[Qgis-developer] Virtual columns in QGIS, was: Re: [Qgis-user] object labels

[kimaidou]

Hi

Since I have not tested your patch yet, it is hard to comment. The
functionnalities I am thinking of for labelling purpose are :
* be able to add uppercase to the first letters of words
* add a line break after the first space after X letters (such as Mapserver
does with WRAP and MAXLENGTH ( http://mapserver.org/mapfile/label.html )
* Concatenate one or more columns with expresssions, such as : colA || '('
|| colB || ')'   (here I am using the postgresql || syntaxe )

kimaidou


2011/7/28 Nathan Woodrow <madmanwoo at gmail.com>

> +1 from me too.  A virtual column would be a very handy feature however you
> must be able to add one to read only datasets eg MI Tab otherwise their is
> no real advantage.  The expression labelling I'm working on works with read
> only datasets.   I think the expression based labelling and the virtual
> column thing could exist together quite well the former being a short cut in
> the labeling gui for the latter.
>
> Check out http://hub.qgis.org/issues/3488 and
> https://github.com/NathanW2/Quantum-GIS/tree/expression-labels for the
> status of my patch.  I have been away for a couple of weeks but I will be
> getting back into over the next couple of weeks.
>
> Anyone else got any other thoughts?
>
> - Nathan
>
> On Thu, Jul 28, 2011 at 6:49 PM, kimaidou <kimaidou at gmail.com> wrote:
>
>> Hi,
>>
>> +1 for Mayeul Nathan. This "virtual column" would be a very handy tool !
>> E.G for labelling
>>
>> kimaidou
>>
>>
>> 2011/7/28 Andreas Neumann <a.neumann at carto.net>
>>
>>> Hi Nathan,
>>>
>>> Good to hear that you are working on this.
>>>
>>> I just wonder if it wouldn't make sense to have a general purpose
>>> "virtual column" that could be introduced in QGIS. This would be useful for:
>>>
>>> * labeling
>>> * map tips/QGIS server tooltip display
>>> * symbology
>>> * plugins
>>> * others?
>>>
>>> It would be convenient to use the field calculator, but instead of just
>>> writing out to a physically existing column it would create a new virtual
>>> column, just like a virtual column in a database view.
>>>
>>> Otherwise one would have to develop the same functionality several times
>>> - for labeling, for tooltips, etc.
>>>
>>> Do you think it would be feasible to implement this on a lower level in
>>> QGIS so that users could transparently work with virtual columns wherever
>>> they want?
>>>
>>> Andreas
>>>
>>> On Thu, 28 Jul 2011 16:09:56 +1000, Nathan Woodrow wrote:
>>>
>>>> My upcoming patch that adds expression based labels will be able
>>>> to achieve this once it's completed;  I'm just cleaning up the UI
>>>> and testing everything then I will get the guys to merge it in.
>>>>  Until then you will need to create a new column.
>>>>
>>>> - Nathan
>>>>
>>>> On Wed, Jul 27, 2011 at 9:15 PM, Torsten Lange  wrote:
>>>>
>>>>  Ok, thank you, Andreas!
>>>>>
>>>>> Torsten
>>>>>
>>>>> Am Mittwoch 27 Juli 2011, 11:00:01 schrieb Andreas Neumann:
>>>>>
>>>>>   Hi,
>>>>>>
>>>>> >
>>>>> >  Currently, you have to create a new column. I usually create a
>>>>> view in
>>>>> >  Postgis for this purpose.
>>>>> >
>>>>> >  It is in on the wishlist that one can create a "virtual" column
>>>>> - not
>>>>> >  only for labeling, but also for map tips and perhaps
>>>>> symbolization.
>>>>> >  Until then you have to do it yourself.
>>>>> >
>>>>> >  Andreas
>>>>> >
>>>>> >  On Tue, 26 Jul 2011 22:51:34 +0200, Torsten Lange wrote:
>>>>> > > Hi,
>>>>> > >
>>>>> > > Is there a way just to print - lets say - the first four
>>>>> letters of a
>>>>> > > objects
>>>>> > > name? Or must I create a new row for that?
>>>>> > >
>>>>> > > Thank you, Torsten
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>>>>
>>>>
>>>>
>>>> Links:
>>>> ------
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>>>> [5] mailto:tlange at gwdg.de
>>>>
>>>
>>> --
>>> --
>>> Andreas Neumann
>>> Böschacherstrasse 10A
>>> 8624 Grüt (Gossau ZH)
>>> Switzerland
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>>
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