[mapserver-dev] Re: [gdal-dev] Padding/spacing in mysql driver
output
Even Rouault
even.rouault at mines-paris.org
Tue Apr 21 14:34:43 EDT 2009
CC'ing mapserver-dev as it is one potential place where this behaviour could
be changed.
After discussing this subject with Frank, it appears that the left padding was
added so that column oriented reports would line up nicely.
We are a bit shy to change this behaviour now in GDAL as some applications may
rely on it for pretty formatting.
For your use case, one solution would be to do the stripping in mapserver
itself (in mapogr.cpp). Currently it calls the OGR_F_GetFieldAsString(),
which is the function that adds the left padding for numeric fields with a
non zero width. A solution would be that mapserver checks the type of the
field, and if it is numeric (OFT_Integer or OFT_Real), it removes any leading
whitespace.
Le Sunday 19 April 2009 11:39:49 P.Romero, vous avez écrit :
> "If you look at the first lines of your ogrinfo dump, you'll see that the
> fields with left padding are declared in the form :
> lat: Real(22.0)"
>
> - Where is this information? I didn’t see it; How can I access it?
>
> "One possible workaround is that you change your MySQL table definitions so
> that the columns are not of the form double(x,y) but just double."
>
> - AFAIK, I never set a precision value for double fields when the tables
> were created; they were created simply as 'double'. I'll need to
> double-check this, but I honestly don’t believe that I set the precision;
> perhaps MySQL defaults to '22' as the field size for doubles? I'll need to
> look into this. Im hoping that I will, in fact, be able to adjust this
> within MySQL...
>
> I cant see any usefulness in this behavior; perhaps it would be worth
> considering as a 'feature request' to eliminate this extra spacing in a
> future release?
>
> Thanks again for the help,
> P.Romero
> -----Original Message-----
> From: Even Rouault [mailto:even.rouault at mines-paris.org]
> Sent: 2009-04-19 4:24 AM
> To: gdal-dev at lists.osgeo.org
> Cc: P.Romero; Frank Warmerdam
> Subject: Re: [gdal-dev] Padding/spacing in mysql driver output
>
> Hi,
>
> this behaviour is not specific to the MySQL driver. When a field has a
> specified width and precision, it will get formatted according to it. This
> behaviour was specifically introduced 10 years ago ! :
> http://trac.osgeo.org/gdal/changeset/745. So it looks like a behaviour by
> design, although I'm not clear on its justification. Maybe Frank will
> remember ?
>
> If you look at the first lines of your ogrinfo dump, you'll see that the
> fields with left padding are declared in the form :
> lat: Real(22.0)
>
> One possible workaround is that you change your MySQL table definitions so
> that the columns are not of the form double(x,y) but just double.
>
> Another one, quite inelegant and possibly not performing well, is to embed
> the content of your ovf file into another ovf file and use the CAST
> operator of OGR SQL (see http://gdal.org/ogr/ogr_sql.html)
>
> For example:
>
> <OGRVRTDataSource>
> <OGRVRTLayer name="poly">
> <SrcDataSource> <!-- here put your original OVF file, but
> XML-escaped -->
> <OGRVRTDataSource>
> <OGRVRTLayer name="poly">
> <SrcDataSource>MYSQL:even</SrcDataSource>
> <SrcSQL>SELECT area FROM poly</SrcSQL>
> </OGRVRTLayer>
> </OGRVRTDataSource>
> </SrcDataSource>
> <!-- here cast every double field as float(1) -->
> <SrcSQL>SELECT CAST(area as float(1)) FROM poly</SrcSQL>
> </OGRVRTLayer>
> </OGRVRTDataSource>
>
> Best regards,
> Even
>
> Le Sunday 19 April 2009 09:32:31 P.Romero, vous avez écrit :
> > Hi,
> > Im new to this list.
> > I use ogr w/ the mysql driver as part of a mapserver installation.
> >
> > Im having an issue with the formatting of numeric results that are
> > being returned from a mysql query.
> > It appears that values originating from 'double'-typed fields in the
> > MySQL database are showing up in ogr's output with a large amount of
> > 'blank space' left-padding.
> >
> > Here's an example of some output from running "ogrinfo -al
> > 'myQueryFile.ovf'":
> >
> > OGRFeature(mypoints):86
> > max(recTS) (Integer) = 1240078380
> > buoyName (String) = 51202
> > lat (Real) = 21
> > lon (Real) = -158
> > MAG (Real) = -371
> > WDIR (Real) = -99
> > WSPD (Real) = -99
> > ADIR (Real) = 81
> > ts (DateTime) = 2009/04/04 0:43:00
> > POINT (-157.680000000000007 21.420000000000002 0)
> >
> > In case my hotmail account mangles the above output, here is a
> > description of what is occuring:
> > Any value with a datatype of 'Real' (i.e., 'double' in MySQL) is
> > appearing with approx. 20 spaces of left-padding. However, other
> > datatypes are not showing this large padding.
> >
> > The extra spacing is also showing up in my mapserver ogr/mysql query
> > output; its unnecessary, unwanted, & unacceptable, so Id like to remove
>
> it.
>
> > Is this spacing a bug, or by design?
> > How can I go about removing it from ogr's query results?
> >
> > Thanks in advance,
> > P.Romero
> >
> > _______________________________________________
> > gdal-dev mailing list
> > gdal-dev at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/gdal-dev
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