[gdal-dev] gdalsrsinfo supporting files distribution and ogr2ogr usage of OSRFindMatches()

Jorge Gustavo Rocha jgr at osgeopt.pt
Sun Oct 28 17:28:07 PDT 2018


Hi devs,

I've just answered a question related to gdalsrsinfo, to get the fix
#4345 [1].

First question: why these epsg*.wkt.gz files are not distributed with
gdal? Are there any drawbacks?

My second question is about this OSRFindMatches() function. It works
well in gdalsrsinfo. Can it also be used in ogr2ogr?

I was able to identify the correct SRS using gdalsrsinfo, but not when
using ogr2ogr. ogr2ogr assigns the EPSG:900914.

Thanks,

Jorge

[1] https://trac.osgeo.org/gdal/ticket/4345

-------- Mensagem reencaminhada --------
Assunto: Re: [Qgis-user] how does QGIS generate the EPSG from a Shapefile?
Data: Sun, 28 Oct 2018 23:27:48 +0000
De: Jorge Gustavo Rocha <jgr at di.uminho.pt>
Para: qgis-user at lists.osgeo.org

Hi Rodrigo,

GDAL (regular distribution) is not able to identify the EPSG code from
the *.prj string. This is a known limitation. This has been fix (see bug
[1]), but it requires additional files on your side.

Two options:

1) Download the files from:
https://trac.osgeo.org/gdal/raw-attachment/ticket/4345/epsg_ogc.wkt.gz
https://trac.osgeo.org/gdal/raw-attachment/ticket/4345/epsg_ogc_simple.wkt.gz
https://trac.osgeo.org/gdal/raw-attachment/ticket/4345/epsg_esri.wkt.gz

2) You can create the files by yourself running the script
gen_epsg_wkt.sh (available on the #4345 ticket). Change the path to the
existing files. In my GDAL installation, I had to change to:
gcs_epsg=`cat /usr/share/gdal/2.2/gcs.csv | (...)`
pcs_epsg=`cat /usr/share/gdal/2.2/pcs.csv | (...)`

Move/copy the files to your GDAL folder (in my case it is
/usr/share/gdal/2.2)

Then you can use:
gdalsrsinfo -e deinfo_cemiterios.shp

The result will be:

jgr at zoe:~/tmp$ gdalsrsinfo -e deinfo_cemiterios.shp
Warning 1: EPSG detection is experimental and requires new data files
(see bug #4345)

EPSG:29193

PROJ.4 : '+proj=utm +zone=23 +south +ellps=aust_SA
+towgs84=-66.87,4.37,-38.52,0,0,0,0 +units=m +no_defs '

OGC WKT :
PROJCS["SAD69 / UTM zone 23S",
    GEOGCS["SAD69",
        DATUM["South_American_Datum_1969",
            SPHEROID["GRS 1967 Modified",6378160,298.25,
                AUTHORITY["EPSG","7050"]],
            TOWGS84[-66.87,4.37,-38.52,0,0,0,0],
            AUTHORITY["EPSG","6618"]],
        PRIMEM["Greenwich",0,
            AUTHORITY["EPSG","8901"]],
        UNIT["degree",0.0174532925199433,
            AUTHORITY["EPSG","9122"]],
        AUTHORITY["EPSG","4618"]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["latitude_of_origin",0],
    PARAMETER["central_meridian",-45],
    PARAMETER["scale_factor",0.9996],
    PARAMETER["false_easting",500000],
    PARAMETER["false_northing",10000000],
    UNIT["metre",1,
        AUTHORITY["EPSG","9001"]],
    AXIS["Easting",EAST],
    AXIS["Northing",NORTH],
    AUTHORITY["EPSG","29193"]]

Now you can use gdalsrsinfo to identify the CRS. If you need to use this
for scripting, it is easier.

Best regards,

Jorge

[1] https://trac.osgeo.org/gdal/ticket/4345

Às 18:15 de 28/10/18, Rodrigo Mariano escreveu:
> Hello Jorge,
> 
> 
> When I used your command like, the ogr showed this message:
> 
> "Layer name: DEINFO_CEMITERIOS
> Geometry: Polygon
> Feature Count: 42
> Extent: (317568.093609, 7361463.898064) - (357756.090027, 7412287.112520)
> Layer SRS WKT:
> PROJCS["SAD69_UTM_zone_23S",
>     GEOGCS["GCS_SAD69",
>         DATUM["South_American_Datum_1969",
>             SPHEROID["GRS_1967_Modified",6378160,298.25]],
>         PRIMEM["Greenwich",0],
>         UNIT["Degree",0.017453292519943295]],
>     PROJECTION["Transverse_Mercator"],
>     PARAMETER["latitude_of_origin",0],
>     PARAMETER["central_meridian",-45],
>     PARAMETER["scale_factor",0.9996],
>     PARAMETER["false_easting",500000],
>     PARAMETER["false_northing",10000000],
>     UNIT["Meter",1]]
> ID: Integer64 (10.0)
> NOME: String (60.0)
> AREA: Real (20.2)
> DEPADM: String (10.0)"
> 
> When I opened the Shapefile with the QGIS, the software chose the EPSG
> 29193.
> 
> But when I use the ogr2ogr to insert the Shapefile in my database, the
> OGR choose a strange EPSG.
> For that reason, I normally open the Shapefile with the QGIS and I pass
> explicitily the EPSG on ogr2ogr command line.
> Because of that I would like to know how the QGIS discover the EPSG
> given a .prj.
> 
> The .prj of that Shapefile is:
> 
> "PROJCS["SAD69_UTM_zone_23S",GEOGCS["GCS_SAD69",DATUM["D_South_American_1969",SPHEROID["GRS_1967_Truncated",6378160,298.25]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",0],PARAMETER["central_meridian",-45],PARAMETER["scale_factor",0.9996],PARAMETER["false_easting",500000],PARAMETER["false_northing",10000000],UNIT["Meter",1]]"
> 
> 
> Best Regards,
> 
> Rodrigo
> 
> 
> On 25/10/2018 15:59, Jorge Gustavo Rocha wrote:
>> Oi Rodrigo,
>>
>> Can you run ogrinfo in the command line? Like:
>>
>> ogrinfo -al -so yourshape.shp
>>
>> This will tell you the CRS detected by ogr.
>>
>> ogr (and QGIS) uses the *.prj file. But there are known problems with
>> the WKT representation of CRS. Sometimes it is hard to know if two
>> different strings represents the same EPSG code.
>>
>> For that reason, QGIS also writes and additional *.qpj. When it is
>> present, QGIS uses this textual representation to compare it against its
>> database and it always work.
>>
>> But if you just have the *.prj along with the shapefile, both ogr and
>> QGIS might fail to detect the exact CRS.
>>
>> Please share one *.prj that ogr fails to associate with a known EPSG.
>>
>> Abraço,
>>
>> Jorge
>>
>> Às 13:27 de 25/10/18, Rodrigo Mariano escreveu:
>>> Hello everyone,
>>>
>>> I would like to know: how does QGIS generate the EPSG from a Shapefile?
>>>
>>> I ask this question, because I'm trying to upload a Shapefile by OGR,
>>> but the OGR doesn't
>>> insert the correct EPSG. So I need always open the Shapefile in QGIS to
>>> discover the
>>> EPSG before uploading it with OGR.
>>>
>>> Thanks in advance.
>>>
>>> Best Regards,
>>>
>>> Rodrigo
>>>
>>> _______________________________________________
>>> Qgis-user mailing list
>>> Qgis-user at lists.osgeo.org
>>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
>>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
>> J. Gustavo
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J. Gustavo
-- 
Jorge Gustavo Rocha
Departamento de Informática
Universidade do Minho
4710-057 Braga
Tel: +351 253604480
Fax: +351 253604471
Móvel: +351 910333888
skype: nabocudnosor
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