[Qgis-developer] Vienna hackfest: QGIS Legend discussion

[HAUBOURG]

Hi again,

> -----Message d'origine-----
> De : Martin Dobias [mailto:wonder.sk at gmail.com]
> Envoyé : mercredi 2 avril 2014 13:15
> À : HAUBOURG
> Cc : qgis-dev
> Objet : Re: [Qgis-developer] Vienna hackfest: QGIS Legend discussion
> 
> Hi Régis
> 
> On Wed, Apr 2, 2014 at 11:55 AM, Régis Haubourg <regis.haubourg at eau-
> adour-garonne.fr> wrote:
> >>
> >> This is not part of the refactoring work, but it is very interesting
> >> use case and therefore I will keep it in mind and do the design in a
> >> manner that adding such functionality should be possible. Advanced
> >> legend manipulation could be another followup project.
> >
> > Hi Martin, does that mean that we need to wait that your refactoring
> > is finished before starting a work on proportionnal legends? What is
> > the target version for that?
> 
> The refactoring is a requirement for such thing - the goal of that work is
> really to allow greater flexibility of legend widget. The plan is to get it into
> 2.4 release.
[RH] OK, that is sufficient for me, but I will ask other state services we are trying to coordinate if an higher urgency is there.

> 
> > This is a high priority use case here, should we fund a temporary
> > plugin for current versions ? This is sub-optimal too me, and that
> > requires also we fund first a plugin, and secondly a core feature.
> 
> Unfortunately I do not think it would be possible to have a plugin that would
> show the proportional legend directly in legend widget or composer legend.
> Maybe a plugin that would just generate an image with proportional legend
> so it could be included in composition - not a great solution.
> 
> I can imagine a python plugin for QGIS >=2.4 that would add this
> functionality.
[RH] Yes, as Gino says, generating an image is a bad solution. We might be just consolidating LegendSVG plugin if urgency is there. 

> 
> 
> >> - legend vs layer manager - there was a good point that we are mixing
> >> the concept of map legend and layer manager into one tree. While
> >> these are related, they get into conflicts... while layer manager
> >> should be a tool for management of the map (and be as powerful as
> >> possible), map legend should provide mainly the help for the user to
> >> identify the map elements (and be as simple as possible).
> >
> > Are you heading to an arcmap like solution with different tabs in
> > layer registry?
[RH] 
Don't you have a licence ;-) ? See here [0] what esri calls as dataframe. This is a meta layer group. Only one is activated in mapcanvas. But when user switch to composer view (in the same window, just a small button in status toolbar), then each map object of the composer is a different dataframe. This is much nicer than having to play with "lock layers" checkbox and mapcanvas status. I see users here tends to have one layer group for each map object in multimap composers.. so we're not so far from a user point of view. We just need that new meta layer group.. Of course, that's much more complicated in API.
> 
> I'm not really sure what you mean... maybe a screenshot would help.
> 
> 
> Regards
> Martin

[RH] Concerning the basic requirements for proportional legends, that's what we have in mind:

- minimal support of proportional symbol sizes in layer registry for point symbols and lines, we just need here 3 symbols with a size + values of these symbols . see [2]
- functional size symbol only  for simple symbols composed of 1 marker: 
	- graduated , categorized and ruled base renderer using no data defined setting. 
	- data defined point size or line width and current advanced proportion field (to be merged with data defined settings see [1]). This use case is more tricky, since we have to read actual data to generate some legend, and we need some user input to choose min and max size and values for legend symbols. See Mapinfo gui [3]. Middle symbol can be generated using active expression, user shouldn't have to take care of this.  
- support for  cleaner legends in composer. We can imagine different layouts and have more classes in legend. See [4]

[0] http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//006600000004000000
[1] http://osgeo-org.1560.x6.nabble.com/Duplication-of-functionality-Data-defined-size-and-Size-scale-field-td5131007.html#a5131122
[2] https://dl.dropboxusercontent.com/u/72368800/arcmap_prop_symbol3.png
[3] https://dl.dropboxusercontent.com/u/72368800/mapinfo_proportionnal_symbols.png
[4] https://dl.dropboxusercontent.com/u/72368800/possible_proportionnal_symbols_legends.png