Get the QGIS-native QML style for a layer

Returns the path to a layer's QML — the QGIS-native form of its symbology, complete in a way the registry is not. gq_reg_main() and the gq_tmap_style() / gq_mapgl_style() translators model roughly 20 symbol properties and a single symbol layer, because that is what tmap and mapgl can render. A QML carries everything QGIS authored: multi-layer symbols, casing and overlay, labelling, per-class dash. Use the registry for tmap and mapgl, and this for anything that speaks to QGIS — Desktop, Mergin field projects, QGIS Server / QWC2, or a layer_styles table.

Usage

gq_style_qml(layer_key, template = NULL)

Arguments

layer_key: Layer key, as used by gq_groups() and the registry (e.g. "lake"). See gq_groups() for the roster.
template: Optional project template (e.g. "bcfishpass_mobile"). When supplied, a template-specific override wins over the shared style. Must name a template gq_templates() knows. When NULL (default) the shared style is returned.

Value

A length-one character path to a .qml file.

Details

Unlike every other gq export, this returns a file path rather than a list or a data frame. The QML is shipped as-is, byte-for-byte what QGIS wrote, so handing back a path lets the caller copy it, read it, or write it into a layer_styles row without gq re-serializing it and introducing drift.

Styles are shared across project templates unless a template genuinely diverges — measured upstream, 3 layers of 53 do. Passing template returns that template's override when one exists and the shared style otherwise, so naming a valid template is always safe. An unknown template name errors rather than falling back, since a silent fallback would hand back the shared style on exactly the layers where an override exists because the shared one is wrong for that template.

Examples

# the QGIS-native style for lakes
qml <- gq_style_qml("lake")
basename(qml)
#> [1] "lake.qml"

# a QML is a full QGIS style document, not a property digest
doc <- xml2::read_xml(qml)
xml2::xml_name(xml2::xml_root(doc))
#> [1] "qgis"

# three layers differ between templates; the rest are shared
basename(dirname(gq_style_qml("land_ownership", "bcfishpass_mobile")))
#> [1] "bcfishpass_mobile"
basename(dirname(gq_style_qml("land_ownership", "bcrestoration_mobile")))
#> [1] "vector"