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  The Open GIS Consortium, Inc. (OGC) is a not-for-profit membership organization founded in 1994 to address the lack of interoperability among systems that process georeferenced data, and between these systems and mainstream computing systems. The OGC has produced a specification for sharing map data over the Web using a service called a Web Map Server (WMS). SRI International has produced an OGC-compliant WMS interface to their TerraVision datasets, thus furthering our commitment to open standards.

Formats

The SRI Web Map Server supports versions 1.0.0 and 1.1.0 of the WMS specification and can return imagery and elevation products in GeoVRML format as well as GIF, JPEG, PPM, and raw grids.



The figures above show a map request for the entire earth, where the requested formats are a JPEG image and a GeoVRML model. The URL for the first of these is shown below. To return the GeoVRML model, you can simply change the format parameter to "geovrml". [ Click for Image | Click for GeoVRML ]

http://www.tvgeo.com/wms?request=map&wmtver=1.0&
format=jpeg&layers=gtopo30.oi&styles=&
srs=EPSG:4326&bbox=-180,-90,180,90&
width=240&height=120


These next two figures show a map request for an elevation model of the Yosemite Valley in California. The requested formats in this case are GIF and GeoVRML. The WMS 1.1 map request URL for the first of these is given below. [ Click for Image | Click for GeoVRML ]

http://www.tvgeo.com/wms?request=GetMap&version=1.1&
format=gif&layers=yosemite.dem&styles=&exceptions=&
srs=EPSG:32611&bbox=258126,4167780,279000,4190000&
width=150&height=150


These two GeoVRML models show the data fusion capabilities of the SRI Web Map Server. When creating a GeoVRML model, you can specify both an elevation and an imagery layer. The elevation layer will then be used to create the underlying geometry and the imagery will be draped over the top. [ Click for DEM | Click for DEM+Image ]

http://www.tvgeo.com/wms?request=map&wmtver=1.0&
format=geovrml&layers=laguna_beach.dem,laguna_beach.oi&
styles=&srs=EPSG:32611&width=128&height=128&
bbox=420000,3710000,430000,3720000

Layers

The SRI Web Map Server supports version 1.0.0 and 1.1.0 of the WMS Capabilities XML. This is used to describe the list of layers available from the server, their extents, and other details. The SRI WMS allows access to most of the TerraVision datasets, including imagery and elevation datasets. The exact set of layers can be discovered by performing a query such as one of the following:

http://www.tvgeo.com/wms?request=GetCapabilities&version=1.1
[ Click for WMS 1.1 Capabilities XML ]

http://www.tvgeo.com/wms?request=capabilities&wmtver=1.0
[ Click for WMS 1.0 Capabilities XML ]

TerraVision Support

The tsmApi library, and hence the TerraVision system, has been augmented to query an OGC-compliant Web Map Server to discover the set of layers available, and then to stream the available imagery over the Web. Therefore, in TerraVision, you can simply add a WMS server URL to your dataset database and it will be treated just like a TerraVision server. N.B. A WMS server is identified by the use of a question mark symbol in the URL, e.g. "http://www.tvgeo.com/wms?".

TerraVision needs to know the resolution of a layer in order to render it. Under WMS 1.1, this can be specified in the resx and resy attributes of the BoundingBox tag. Otherwise, if a ScaleHint tag is provided, we use the min attribute as the dataset's resolution (in meters). TerraVision requests tiles from a WMS in RAW or JPEG format.

Below is a screenshot of TerraVision flying around a large LANDSAT satellite mosaic being server from the NASA Jet Propulsion Lab (JPL) Web Map Server at wmt.jpl.nasa.gov. This shows TerraVision interoperating seamlessly with other WMS implementations.

Resources

 

 

Copyright © 2002 SRI International. All rights reserved.

For more information, please contact: digital-earth@ai.sri.com.
Last updated: Friday, 29-Jun-2001 18:55:07 PDT.