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CityGML

The CityGML format (City Geography Markup Language) is a data interchange format for 3D-data for geometries of cities and areas. The format is based on GML3 (see http://www.citygml.org).

Note that a CityGML file represents one of several possible refinement levels (Level-of-Detail, LoD):

Level-of-Detail (LoD) Original Description Remarks
LoD 0 regional, landscape (not useful, missing building heights)
LoD 1 city, region useful data format for noise calculations (includes building heights, but no roof structures, i.e. „box-type model“)
LoD 2 city districts, projects buildings with standardized roof structures, additional terrain features are imported as terrain contours
LoD 3 architectural models (outside), landmarks buildings with refined structures, importable by activating option „Import LoD 3“ (see below for further specifications)
LoD 4 architectural models (interior) (not usable, interior model)

By default, CadnaA imports all objects from LoD 0 to LoD 2. Optionally, also import of LoD 3 is possible, although the results vary since LoD 3 is in general too detailed with respect to the type of objects used in CadnaA. In LoD 3, for example, a building might be split into 10 or more separate building objects in CadnaA.

Import Options (CityGML)

Dialog Options for Import (for CityGML)

Layer Types

The CityGML format uses fixed descriptions for object layers (regarding allocation of layers see Allocate Object Type to Layer). These layer descriptions are predefined on the Options for Import dialog.

This concerns the following CadnaA object types:

Object Type Layer Description
road Road
railway Railway
building Building(Part|)|RoofSurface
barrier CN*|NC*
foliage PlantCover
contour line lod2TerrainIntersection|ReliefFeature|UL*
area of designated use LandUse
auxiliary polygon * (remaining objects)

Further Options

The following CityGML-specific options are available:

  • Import only Section (see Import only Section)
  • Simplify Geo automatically (see Simplify Geometry in the manual „Introduction to CadnaA“)
  • Unknown Attributes to Memo-Variables (default: ON): see Unknown Attributes to Memo-Variable
  • option „Reconstruct DTM from buildings' ground floors“: When activated, the import of
    • LoD1 data creates a contour line for each ground surface (horizontal surface with min height) of each building.
    • LoD2 data creates a contour line for all polygons marked as „ground Surface“ contained in the file.
  • option „Import LoD 3“: When activated, also „Level-of-Detail 3“ data will be imported. Since LoD3 data does not necessarily comply with CadnaA‘s internal object structure, it is not sure whether the import result can be used directly for calculations. Check for correctness of the data imported, otherwise further corrections, adjustments and editing may be required.

Building geometry for LoD2

The following options are available when importing LoD2 data:

  • Building parts on their own (not recommended): For each roof surface, a single building object is created. Therefore, "simple" houses with sloped roofs typically result in two building objects. If gables or similar are present, the import may result in significantly more objects. This option has disadvantages in terms of
    • Calculation: Reflections may be considered twice, since facades or "inner walls" may be present twice.
    • Use of building evaluations: Since a house consists of several building objects, several building evaluations would also have to be used here.
  • Convert to LoD1 (average roof height) (recommended): For each building contained in the LoD2 dataset a CadnaA building object with a flat roof is created. The height of the flat roof is defined as an area-weighted average of the heights of the individual sloped roofs.
  • Convert to LoD1 (maximum roof height): as before, but the maximum height among all sloped roofs is used as height.
  • Convert to LoD1 (minimum roof height): as before, but the minimum height among all sloped roofs is used as height.

Coordinate System

Below the text line „Found the following coordinate system“ the designation of the coordinate system found in the CityGML file is displayed. Please note that it is just a hint, since none of the geodetic coordinate systems (see Coordinate System) available in CadnaA is actively selected. Finally, the user has to specify/select the appropriate coordinate system himself (e.g. after having inspected the imported object coordinates).

With no coordinate system being present, the message „not found or no file selected“ is displayed. In this case, the transformation - if any - into a geodetic coordinate system is up to the user.

Buttons

buttons specific to the dialog: