thinking about that (maybe I should wait, but I need it before ..)

bye
Manuel
--

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Re: [postgis] 'real' contains, touches, overlaps etc.

David Blasby-3
> today I implemented the contains and the overlaps function (it was not so
> hard while using the PIP stuff already there. I test it for a while and send
> you the code soon (If you want it ;-) ...

Yes - send it in and I'll add it.  I'm looking forward to it.
 
> But I recognized one thing:
>
> The PIP test does just divide between two cases -> inside and outside
> One problem (concerning to OGC conformity) is that we need a on-boundary
> operator to implelement touches(g1,g2) and the others in the coorect way.
>
> I'm thinking about that (maybe I should wait, but I need it before ..)

Yes, there's lots of research into robust sign of determinates.
Basically, if you can do that, you can robustly answer the question:
"does this point lies to the left, to the right, or on this line?"

Its very difficult to find out if a point is on a line or not because
the precision of the calculations (and the actual numbers) in the
computer are not exact.

dave

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