[postgis-users] Questions about using SRID not -1
Oscar Zamudio
cmntlk at gmail.com
Thu Jan 21 09:38:07 PST 2010
Hi, me again!
Well at first it cannot be possible to have more than one projection. For
clarity, let explain wht I did to reach at this point:
1- First I created a database 'mydistances' using postgis_template as
template for it.
2-Create a table 'mypoints' with two columns: 'the_name' and "the_geom"
3- Load some GIS data:
INSERT INTO mydistance ( the_geom, the_name ) VALUES (
ST_GeomFromText('POINT(-58.0 0.0)'), 'Punto 1-1');
INSERT INTO mydistance ( the_geom, the_name ) VALUES (
ST_GeomFromText('POINT(-57.0 0.0)'), 'Punto 1-2');
INSERT INTO mydistance ( the_geom, the_name ) VALUES (
ST_GeomFromText('POINT(-58.0 -45.0)'), 'Punto 2-1');
INSERT INTO mydistance ( the_geom, the_name ) VALUES (
ST_GeomFromText('POINT(-57.0 -45.0)'), 'Punto 2-2');
INSERT INTO mydistance ( the_geom, the_name ) VALUES (
ST_GeomFromText('POINT(-58.0 -90.0)'), 'Punto 3-1');
INSERT INTO mydistance ( the_geom, the_name ) VALUES (
ST_GeomFromText('POINT(-57.0 -90.0)'), 'Punto 3-2');
It can be seen there's no SRID indication and that no value is out of the
4326 projection reference.
4- Tried to measure distances between those points usin ST_Distance. As all
those data are in 4326 the retured values are in sexagesimal degrees.
5- Tried to use ST_Transform to UTM projections to get the distances in
meters and all my problems began.
6- I want to get the distances in meters reprojecting the points and not
calculating the meters form the degrees as this calculation depends of the
UTM zone. I know which zone is in each case and there exists the
ST_Transform function so, it is easy to avoid additional external
calculations and obtain directly from the database my results.
7- Tried all the recipes I got from you without success.
Can anybody see what it is the problem with this schema?
On Thu, Jan 21, 2010 at 4:07 AM, ibrahim saricicek <
ibrahimsaricicek at gmail.com> wrote:
> Hi;
>
> No you can change projection any time you want, the point on your table is;
> You have objects in different projections but in one table. You have to
> find which objects are 4326 projection, and which are not...
>
> Another method may be;
>
> Select st_xmin(the_geom), st_ymin(the_geom) from mypoints
>
> if the coordinates differ from -->
>
> Longitude
> 180 W = -180
> 180 E = 180
>
> Latitude
> 90 N = 90
> 90 S = -90
>
> Namely your x not between -180 and 180 and y not between -90 and 90, the
> objects are in an another projection.
>
> I mean firstly try to differ different projected objects..
>
> Regards,
> IBO...
>
>
>
> On Thu, Jan 21, 2010 at 2:01 AM, Oscar Zamudio <cmntlk at gmail.com> wrote:
>
>> Hi,
>> I tried:
>>
>> UPDATE mypoints SET the_geom_4326=transform(the_geom,4326)
>>
>> But again I got:
>>
>> ERROR: Input geometry has unknown (-1) SRID
>>
>> It seems that once the data is without explicit SRID, they cannot
>> be processed later for asigning a proper SRID.
>> It is strange at first sight....but I'm a newbie so I don't know much
>> about this.
>> Regards,
>> Oscar
>>
>> On Tue, Jan 19, 2010 at 6:27 AM, ibrahim saricicek <
>> ibrahimsaricicek at gmail.com> wrote:
>>
>>> Hi,
>>>
>>> Your table include objects, more than one projection.. So if there is any
>>> object in different projection you can't set your table projection to
>>> 4326...
>>>
>>> can you try this!!
>>>
>>> Create a new geometry column "the_geom_4326"
>>>
>>> then run this
>>>
>>> UPDATE table_name SET the_geom_4326=transform(the_geom,4326),
>>>
>>> then use ST_SetSRID for the new column...
>>>
>>> REgards,
>>> ibo...
>>>
>>>
>>> On Mon, Jan 18, 2010 at 7:23 PM, Oscar Zamudio <cmntlk at gmail.com> wrote:
>>>
>>>> Hi everybody.
>>>> I had no success with any of the recipes received here.
>>>> Could it be that a table with data loaded without SRID explicit value
>>>> has no chance of being updated later to the right one?
>>>> Regards,
>>>> Oscar
>>>>
>>>>
>>>> On Sun, Jan 17, 2010 at 1:08 PM, Oscar Zamudio <cmntlk at gmail.com>wrote:
>>>>
>>>>> Ben,
>>>>> I tried your intruction:
>>>>>
>>>>> UPDATE mypoints SET the_geom = ST_SetSRID(the_geom,4326);
>>>>>
>>>>> But I got:
>>>>>
>>>>> ERROR: Operation on two GEOMETRIES with different SRIDs
>>>>>
>>>>> Regards,
>>>>> Oscar
>>>>>
>>>>> On Sat, Jan 16, 2010 at 10:48 PM, Ben Madin <
>>>>> lists at remoteinformation.com.au> wrote:
>>>>>
>>>>>> Oscar,
>>>>>>
>>>>>> you have a couple of options as I see it. In Postgres you could just
>>>>>> update the geometries first.
>>>>>>
>>>>>> > UPDATE mytable SET the_geom = ST_SetSRID(the_geom,4326);
>>>>>>
>>>>>>
>>>>>> And for next time, assuming your data originally had some sort of
>>>>>> coordinate system (and it must have if it was spatial data), you can /
>>>>>> should use the -s flag in shp2pgsql to provide 'SRID awareness'
>>>>>>
>>>>>> In your case, I would suggest -s 4326.
>>>>>>
>>>>>> ie (using -d to drop and replace existing table
>>>>>>
>>>>>> $ shp2pgsql -s 4326 -d myshapefile myoldtablename | psql mydatabase
>>>>>>
>>>>>>
>>>>>> In geometry terms, I think it is unlikely that your data was stored
>>>>>> (spatially) as sexagesimal degrees, although it may be displayed as such in
>>>>>> your GIS.
>>>>>>
>>>>>> cheers
>>>>>>
>>>>>> Ben
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 17/01/2010, at 2:54 , Oscar Zamudio wrote:
>>>>>>
>>>>>> > Hi,
>>>>>> > I'm have problems to transform my spatial data to UTM. First, this
>>>>>> instruction works OK:
>>>>>> >
>>>>>> > SELECT ST_Transform(ST_GeomFromText('POINT(0.0 20)',4326),22171)
>>>>>> from mypoints
>>>>>> >
>>>>>> > No matter if such a sentence has no meaning on what I tryin to do.
>>>>>> But when I did the same with my own points:
>>>>>> >
>>>>>> > SELECT ST_Transform(mypoints.the_geom,22171) from mypoints
>>>>>> >
>>>>>> > I get the following error:
>>>>>> > ERROR: Input geometry has unknown (-1) SRID
>>>>>> > SQL state: XX000
>>>>>> >
>>>>>> > Ok, when I insert my points in my spatial enabled database I used:
>>>>>> >
>>>>>> > INSERT INTO mydistance ( the_geom, the_name ) VALUES (
>>>>>> ST_GeomFromText('POINT(-58.0 0.0)'), 'Punto 1-1');
>>>>>> >
>>>>>> > without no spatial reference system explicit so I guess the SRID is
>>>>>> set to "unknown" i.e. -1. Then naively I created a new column named srid
>>>>>> for my table and put the right value of SRID for all my data which is 4326
>>>>>> (WGS84, sexagesimal degrees lat lon) in that column but still I get the same
>>>>>> error. After that I created a constraint between this new srid column and
>>>>>> the srid column from the spatial_ref_sys table but nothing happened, the
>>>>>> error is still there.
>>>>>> > It's important to me to solve this issue because all my spatial data
>>>>>> was loaded from shapefiles without SRID awareness so they don't have any
>>>>>> SRID column. I don't want to reload data changing this so I need a method to
>>>>>> alter the tables in such a way to add this new srid column to them that is
>>>>>> well related to the spatial context.
>>>>>> > Thanks and regards,
>>>>>> > Oscar
>>>>>> > _______________________________________________
>>>>>> > postgis-users mailing list
>>>>>> > postgis-users at postgis.refractions.net
>>>>>> > http://postgis.refractions.net/mailman/listinfo/postgis-users
>>>>>>
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