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Overview

Scope

The Web View Service (WVS) is a portrayal service for three-dimensional geodata such as landscape models, city models, vegetation models, or transportation infrastructure models. The WVS encapsulates the whole portrayal process at server side and delivers multi-layer rendered images of 3D scenes to the service consumer. The WVS extends the Web Terrain Service (WTS) and the OGC-internal Web Perspective View Service (WPVS); in a way, the WVS can be considered as the 3D counterpart for the well-established Web Map Service (WMS).

Portrayal pipeline.
Portrayal pipeline and separation for full server-side rendering; only images are transferred.

The WVS is designed to overcome the restricted visualization and interaction capabilities of WTS/WPVS-based approaches. As a major extension, the WVS provides additional geometrical and thematic data, such as depth information and object identity information, which are encoded in the retrieved multi-layer images. Additionally, the WVS provides operations for retrieving information on visualized objects at specific image positions, measurement functionalities, and enhanced navigation support. Further extensions target at minimizing communication overhead and minimizing bandwidth usage.
Regardless of a client's 3D rendering hardware and software, the WVS can provide high-quality images of complex 3D geodata since the rendering is performed by a dedicated 3D server system. The image-based approach simplifies the service-based integration of high-quality images of 3D views on 3D geodata into almost any application and system related to 3D geodata, e.g., city web portals, tourist information systems, network planning systems, etc. Due to the server-side data management and rendering, the WVS can be used by resource-limited thin clients and under low bandwidth conditions — the steady transmission of data to clients does not depend on the complexity of the 3D model data. Based on the WVS capabilities, even complex, rich feature 3D clients, supporting, e.g., continuous real-time navigation and interaction in the 3D world, can be built.

Example of a browser-based WVS client. Left: Combination with Google Maps; blue arrow indicates feedback for selecting a new camera position and orientation by selecting locations in the view. Middle: Requesting information for specific objects. Right: Measuring a path in the image. (3D data: Boston Redevelopment Authority)
Example of a browser-based WVS client. Left: Combination with Google Maps; blue arrow indicates feedback for selecting a new camera position and orientation by selecting locations in the view. Middle: Requesting information for specific objects. Right: Measuring a path in the image. (3D data: Boston Redevelopment Authority)

History

In the OGC Military Pilot Project, Phase 1 (MPP-1) three-dimensional portrayal was defined as a new operation GetView on a Web Map Service (WMS). As three-dimensional portrayal adds complexities that are out of scope of a WMS, a new Web Terrain Service (WTS) had been defined and proposed in 2001. OGC-internally, the discussion led to the Web Perspective View Service (WPVS). Generalizing the WPVS approach, the Web View Service (WVS) has been specified. Based on a use case analysis, the main intension of this generalization and extension is to support a consumer of the image-based 3D portrayal service by means for interacting with the image: navigating in the represented scene, retrieving feature information, and analyzing the spatial setting.

Features

Service Interface

Service Operation Description Optionality
GetCapabilities Request a service metadata document that describes the capabilities of the specific server Mandatory
GetView Retrieve a 3D view on a 3D scene Mandatory
GetFeatureInfo Retrieve attribute data of features selected in a 3D view Optional
GetPosition Retrieve the 3D positions at a specified 2D pixel position of a requested view, or a 2D pixel position representing a 3D position in the scene Optional
GetIdentifierMapping Retrieve mappings from object identifiers (object id image) to feature identifiers Optional
GetMeasurement Perform measurements and retrieve the measurement result Optional
GetCamera Retrieve a good camera specification based on the current 3D view Optional

Image Layers

By the GetView operation a GetView service client can retrieve 3D views as images. In addition to color data, the WVS provides thematical and geometrical information as additional image layers. The following figure shows the currently suggested image layers (from left to right): color layer, object id layer, depth layer normal layer, mask layer. These image layers can be requested and processed by a WVS client for supporting user interaction such as 3D navigation or for implementing image processing capabilities.

WVS image layers: COLOR, OBJECTID, DEPTH, NORMAL, MASK (left to right).
WVS image layers: COLOR, OBJECTID, DEPTH, NORMAL, MASK (left to right).

Providing Image Sets

The WVS supports the provision of multiple image layers by one request. These could be a) different image layers for one camera and projection specification or b) multiple image layers for different camera and projection specifications. This allows for a) exploiting server-side rendering optimizations and b) improving bandwith usage by reducing communication overhead.

Multiple Projections

Various application areas could benefit from requesting images that do not show central-perspective projections. Thus, a WVS can provide various projection types. Currently the specification suggests two linear projections: perspective projections and orthographic projections.

Pixel-based Operations

Multiple WVS operations allow a WVS consumer to interact with the image. This includes the retrieval of feature information, the computation of 3D positions, spatial analysis, and smart navigation support.

Extendability

Due to the image-based interface, the WVS-approach for 3D portrayal can be integrated into various applications and systems, e.g., web-portals. For adjusting a WVS server to specific needs and applications, the following aspects of the WVS can be extended: Image layer types and encodings, projection types, analysis methods, navigation methods.

Potentials

For WVS potentials and application examples, have a look at the Potentials section … here.

overview.txt · Last modified: 2010/04/23 17:03 by bhagedorn