[Gdal-dev] easy ogr question...

[Bryan Keith]

Will, Frank, Dan,

I tested Will's code on a shapefile that had features and received this 
error:

ERROR 6: Can't create fields on a Shapefile layer with features.

Clear enough.

Then I deleted the features from the shapefile, ran the code again, and 
received this error:

ERROR 1: Can't create field test in Shape DBF file, reason unknown.

Not so clear.

Dan, I'm interested in the R code using dbflib because I wrote something 
a while ago in Python using dbflib and my technique was like Will 
described: make a new dbf with an additional field, populate with the 
data from the old one, delete the old dbf and replace it with the new one.

Bryan

Dan Putler wrote:
> Hi Will,
> 
> I add new fields to shapefiles all the time. Although, I do it using  
> R, which (through Frank's shapelib) handles DBFs beautifully. I can  
> provide details, but since this is now off list, I can provide  
> details privately. The main thing is that you only need to muck with  
> the *.dbf file, not the *.shp file itself.
> 
> Dan
> 
> On 19-Sep-06, at 9:33 AM, Will Cadell wrote:
> 
>> Thanks Frank,
>>
>> No message I'm afraid but there are features, and I was wondering how
>> ogr would handle and 'empty' column. I assumed it would add nulls, but
>> hey ho seems like I'll have to make a new shapefile, copy the layer
>> definition then add the field then copy all the features to a new
>> shapefile... Does seem a bit cumbersome though... is there a better  
>> way
>> people can think of?
>>
>> will
>>
>> Frank Warmerdam wrote:
>>> Will Cadell wrote:
>>>> hi guys... am i just stupid or is there another way to add a  
>>>> field to a
>>>> shapefile other than:
>>>>        ds = ogr.open("c:\shapefile.shp", True)
>>>>        new_field = ogr.FieldDefn()
>>>>     new_field.SetName(new_field_name)
>>>>     new_field.SetType(new_field_type)
>>>>     new_field.SetWidth(new_field_width)
>>>>        layer = ds.GetLayer(0)
>>>>     layer.CreateField(new_field)
>>>>        ds.destroy
>>>>
>>>> because this doesn't work for me...
>>> Will,
>>>
>>> This does seem like the correct approach.  Are there any features  
>>> in the
>>> shapefile already?  I'm pretty sure that adding a field only works  
>>> when
>>> there are no features yet.  If you aren't getting an error message  
>>> then
>>> there is a clear bug here, and a bug report in bugzilla would be
>>> appreciated.
>>>
>>> Best regards,
>> -- 
>> Will Cadell
>> Remote Sensing and GIS Analyst
>>
>>    /\/\
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