[postgis-users] Questions about using SRID not -1
Oscar Zamudio
cmntlk at gmail.com
Thu Jan 21 11:08:51 PST 2010
I already stated that this is only an experiment trying to solve the problem
because my customer already loaded a lot of data WITHOUT expliciting SRID
reference..... I mean,
INSERT INTO mydistance (the_geom, the_name) VALUES
(ST_GeomFromText('POINT(-58.0 0.0)',4326),'Punto 1-1');
Is a step without SRID value that was taken years ago on their database. I'm
trying to avoid the reloading process and taking in account that there are
some functions that probably can make the task,,, I began to explore them
without success up to now.
Regards,
On Thu, Jan 21, 2010 at 3:55 PM, Chris Hermansen <
chris.hermansen at timberline.ca> wrote:
> Oscar;
>
> Read this:
>
>
> http://www.postgis.org/documentation/manual-1.4/ch04.html#Create_Spatial_Table
>
> Note the use of the AddGeometryColumn() to put a geometry column on your
> table and put an entry in the geometry_columns table, including setting the
> SRID correctly.
>
> So your example might be
>
> CREATE TABLE mydistance (the_name text);
> SELECT AddGeometryColumn('mydistance','the_geom',4326,'POINT',2);
> INSERT INTO mydistance (the_geom, the_name) VALUES
> (ST_GeomFromText('POINT(-58.0 0.0)',4326),'Punto 1-1');
>
> etc assuming you wanted SRID 4326.
>
> The next section tells you how to manually register a geometry column if
> you have created it manually.
>
> Oscar Zamudio wrote:
>
>> Hi, Two things. First, the name of the table in the INSERTS sentences is
>> 'mypoints', not 'mydistance'. Second: I tried what Ibrahim suggested:
>>
>> Select st_xmin(the_geom), st_ymin(the_geom) from mypoints
>>
>>
>> And the results are:
>>
>> -58;0
>>
>> -57;0
>>
>> -58;-45
>>
>> -57;-45
>>
>> -58;-90
>>
>> -57;-90
>>
>>
>> So, none of them (as was expected) is out of the geometry projection
>> reference.
>>
>>
>> On Thu, Jan 21, 2010 at 2:38 PM, Oscar Zamudio <cmntlk at gmail.com <mailto:
>> cmntlk at gmail.com>> wrote:
>>
>> 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 <mailto: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 <mailto: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
>> <mailto: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 <mailto: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 <mailto: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
>> <mailto: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
>> >
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>
> --
> Regards,
>
> Chris Hermansen · chris.hermansen at timberline.ca · skype:clhermansen
> tel+1.604.714.2878 · fax+1.604.733.0631 · mob+1.778.840.4625
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