[R-sig-Geo] Querying Spatial Data Using rgdal

[Roger Bivand]

On Wed, 12 May 2010, Tim Romel wrote:

> Thanks you both for your quick responses.
>
> Roger, could you please expand on how I would use ogr2ogr with R?  I didn't
> see any direct way to use ogr2ogr within R or to bring the results returned
> by the ogr2ogr command into R spatial objects.

Through system(). Use ogr2ogr to write a temporary file for readOGR() to 
pick up next. Then you can set the -sql or similar selection in the 
ogr2ogr command.

Roger

>
> Thanks again.
>
> On Tue, May 11, 2010 at 6:21 AM, Roger Bivand <Roger.Bivand at nhh.no> wrote:
>
>> On Sat, 8 May 2010, Brooks Kehler wrote:
>>
>>  Have a look at:
>>>
>>> http://www.joeconway.com/plr/
>>>
>>>
>>> http://www.bostongis.com/PrinterFriendly.aspx?content_name=postgresql_plr_tut01
>>>
>>>
>> That only gets you so far. Could Tim please try ogr2ogr with the -sql or
>> -where or -spat arguments set to see whether these go in the correct
>> direction, that is returning geometries meeting the given selection
>> conditions? I have looked briefly at how hard it would be to add this
>> functionality to readOGR(), but without a substantial re-write, it will not
>> be easy. If there are other users who would value such an addition to
>> readOGR, please indicate!
>>
>> Roger
>>
>>
>>
>>>
>>> On Fri, May 7, 2010 at 5:35 PM, Tim Romel <tim.romel at vistracks.com>
>>> wrote:
>>>
>>>  I have the need to bring spatial data into R from a postgres database.  I
>>>> am
>>>> trying to do this right now using rgdal with a command similar to the
>>>> following:
>>>>
>>>> results=readOGR("PG:dbname='dbname' host='hostname' port='portnum'
>>>> user='username' password='pass' <password='P at ssw0rd'>,
>>>> layer="tablename")
>>>>
>>>> This works in bringing back all data from the entire table.  However,
>>>> this
>>>> is a very large table and I was wondering if there was a way to run a
>>>> query
>>>> against the table instead of bringing back all data using readOGR.  I
>>>> have
>>>> found no examples anywhere and have even seen suggestions that it is not
>>>> possible.  Is this the case?  If there are other libraries that support
>>>> R's
>>>> SP library that allow access to postgres that would be great to know too.
>>>>
>>>> Any help is much appreaciated.
>>>>
>>>> Thanks.
>>>>
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>>>>
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>>>>
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>> --
>> Roger Bivand
>> Economic Geography Section, Department of Economics, Norwegian School of
>> Economics and Business Administration, Helleveien 30, N-5045 Bergen,
>> Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
>> e-mail: Roger.Bivand at nhh.no
>>
>>
>

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no