[postgis-devel] Geog/Geom Hack

[Paragon Corporation]

Paul,
Hmm when I am comparing distance of two geometries in different spatial refs
which I do a lot.

I still don't like the hack even if you disregard the above or if you must
hack -- don't give it the same name as the non-hacked functions.

the whole idea of picking BestSRID for a person to cater to less technical
users I find extremely annoying as I can think of 20 "BestSRID" depending on
what I am doing.  If they get to that level of sophistication, I would
rather have them think a little more  and understand the implications of
those decisions.

We must learn to crawl before we can learn to walk,because walking without
understanding will just get you into trouble in the long run.


 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: Friday, October 30, 2009 9:47 PM
To: PostGIS Development Discussion
Subject: Re: [postgis-devel] Geog/Geom Hack

You *can*, but I strongly doubt you *will*. Because there's nothing in
geography that isn't already in geometry. So you as a primary geometry user
are going to have no working need to cast things to geography.

On the other hand, the very first question from users of geography will be
"how can I access <geometry function N>?" So having a relatively full set of
functions already available in geography makes sense to me, even if they are
hacked in with a planar trick.

P.

On Fri, Oct 30, 2009 at 5:46 PM, Paragon Corporation <lr at pcorp.us> wrote:
> Paul,
> I can put a functional geography index on can't I and take advantage 
> of geography index bindings?
>
> Lets say I have a large network of tables broken out by region so I 
> know a specific table has one srid.
>
> For many queries, I may go to that table directly or if I'm doing 
> single geometry processing, really don't care what srid as long as its 
> in utm or whatever - so I can use the full power of GEOS.
>
> For my across the board distance checks and so forth, I would want to 
> use geography and I could use a geography index if I put a functional 
> geography index on my geometry correct?  Though that needs some more
testing.
>
>
> So in short if 90% of my workload involves geometry processing, I will 
> want to keep my data in geometry
>
> But the 10% I would want to convert to geography on the fly.
>
> 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: Friday, October 30, 2009 8:34 PM
> To: PostGIS Development Discussion
> Subject: Re: [postgis-devel] Geog/Geom Hack
>
> I'm not sure I understand why you would ever convert a geometry to a 
> geography as part of a query on a geometry table. I fully expect 
> geography to be used as a storage type, because of the utility of 
> having the correct spherical indexes, which are not available when 
> you're just converting in via a cast. Since there's no functions 
> available on geography that are not already available on geometry, why 
> would you ever do a geometry->geography cast unless you are (a) 
> testing geography or (b) bulk converting a table into geography for
storage in that type.
>
> P.
>
>
>
> On Fri, Oct 30, 2009 at 5:24 PM, Paragon Corporation <lr at pcorp.us> wrote:
>> Paul,
>> I would rather you didn't for 2 reasons
>>
>> 1) I'm lazy and for each of these things we'd have to apply the text 
>> additional function proto hack to prevent from it breaking geometry.
>> which we will probably end up taking out anyway.
>>
>> 2) I don't like the hiddenness of it since it becomes especially 
>> annoying if you have your native in geometry and you are converting 
>> to geography for a special usecase, then you end up with a slower 
>> implementation
>>
>> as you would really end up doing accidentally
>>
>> geometry -> geography -> geometry ->operation (and why do I want my 
>> calcs done in UTM?)
>>
>> Instead of the more efficient
>>
>> geometry -> operation
>>
>> 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: Friday, October 30, 2009 8:16 PM
>> To: PostGIS Development Discussion
>> Subject: [postgis-devel] Geog/Geom Hack
>>
>> I'm interested to know what the general opinion is of the trick I've 
>> used on
>> ST_Buffer(geography):
>>
>> http://trac.osgeo.org/postgis/browser/trunk/postgis/geography.sql.in.
>> c
>> #L541
>>
>> I ask because I could apply the same idea to the larger suite of OGC 
>> SFSQL predicates before release. Is half-a-loaf better than no loaf 
>> in
> this case?
>> (Note that there will be failure cases for really large geometry, 
>> like a polygon of "Asia" or "Russia" that have polygons over the 
>> dateline.)
>>
>> P.
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