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Figure 21 : Da ta Ex change between LSIS client and server.
In a last experiment, we proposed to stream replace the CityGML stream with one using JSON as exchange format. JSON is understood in our client based on the three.js library
and begin to appear in geo services. It permits to choose the information that we want to send. First experiments have been done on the geometry part; currently, thematic data
and texture data is not taken into account.
In conclusion, in these experiments, we were interested in the study of 3D urban data transfers between a client and a server. Initially, we studied the possibility of transferring
a CityGML data stream. The size and complexity of data makes it difficult to use such data stream on the client side, especially in the case of clients with limited computation
capacities such as web browsers with WebGL support. In a second step we propose to simplify CityGML data on the server side. We finally made first experiments on a stream
based on JSON. Such kind of data is easily usable with WebGL. It is then possible to send geometric and semantic data to a client.
In the future, LSIS would like to continue their work to offer a most successful prototype using WebGL. It would use a JSON data stream. Even if they can have a tiling and LOD
process for urban data, it would be interesting to hide some parts behind 2D data by using a process similar to billboarding based, e.g., on images retrieved from a WVS.
8.14 Re nde ring W 3DS data in the we b browse r
Test data setup: Mainz data set Server: CityServer3D
Using a CitySe rve r3D we b-inte rface to rende r W 3DS-delive re d data in the client browse r
The X3DOM 3D City Viewer, as the name implies, is based on X3DOM, a technology also developed at Fraunhofer IGD. It is based on Javascript and WebGL or Stage3D,
which together cover a major and rising share of installed browsers.
Short Description of X3DO M 3D City Vie we r
The screen in Figure 22 is divided in a 3D display to the left and an OpenStreetMap display to the right. In the map display you can move or zoom with the buttons next to
Viewer
GET Request CityGML
Listener on .w3go
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the upper left corner of the map. You can click with the left mouse button in the map and drag the mouse. This opens up a rectangular area which is to be displayed in the 3D view.
Within the 3D view you can click and drag with the mouse to rotate the 3D view. You can also click right and drag to zoom.
Figure 22 : X3 DO M City Viewer.
8.15 Re nde ring W 3DS data on mobile de vices
Test data: Mainz data set Server: CityServer3D
X3DO M city vie we r ove r Firefox on Android 2.3
The x3dom city viewer web interface shown above can be used on mobile devices. Currently, the x3dom component cannot actually be used, because touch -based
interaction as is common on mobile devices is not yet implemented in X3DOM. However the component renders the geometries delivered over W3DS without noticeable
additional delay compared to a desktop system. Figure 23 and Figure 24 show the X3DOM city viewer running on a smartphone and a tablet, both running Android 2.3
oeprating system.
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Figure 23 : X3 DO M City Viewer on Android 2.3 Samsung Galax y S II.
Figure 24 : X3 DO M City Viewer on BN NOO K colo r with Firefox and Android 2.3.
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8.16 Exte nde d LO D conce pt for X3D
