[Qgis-developer] Questions about symbology: ellipse marker, symbol layer properties, default increment

Marco Hugentobler marco.hugentobler at sourcepole.ch
Wed Jun 20 07:35:58 PDT 2012

Hi Leyan

 >Why is the ellipse marker separated from the simple marker ?

It was the original plan to merge the two approaches, but was never 

Btw., there is an ongoing Google summer of code project about improving 
the symbology system, mentored by Alexander Bruy and Martin Dobias 
(http://www.arunmozhi.in/devlog/june-2012/). Maybe it is of interest for 


Am 17.06.2012 09:29, schrieb 欧阳乐岩:
> Hi all,
> Now that I am confident that bug reports and patches are considered 
> (good response time on the mailing-list by the way !) I started to 
> look a bit more in the code.
> I am currently mostly interested in the symbology code as it is 
> central to my use of QGis and still has a lot of room for improvement 
> in my opinion.
> I have mainly three questions:
> * Why is the ellipse marker separated from the simple marker?
> * What is the logic behind the two level of properties? (global 
> properties for the symbol and then for each symbol layer)
> * Can we change the default values for increment?
> Why is the ellipse marker separated from the simple marker ? Isn't it 
> possible to just replace size by sizeX, sizeY (or keep size and add a 
> ratio if it is judged more intuitive ?) and merge ellipse marker ? 
> Right now, the situation is that both have advantages and drawbacks. 
> Ellipse markers allow to control the outline width (but a 0 width does 
> not work), to use data-defined color, but they do not obey the global 
> color choice (before going into the symbol properties dialog. This 
> means for example that they cannot be used for graduated symbology. 
> They also have less shapes available and cannot be offset like simple 
> symbols.
> Is it a temporary situation and both will develop in different 
> directions later ? Should we merge them ?
> Second, what is the logic behind the symbol layers ? I like the 
> concept as it allows to construct complex symbols easily, but right 
> now the whole thing is a bit shaky: if I make a symbol with two layers 
> using some offset and rotations (real-world use case : a valve symbol 
> by using two triangles touching by one corner), the resulting symbol 
> shape is affected when I manipulate the angle or the size:
> * changing the main rotation will reset all the layers rotation (that 
> was the object of my first patch http://hub.qgis.org/issues/4453)
> * changing the size will scale all layers accordingly and respect 
> their relative size, but the offset will not be modified so elements 
> that were just touching each others will start overlapping.
> Third, is it possible to change the values for increment of line width 
> and border width? I know that when I want to increase a line width 
> from the default 0.26, I very rarely want 1.26, 2.26, 3.26 ... I would 
> love to have 0.26, 0.3, 0.4, 0.5, etc.
> Sorry for the long blurb ! Should I ask someone in particular if I 
> have subsequent questions ?
> Regards,
> Leyan
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Dr. Marco Hugentobler
Sourcepole -  Linux&  Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee

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