[Qgis-user] Send us your tips!

[Martin Dobias]

On Wed, Mar 2, 2011 at 9:56 AM, Tim Sutton <lists at linfiniti.com> wrote:
> Hi Martin
>
> On Wed, Mar 2, 2011 at 10:48 AM, Martin Dobias <wonder.sk at gmail.com> wrote:
>> On Wed, Mar 2, 2011 at 12:25 AM, Alister Hood
>> <alister.hood at synergine.com> wrote:
>>> But I think symbol levels should probably be enabled by
>>> default, in which case this tip wouldn't be necessary :)
>>
>> Rendering with symbol levels is more costly, so -1 for me to enable it
>> by default.
>>
>
> I remember debating this with you at Wroclaw. Is it more costly also
> in situations where symbols are simple and have 1 layer each only? In
> the case of multilayer symbols I would say 99% of the time I want
> symbol levels on. I do quite a lot of training and the symbol levels
> is something that a) new users struggle to comprehend and b) gets
> forgotten as a detail after the training and then people come back to
> me asking why their maps look funny. I think from a user friendliness
> point of view, there would be a lot gained by enabling it by default
> (performance issues notwithstanding). Maybe we should add it as
> another item in our endless options panel (which I will reorganise in
> Lisbon)?

Hi Tim

yes, it's more costly also for symbols with just one symbol layer. The
idea is that the features in current view are loaded into memory first
(with a reference to symbol that will be used) and then rendered. So
there is some memory overhead and some cpu overhead (unsure about the
total amount). The case with just one symbol layer could be probably
optimized to some degree.

I am not sure what to do here. The concept of symbol level is quite
advanced and becomes more complex when drawing things like highway
crossing (I still haven't found time to write a blog post explaining
how that could be done). Maybe another topic for upcoming hackfest?
:-)

Martin