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

欧阳乐岩 ouyang.leyan at hotmail.com
Sun Jun 17 00:29:20 PDT 2012

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 

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 ?



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