[mapserver-users] PostGIS layer projection

[Jeff McKenna]

Hi Radim,

Here is a working mapfile reprojecting a PostGIS layer: 
https://github.com/mapserver/mapserver/wiki/Reproject-PostGIS-Layer

You ask good questions, that could likely just be tested by checking the 
postgres logs and executing the raw commands from those logs at the psql 
commandline and comparing.

As you go down this path, please do add to that new wiki page with your 
own notes :)

-jeff



-- 
Jeff McKenna
MapServer Consulting and Training Services
https://gatewaygeomatics.com/



On 2019-07-18 8:04 AM, Radim Blazek wrote:
> Hi Jeff,
> thanks, yes I have read that.
> 
> But I also read that  "using srid= is optional but improves
> performance" so there was a little chance that re-projection could be
> done anyway if a different SRID is found on geometry.
> 
> If there is no further transformation, what difference "using srid="
> does? What happens if SRID is not set on column and there are mixed
> geoms' SRIDs.
> 
> I mean, where is CRS transformation done if request CRS != layer CRS
> != column CRS? I would expect calling directly PostGIS
> ST_Transform(geom, request_srid), which would by pass
> LAYER.PROJECTION.
> 
> Radim
> 
> On Thu, Jul 18, 2019 at 12:31 PM Jeff McKenna
> <jmckenna at gatewaygeomatics.com> wrote:
>>
>> Hi Radim,
>>
>> Give the Projection document a good read specifically the "Important
>> Notes" section which I believe answers your questions:
>> https://mapserver.org/mapfile/projection.html#important-notes
>>
>> There are no specific driver rules; for something like a PostGIS
>> connection you should be able to follow the "Important Notes" above.
>> MapServer will assume that you have configured the driver properly (in
>> the case of PostGIS, setting the SRID as well, since PostGIS requires
>> that parameter to do a projection)
>>
>> -jeff
>>
>>
>> --
>> Jeff McKenna
>> MapServer Consulting and Training Services
>> https://gatewaygeomatics.com/
>>
>>
>>
>> On 2019-07-18 5:59 AM, Radim Blazek wrote:
>>> Hi,
>>> can you please explain how does re-projection of PostGIS layers work?
>>> If there is a POSTGIS layer with DATA without "using srid=" but
>>> PostGIS column has SRID defined, there is constraint for that SRID on
>>> the column and geometries have SRID set, is it necessary to define
>>> PROJECTION for that layer if SRID of the column is different from that
>>> of mapfile?
>>>
>>> For example, geometry column has SRID=4326, geometries have SRID set, mapfile:
>>>
>>> NAME test
>>>        PROJECTION
>>>            "init=epsg:3857"
>>>        END
>>>        LAYER test
>>>             CONNECTIONTYPE postgis
>>>             DATA "geo FROM test"
>>>        END
>>> END
>>>
>>> if a request comes to render a map in 3857, will be geometries
>>> re-projected correctly from 4326 to 3857?
>>>