is it possible to load the geometry of LoD2 files in CityGML format (gml:LinearRing from bldg:GroundSurface) as GML layer in QGIS?
Here is an example content of a citygml file:
<?xml version="1.0" encoding="windows-1252" standalone="yes"?>
<core:CityModel xmlns:xal="urn:oasis:names:tc:ciq:xsdschema:xAL:2.0"
xmlns:gml="http://www.opengis.net/gml" xmlns:app="http://www.opengis.net/citygml/appearance/1.0"
xmlns:core="http://www.opengis.net/citygml/1.0"
xmlns:tex="http://www.opengis.net/citygml/texturedsurface/1.0"
xmlns:dem="http://www.opengis.net/citygml/relief/1.0"
xmlns:veg="http://www.opengis.net/citygml/vegetation/1.0"
xmlns:wtr="http://www.opengis.net/citygml/waterbody/1.0"
xmlns:tran="http://www.opengis.net/citygml/transportation/1.0"
xmlns:bldg="http://www.opengis.net/citygml/building/1.0"
xmlns:frn="http://www.opengis.net/citygml/cityfurniture/1.0"
xmlns:grp="http://www.opengis.net/citygml/cityobjectgroup/1.0"
xmlns:gen="http://www.opengis.net/citygml/generics/1.0" xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:luse="http://www.opengis.net/citygml/landuse/1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.opengis.net/citygml/building/1.0 http://schemas.opengis.net/citygml/building/1.0/building.xsd http://www.opengis.net/citygml/cityfurniture/1.0 http://schemas.opengis.net/citygml/cityfurniture/1.0/cityFurniture.xsd http://www.opengis.net/citygml/appearance/1.0 http://schemas.opengis.net/citygml/appearance/1.0/appearance.xsd http://www.opengis.net/citygml/cityobjectgroup/1.0 http://schemas.opengis.net/citygml/cityobjectgroup/1.0/cityObjectGroup.xsd http://www.opengis.net/citygml/generics/1.0 http://schemas.opengis.net/citygml/generics/1.0/generics.xsd http://www.opengis.net/citygml/texturedsurface/1.0 http://schemas.opengis.net/citygml/texturedsurface/1.0/texturedSurface.xsd http://www.opengis.net/citygml/relief/1.0 http://schemas.opengis.net/citygml/relief/1.0/relief.xsd http://www.opengis.net/citygml/vegetation/1.0 http://schemas.opengis.net/citygml/vegetation/1.0/vegetation.xsd http://www.opengis.net/citygml/waterbody/1.0 http://schemas.opengis.net/citygml/waterbody/1.0/waterBody.xsd http://www.opengis.net/citygml/transportation/1.0 http://schemas.opengis.net/citygml/transportation/1.0/transportation.xsd http://www.opengis.net/citygml/landuse/1.0 http://schemas.opengis.net/citygml/landuse/1.0/landUse.xsd">
<gml:name>LoD2_640_5630</gml:name>
<gml:boundedBy>
<gml:Envelope srsName="urn:adv:crs:ETRS89_UTM32*DE_DHHN92_NH">
<gml:lowerCorner srsDimension="3">640000.0 5630000.0 307.898</gml:lowerCorner>
<gml:upperCorner srsDimension="3">642000.0 5632000.0 377.3</gml:upperCorner>
</gml:Envelope>
</gml:boundedBy>
<core:cityObjectMember>
<bldg:Building gml:id="DEXXLLLP00006Pxo">
<core:creationDate>2017-05-06</core:creationDate>
<core:externalReference>
<core:informationSystem>http://repository.gdi-de.org/schemas/adv/citygml/fdv/art.htm#_9100</core:informationSystem>
<core:externalObject>
<core:name>DEXXLLLP00006Pxo</core:name>
</core:externalObject>
</core:externalReference>
<gen:stringAttribute name="DatenquelleDachhoehe">
<gen:value>3000</gen:value>
</gen:stringAttribute>
<gen:stringAttribute name="DatenquelleLage">
<gen:value>1000</gen:value>
</gen:stringAttribute>
<gen:stringAttribute name="Gemeindeschluessel">
<gen:value>21070099</gen:value>
</gen:stringAttribute>
<gen:stringAttribute name="DatenquelleBodenhoehe">
<gen:value>1200</gen:value>
</gen:stringAttribute>
<bldg:function>31001_1000</bldg:function>
<bldg:roofType>1000</bldg:roofType>
<bldg:measuredHeight uom="urn:adv:uom:m">3.0</bldg:measuredHeight>
<bldg:lod2Solid>
<gml:Solid>
<gml:exterior>
<gml:CompositeSurface>
<gml:surfaceMember xlink:href="#GUID_18276819466395891000_34_2_5"/>
<gml:surfaceMember xlink:href="#GUID_18276819466395891000_34_2_4"/>
<gml:surfaceMember xlink:href="#GUID_18276819466395891000_34_2_3"/>
<gml:surfaceMember xlink:href="#GUID_18276819466395891000_34_2_2"/>
<gml:surfaceMember xlink:href="#GUID_18276819466395891000_34_2_1"/>
<gml:surfaceMember xlink:href="#GUID_18276819466395891000_34_2_0"/>
</gml:CompositeSurface>
</gml:exterior>
</gml:Solid>
</bldg:lod2Solid>
<bldg:boundedBy>
<bldg:WallSurface gml:id="UUID_1dbc290a-720c-4859-98f5-b55d5a21768b">
<core:creationDate>2017-05-06</core:creationDate>
<bldg:lod2MultiSurface>
<gml:MultiSurface gml:id="UUID_434bd186-0c4d-4245-9b66-d0de541b402d">
<gml:surfaceMember>
<gml:Polygon gml:id="GUID_18276819466395891000_34_2_1">
<gml:exterior>
<gml:LinearRing gml:id="GUID_18276819466395891000_34_2_1_0_">
<gml:posList srsDimension="3">641970.53 5631759.65 314.514 641969.331
5631756.724 314.514 641969.331 5631756.724 311.514 641970.53 5631759.65
311.514 641970.53 5631759.65 314.514</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</gml:surfaceMember>
</gml:MultiSurface>
</bldg:lod2MultiSurface>
</bldg:WallSurface>
</bldg:boundedBy>
<bldg:boundedBy>
<bldg:WallSurface gml:id="UUID_b1c68a9c-e621-4d2f-8c26-c5f14ae8f666">
<core:creationDate>2017-05-06</core:creationDate>
<bldg:lod2MultiSurface>
<gml:MultiSurface gml:id="UUID_2bac2d98-c7f6-4b6a-9a23-4fdcc8bd8fa0">
<gml:surfaceMember>
<gml:Polygon gml:id="GUID_18276819466395891000_34_2_2">
<gml:exterior>
<gml:LinearRing gml:id="GUID_18276819466395891000_34_2_2_0_">
<gml:posList srsDimension="3">641969.331 5631756.724 314.514 641967.925
5631757.149 314.514 641967.925 5631757.149 311.514 641969.331 5631756.724
311.514 641969.331 5631756.724 314.514</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</gml:surfaceMember>
</gml:MultiSurface>
</bldg:lod2MultiSurface>
</bldg:WallSurface>
</bldg:boundedBy>
<bldg:boundedBy>
<bldg:WallSurface gml:id="UUID_344769a9-ed9c-409e-99f1-6c969137a92d">
<core:creationDate>2017-05-06</core:creationDate>
<bldg:lod2MultiSurface>
<gml:MultiSurface gml:id="UUID_a403b938-462b-4c48-bbda-ef45a47f094a">
<gml:surfaceMember>
<gml:Polygon gml:id="GUID_18276819466395891000_34_2_3">
<gml:exterior>
<gml:LinearRing gml:id="GUID_18276819466395891000_34_2_3_0_">
<gml:posList srsDimension="3">641967.925 5631757.149 314.514 641968.414
5631760.471 314.514 641968.414 5631760.471 311.514 641967.925 5631757.149
311.514 641967.925 5631757.149 314.514</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</gml:surfaceMember>
</gml:MultiSurface>
</bldg:lod2MultiSurface>
</bldg:WallSurface>
</bldg:boundedBy>
<bldg:boundedBy>
<bldg:WallSurface gml:id="UUID_7f233674-d55b-45e8-a079-5034984054fc">
<core:creationDate>2017-05-06</core:creationDate>
<bldg:lod2MultiSurface>
<gml:MultiSurface gml:id="UUID_cbbd8499-5ed8-468c-8bf1-a38de5369dc7">
<gml:surfaceMember>
<gml:Polygon gml:id="GUID_18276819466395891000_34_2_4">
<gml:exterior>
<gml:LinearRing gml:id="GUID_18276819466395891000_34_2_4_0_">
<gml:posList srsDimension="3">641968.414 5631760.471 314.514 641970.53
5631759.65 314.514 641970.53 5631759.65 311.514 641968.414 5631760.471
311.514 641968.414 5631760.471 314.514</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</gml:surfaceMember>
</gml:MultiSurface>
</bldg:lod2MultiSurface>
</bldg:WallSurface>
</bldg:boundedBy>
<bldg:boundedBy>
<bldg:RoofSurface gml:id="UUID_b3e3f0b8-91aa-45ca-9a7c-5433796d82ef">
<core:creationDate>2017-05-06</core:creationDate>
<bldg:lod2MultiSurface>
<gml:MultiSurface gml:id="UUID_67410ae6-edaa-4748-b531-a0b12ddd6efc">
<gml:surfaceMember>
<gml:Polygon gml:id="GUID_18276819466395891000_34_2_5">
<gml:exterior>
<gml:LinearRing gml:id="GUID_18276819466395891000_34_2_5_0_">
<gml:posList srsDimension="3">641968.414 5631760.471 314.514 641967.925
5631757.149 314.514 641969.331 5631756.724 314.514 641970.53 5631759.65
314.514 641968.414 5631760.471 314.514</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</gml:surfaceMember>
</gml:MultiSurface>
</bldg:lod2MultiSurface>
</bldg:RoofSurface>
</bldg:boundedBy>
<bldg:boundedBy>
<bldg:GroundSurface gml:id="UUID_ad937406-df68-4264-9970-7d1071ef9df4">
<core:creationDate>2017-05-06</core:creationDate>
<bldg:lod2MultiSurface>
<gml:MultiSurface gml:id="UUID_f4aa1c70-31e9-437d-bc47-4892e508d69a">
<gml:surfaceMember>
<gml:Polygon gml:id="GUID_18276819466395891000_34_2_0">
<gml:exterior>
<gml:LinearRing gml:id="GUID_18276819466395891000_34_2_0_0_">
<gml:posList srsDimension="3">641970.53 5631759.65 311.514 641969.331
5631756.724 311.514 641967.925 5631757.149 311.514 641968.414 5631760.471
311.514 641970.53 5631759.65 311.514</gml:posList>
</gml:LinearRing>
</gml:exterior>
</gml:Polygon>
</gml:surfaceMember>
</gml:MultiSurface>
</bldg:lod2MultiSurface>
</bldg:GroundSurface>
</bldg:boundedBy>
</bldg:Building>
</core:cityObjectMember>
</core:CityModel>