[Qgis-user] Rule based styles using SVG markers

[Patrick Dunford]

Good day to all.

I have noted in my projects repeated issues relating to the use of SVG 
symbols as part of specific line-based styles. Currently some of my 
line-based styles have an SVG symbol overlaid on top of a particular line.

When these styles are stored into the style manager and exported from 
there to a styles file there seems to be little difficulty for the 
software in being able to reload the SVG symbols from the file when 
software is installed for the first time.

However the use of rule based styles where the styles are stored in some 
different system that invokes them according to whatever is specified 
for a particular layer seems to be a different and more complicated 
process. In the majority of cases when the rules were set up for each 
layer, the styles for them were selected directly from the ones already 
defined in the styles manager, and seemed to work satisfactorily in that 
the SVG symbols appeared as expected.

However it seems that every time the software is installed for the first 
time on a newly installed computer, the rule based styling is unable to 
locate the SVG symbols that are needed for these styles even although 
the style manager for the software has no difficulty in finding and 
displaying them.

There is a GUI option in the System tab for setting paths for searching 
for SVG symbols. So far I have not experienced that specifying paths in 
this area causes the missing SVG symbols to reappear when a project is 
opened.

I think it would be of considerable assistance at this point to have an 
understanding of how the SVG symbols are looked up and stored in 
rule-based styles. Although there is a lack of clarity about where the 
styles information in the Styles Manager is read in from when the 
software starts up, this part of the software appears to have little 
difficulty in looking up SVG symbols and displaying them, compared to 
what is happening with per-layer rule-based styling.