[postgis-users] Geography/geometry

[Simon (SPDBA) Greener]

I'm didn't load into geometry, I used ogr2ogr to load into geography. All work to date has been ok except now I want to aggregate union the polygon parts of bounties with multiple polygon parts. ST_Union is not geographic aware hence all the trouble.

Using geometry as the load target does not appear to help me because of the geodetic vs projected linestring issue. 

There are other situations eg ST_Wdithin, that return incorrect results when points fall on boundaries (I had to hack a solution to get correct within results for geographic data.)

I don't my just do the processing for Ireland but also Australia and the USA, the common factor being 4326. So the solution has to be geography not geometry.

Well for as much as I understand all these things?

PS I need a common framework when training across PostGIS, SQL Server Spatial and Oracle Spatial. I also want the math to be correct for the geography data, as it should.

Regards
Simon


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On 22 Jan. 2019, 09:41, at 09:41, Paul Ramsey <pramsey at cleverelephant.ca> wrote:
>
>
>> On Jan 21, 2019, at 1:46 PM, Simon Greener
><simon at spatialdbadvisor.com> wrote:
>> 
>> Thanks Paul.
>> 
>> However, I get the same number of distinct st_isvalidreason results.
>
>Something is awry here, because I get only 'Valid Geometry’ as a
>validity check result… I loaded your shape file, I have 42 irish
>counties, I didn’t even try to use geography, just used geometry and
>they are all valid to start with.
>
>I can even push them through a couple casts and they remain valid (as I
>would hope they would, since the coordinates shouldn’t change) 
>
>select distinct st_isvalidreason(geom::geography::geometry) from
>county;
>
>P
>
>> 
>> Is there anything I can do with ogr2ogr when loading to help?
>> 
>> Simon
>> 
>> On Tue, 22 Jan 2019 08:34:02 +1100, Paul Ramsey
><pramsey at cleverelephant.ca> wrote:
>> 
>>> +proj=gnom +lat_0=53.35 +lon_0=-6.26 +x_0=0 +y_0=0 +ellps=WGS84
>+units=m +no_defs
>> 
>> 
>> -- 
>> Regards
>> Simon
>>
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