[Qgis-developer] Data-defined symbol size is not backwards compatible to 2.8.2

[Vincent Mora]

Hi Andreas,

On 02/06/2015 16:07, Andreas Neumann wrote:
> I found another issue with the new scaling method:
>
> For multi level point symbols we need to be able to define the scaling
> on the symbol level. However, when adding it on the symbol level, the
> same rule applies both on the parent marker and on the individual
> symbol level.
>
> What if one part of the symbol should be scaled differently than the
> other? We really need this to work on the indivual symbol levels, not
> on the parent marker - or at least make it optional that it scales the
> parent as well.

The marker size/rotation expression don' not actually exists, like the
marker size/rotation.

You can define different size/rotation expressions at the symbol level.
Each symbol can have it's own variation.

It's only in the particular case where the scale/rotation expressions of
all symbols composing a marker preserve the aspect ratio of the symbol
that it is recognized as a marker expression and displayed as such.


>
> As it works currently, I get a very different rendering in the map,
> compared to the preview in the legend ;-(
>
Can you file a bug repport for this if it's not fixed by
https://github.com/qgis/QGIS/pull/2111 ?

Thanks,

V.
> Andreas
>
> On 02.06.2015 15:53, Andreas Neumann wrote:
>> Hi,
>>
>> Thanks for explaining. The assistant is very nice and a welcome
>> improvement! Thanks for investing and working on it.
>>
>> I had an issue that I had a size defined in 2.8.x with "scaling by
>> area" which, when opened in QGIS master displayed much bigger. Once I
>> changed that in 2.8x to "scale by diameter" the symbol sizes are
>> identical in master.
>>
>> So there seems to be an issue with converting "scale by area" symbol
>> sizes from 2.8 over to QGIS master.
>>
>> Should I open a bug report or is one open already?
>>
>> Thanks,
>> Andreas
>>
>> On 01.06.2015 20:05, Régis Haubourg wrote:
>>> Hi,
>>> here are the ideas behind this work, Nyall (code reviewer) and Vincent
>>> (author) could explain implentation choices more than me (funder):
>>>
>>> - get a more consistent UI with data defined widgets, and not "advanced
>>> fields". That way, size is in one place only.
>>> - offer an assistant on size varying common expression. You will
>>> find it at
>>> the bottom of the drop down widget. It computes max value from field or
>>> expression and allows normal user to do what other GIS do.
>>> - That assistant offer legend previsualisation, and generates a
>>> legend for
>>> map and composer. I wish we have a legend for any expression...
>>> - During implementation, we understood that symbol size was a
>>> multiplication
>>> factor of size varying factor. That implied that it was impossible to
>>> predict final screen size. The new implementation clears that up.
>>> - offer a size varying graduated renderer, allowing the use of
>>> classifications algorithms
>>> - offer a legend for diagrams (yes!)
>>>
>>> IMHO, we need to read previous versions correctly, but that
>>> sometimes need
>>> to read all features to retroengineer a size expression. Vincent have
>>> planned to polish that now that feature freeze is made.
>>>
>>> All that needs testing of course. I'm not totally satisfied with the
>>> assistant shortcut, hidden inside the size varying widget. If
>>> someone have a
>>> better UI idea..
>>>
>>> Hope that helps clarifying those changes.
>>> Cheers
>>> Régis
>>>
>>>
>>>
>>>
>>>
>>> -- 
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