Only create rules/categorized categories/graduated ranges if the
associated symbol could be converted to SLD, and is not an "empty"
symbol.
Otherwise we do not generate a rule, as SLD spec requires a
Symbolizer element to be present.
The old method was very inefficient, as it required a re-load and
re-parse of the associated SVG file content with every clone, only
for many of the parsed properties to be immediately overwritten.
Optimise by just directly copying members, avoiding all unnecessary
work.
This is frequently seen as a hotspot when profiling map renders,
as that involves cloning all symbol layers upfront.
Speeds up a benchtest cloning 100k markers from 4.3 seconds to
150ms.
This new symbol layer type allows placing text labels at regular
intervals along a line (or at positions corresponding to
existing vertices). Positions can be calculated using
Cartesian distances, or interpolated from z/m values.
Functionality includes:
- Labels can be placed using fixed cartesian 2d distances,
at regular linearly interpolated spacing calculated using
the Z or M values in geometries, or at existing vertices
- Labels can show either the running total distance, or
the linearly interpolated Z/M value
- Uses text rendered to draw labels, so the full range
of functionality is available for the labels (including
buffers, shadows, etc)
- Uses the QGIS numeric format classes to format numbers
as strings, so users have full range of customisation
options for eg decimal places
- An optional "skip multiples of" setting. If set, then
labels which are a multiple of this value will be skipped
over. This allows construction of complex referencing labels,
eg where a symbol has two linear referencing symbol layers,
one set to label every 100m in a small font, skipping multiples
of 1000, and a second set to label every 1000m in a big
bold font
- Labels are rendered using an angle calculated by averaging
the linestring, so sharp tiny jaggies don't result in
unslightly label rotation
- Optionally, markers can be placed at referenced points
in the line string, using a full QGIS marker symbol (this allows
eg showing a cross-hatch at the labeled point, for a "ruler"
style line)
- Data defined control over the placement intervals, skip
multiples setting, marker visibility and average angle
calculation length
Notes:
- When using the distance-based placement or labels, the
distances are calculated using 2D only, Cartesian calculations
based on the original layer CRS. This could potentially be
extended in future to expose options for 3D Cartesian distances,
or ellipsoidal distance calculations.
Sponsored by the Swiss QGIS User Group
