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

[Martin Dobias]

Hi Leyan

On Sun, Jun 17, 2012 at 9:29 AM, 欧阳乐岩 <ouyang.leyan at hotmail.com> wrote:
>
> I have mainly three questions:
> * Why is the ellipse marker separated from the simple marker?

Marco has answered this - ideally they should be merged to one class.

> * What is the logic behind the two level of properties? (global properties
> for the symbol and then for each symbol layer)

"global" symbol properties are common for all layers: setting symbol's
size/angle/color will modify that property for all symbol layers.
There are various options that can be set only at the level of each
symbol layer.

> * Can we change the default values for increment?

Yes, where that would be appropriate.


> 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 ?

We should definitely 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)

I see that your patch has been applied already...

> * 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.

That's something that should be fixed, too... a patch to fix that
would be welcome.


> 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.

Yes, that could be changed, too.


> Sorry for the long blurb ! Should I ask someone in particular if I have
> subsequent questions ?

This mailing list is the best place to ask such questions: people
involved into the project follow it and answer if they have answers
and time :-)

Regards
Martin