22
Copyright © 2012 Op en G eos pati al Consortium
_min_visibility_limitpx[max_visibility_limitpx] The IGG W3DS set up for 3DPIE serves
only a single layer called “citygml:Building” in four different styles named “footprint”, “extruded”, “geometry” and “collada”.
Responded 3D scenes are tiled, but not in a conventional way. The returned master KML file containing pointers to the relevant cached building files is itself untiled. Each
building that the master file points to is contained in a region of its own see Region tag in the KML specification. The region with all features it contains, in this case just the
building, becomes visible when it reaches min_visibility_limit pixel size specified in the request, it becomes invisible again after reaching max_visibility_limit. If no
visibility limits are specified and only one style is defined in the request , the regions that is, the buildings are always visible min_visibility_limit = 0, ma x_visibility_limit =
-1. If no visibility limits are specified and more than one style is defined in the request , predefined visibility limits apply 0px20px for footprint, 20px40px for e xtrude d,
40px60p x for geometry, 60px-1px for COLLADA.
Examples of GetScene requests are: http:IGG.3DPIE.OGC.orgW3DSBerlin?SERVICE=W3DSREQUEST=GetSceneV
ERSION=0.4.0CRS=EPSG:4326FORMAT=modelkmlBoundingBox=13.40154,52 .533,13.406,52.53615LAYERS=citygml:BuildingSTYLES=collada
http:IGG.3DPIE.OGC.orgW3DSBerlin?SERVICE=W3DSREQUEST=GetSceneV ERSION=0.4.0CRS=EPSG:4326FORMAT=modelkmlBoundingBox=13.40154,52
.533,13.406,52.53615LAYERS=citygml:Building,citygml:BuildingSTYLES=geomet ry_10px45p x,collada_45px
Through the course of 3DPIE it turned out that an export of X3D directly from a 3DCityDB could be a valuable building block of a standards -based 3D portrayal pipeline.
This could be used, e.g., to load specific data sets, e.g., buildings in a planning area, into X3D-enabled clients. This might be useful, e.g., for cases, where a full W3DS which of
course could also deliver X3D is not required. Also, such capabilities could help to implement and set up a W3DS that does provide data in X3D format such as shown for
the case of IGG’s W3DS in this experiment.
8.1.2 Paris data import and W 3DS configuration
The Paris data provided by IGN in a series of CityGML files covered an area of approximately 137 km2 of the Paris city center. It was provided in a tiled form: The
whole bounding box 643174.3, 6857518.932, 657513.248, 6867080.967 was divided into 434 tiles that summed up to 50 GB.
This complete dataset was imported into a 3DCityDB hosted at IGG by means of the 3DCityDB ImporterExporter Tool. This tool is provided along with the 3DCityDB and
allows a user to easily load CityGML data into the database.
Then, from the filled 3DCityDB a relevant subset of this data was exported directly into the KMLCOLLADA format using again the ImporterExporter Tool. It achieves data
Copyright © 2012 Op en Geos pati al Consortium
23 export from 3DCityDB and format conversion into KMLCOLLADA in one single
step. The ImporterExporter Tool allows a user to precisely control the export and conversion process. This includes, e.g., the region and object types to export, the level of
detail to use, color parameters and texture settings, KML-specifics to apply, and usage of the Google elevation service to position objects correctly
on Google’s terrain model. Also, settings were chosen so that for each building a subfolder named after the
building’s gml:id was generated. Each subfolder would contain four different files for the same building, one for each style. The file name results from the combination of the
building’s gml:id and the style’s name. As a result of this naming strategy each Building is accessible under the URI
http:W3DS_addressfolder_for_building_layerbuilding_gmlidbuilding_gmli d_style.kmz. These KMLCOLLADA files
serve as the service’s cache; they are generated only once. Later, these URIs will be dynamically embedded in the master file
that are created and returned as service response by the W3DS. The transparent structure of the links makes debugging and possible future enhancements of the W3DS a
straightforward task.
After this generation of KMLCOLLADA files per building, the whole subfolder collection for buildings was copied to the WebContent folder of the IGG W3DS. The
WebContent folder is, as the name implies, the default root folder all cached contents for a servlet are delivered from. The business logic layer of the IGG W3DS is written
accordingly to pick the right files from the right subfolder in WebContent when the corresponding gml:id of a building was found inside the Bounding Box of the W3DS
GetScene request. The business logic is the same for all IGG Web 3D Service instances. Only the
service’s connection data must be adapted to connect to the right database and be able to check a
request’s bounding box against the correct 3D city model data.
8.2 Importing Be rlin data into IGG We b 3D Se rvice
