[postgis-devel] EMPTY
Paragon Corporation
lr at pcorp.us
Tue Oct 6 20:14:23 PDT 2009
Martin,
As much as I prefer FFF.FFF.FFF for presentation. I think it would be
confusing since the more OGC compliant ST_Relate expects FFFFFFFFF for
input. So having the input of one function not be the output of another to
me is even more confusing an annoying.
Also I tested this in SQL Server 2008 and it returns 0. So I take it SQL
Serve disagrees?
SELECT Geometry::STGeomFromText('POLYGON
EMPTY',4326).STRelate(Geometry::STGeomFromText('POLYGON EMPTY',4326),
'FFFFFFFFF') => 0
For PostGIS the operation is unsupported for geometry collections I guess
because GEOS doesn't support it so can't compare.
What is interesting is that this resolves to 1 and I would have expected 0?
SELECT Geometry::STGeomFromText('POLYGON
EMPTY',4326).STEquals(Geometry::STGeomFromText('POLYGON EMPTY',4326)) => 1
Which seems puzzling to me because I thought equality requires intersection
by OGC standards. If that's the case -- SQL Server has violated its model
because
SELECT Geometry::STGeomFromText('POLYGON
EMPTY',4326).STRelate(Geometry::STGeomFromText('POLYGON EMPTY',4326),
'T*F**FFF*') => 0 (the intersection matrix for equality)
Or they are defining STEquals in a way I am unfamiliar with. Maybe their
STEquals is binary equality.
Thanks,
Regina
-----Original Message-----
From: postgis-devel-bounces at postgis.refractions.net
[mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of Martin
Davis
Sent: Tuesday, October 06, 2009 5:31 PM
To: PostGIS Development Discussion
Subject: Re: [postgis-devel] EMPTY
Yes, I replied too soon - after I realized that ST_relate returns the
matrix,not a boolean result.
But yes, I think FFFFFFFFF is the most reasonable return value.
BTW, I'm thinking of changing JTS so that it returns a more readable format
for the pattern - eg FFF.FFF.FFF (recognized where I got that idea?)
BTW2, the PG doc for ST_relate looks a little confusing to me. It lists the
ST_relate methods in the order (2 args => text, 3 args ==> boolean), but
then goes on to say "Version 1 returns BOOLEAN....)
Paul Ramsey wrote:
> Meaning FFFFFFFFF ? :)
>
> On Tue, Oct 6, 2009 at 2:25 PM, Martin Davis <mbdavis at refractions.net>
wrote:
>
>> FALSE!!!!
>>
>> Paul Ramsey wrote:
>>
>>> OK, the uber question (Kevin can meditate over this one tonight):
>>>
>>> ST_Relate(geometry, empty)
>>> ST_Relate(empty, empty)
>>>
>>> :)
>>>
>>> On Tue, Oct 6, 2009 at 2:11 PM, Paragon Corporation <lr at pcorp.us> wrote:
>>>
>>>
>>>> Yap 0 on all counts. Wow those Microsoft people are really smart.
>>>>
>>>> --geometry contains empty
>>>> SELECT Geometry::STGeomFromText('POINT(1
>>>> 2)',4326).STContains(Geometry::STGeomFromText('POLYGON EMPTY',4326))
>>>> => 0
>>>>
>>>> --geometry within empty
>>>> SELECT Geometry::STGeomFromText('POINT(1
>>>> 2)',4326).STWithin(Geometry::STGeomFromText('POLYGON EMPTY',4326))
>>>> => 0
>>>>
>>>> --empty contains geometry
>>>> SELECT Geometry::STGeomFromText('POLYGON
>>>> EMPTY',4326).STContains(Geometry::STGeomFromText('POINT(1
>>>> 2)',4326)) => 0
>>>>
>>>> --empty within geometry
>>>> SELECT Geometry::STGeomFromText('POLYGON
>>>> EMPTY',4326).STWithin(Geometry::STGeomFromText('POINT(1 2)',4326))
>>>> => 0
>>>>
>>>> Thanks,
>>>> Regina
>>>>
>>>> -----Original Message-----
>>>> From: postgis-devel-bounces at postgis.refractions.net
>>>> [mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf Of
>>>> Chris Hodgson
>>>> Sent: Tuesday, October 06, 2009 5:03 PM
>>>> To: PostGIS Development Discussion
>>>> Subject: Re: [postgis-devel] EMPTY
>>>>
>>>> I agree with you Regina, and I bet SQL Server does too.
>>>>
>>>> Chris
>>>>
>>>> Paragon Corporation wrote:
>>>>
>>>>
>>>>> They should all be false.
>>>>>
>>>>> Isn't the first requirement of containment/contains be that the
>>>>> two geometries intersect -- so if we say empty can't intersect
>>>>> with anything including empty, how can anything possibly contain it?
>>>>>
>>>>> Though have to pull out my sql server 2008 to see if it is in
agreement.
>>>>>
>>>>> Thanks,
>>>>> Regina
>>>>>
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>> From: postgis-devel-bounces at postgis.refractions.net
>>>>> [mailto:postgis-devel-bounces at postgis.refractions.net] On Behalf
>>>>> Of Paul Ramsey
>>>>> Sent: Tuesday, October 06, 2009 4:39 PM
>>>>> To: PostGIS Development Discussion
>>>>> Subject: Re: [postgis-devel] EMPTY
>>>>>
>>>>> In the spirit of maintaining the geometry logical flow, what do
>>>>> you think of these ideas?
>>>>>
>>>>> * ST_Contains(geometry, empty) == TRUE
>>>>> * ST_Within(geometry, empty) == FALSE
>>>>> * ST_Contains(empty, geometry) == FALSE
>>>>> * ST_Within(empty, geometry) == TRUE
>>>>>
>>>>> What does SQL Server say?
>>>>>
>>>>> P
>>>>>
>>>>> On Tue, Oct 6, 2009 at 1:34 PM, Paul Ramsey
>>>>> <pramsey at cleverelephant.ca>
>>>>> wrote:
>>>>>
>>>>>
>>>>>
>>>>>> I'm going to change my intersection/disjoint answers to agree w/
>>>>>> SQL Server. They are not bad, and they maintain the symmetry
>>>>>> between where intersection => ! disjoint.
>>>>>>
>>>>>> P.
>>>>>>
>>>>>> On Tue, Oct 6, 2009 at 12:45 PM, Chris Hodgson
>>>>>> <chodgson at refractions.net>
>>>>>>
>>>>>>
>>>>>>
>>>>> wrote:
>>>>>
>>>>>
>>>>>
>>>>>>> I moved these and summarized the interesting results from SQL
>>>>>>> Server
>>>>>>> 2008 next to your original lines Paul.
>>>>>>>
>>>>>>> Note that SQL Server says that everything is disjoint from
>>>>>>> empty, including empty itself - whereas your original guesses
>>>>>>> were to return
>>>>>>>
>>>>>>>
>>>>>>>
>>>>> false.
>>>>>
>>>>>
>>>>>
>>>>>>> So far I think I like SQL Server's answers. Would be good to
>>>>>>> compare with oracle spatial too.
>>>>>>>
>>>>>>> Chris
>>>>>>>
>>>>>>> Paul Ramsey wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>> Regina, could you move your SQL Server examples down to a big
>>>>>>>> block at the end, so the main part of the document is more
>>>>>>>> readable? So far I agree with SQL Server in all the examples!
>>>>>>>> Those guys are smart! :)
>>>>>>>>
>>>>>>>> P
>>>>>>>>
>>>>>>>> On Tue, Oct 6, 2009 at 12:12 PM, Paul Ramsey
>>>>>>>> <pramsey at cleverelephant.ca>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>> On Tue, Oct 6, 2009 at 12:03 PM, Chris Hodgson
>>>>>>>>> <chodgson at refractions.net>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> I would dare say that geometry empty is more like zero, than
null.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>> Bingo, there's a useful mental model. Wikify that!
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>> _______________________________________________
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>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
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>>>>>>>
>>>>>>>
>>>>>>>
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>> --
>> Martin Davis
>> Senior Technical Architect
>> Refractions Research, Inc.
>> (250) 383-3022
>>
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--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
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