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Information on NOAA Ocean Service's nowCOAST's LayerInfo Web Service

Short Description:

nowCOAST's LayerInfo web service provides access to additional useful layer information not available through the use of nowCOAST map services, including Legends, Timestamps, Icons, and Layer Descriptions.

Background:

In addition to the web viewer located at http://nowcoast.noaa.gov, nowCOAST presently provides public access to its observations, forecasts, imagery and geo-referenced hyperlink layers via two different types of Map Services: Through its ArcIMS Image Service as well as through an Open Geospatial Consortium (OGC)-compliant Web Map Service (see our Map Services page for more information). Unfortunately, due to limitations of the ArcIMS platform, it is difficult and in some cases impossible to obtain additional information about each layer, such as the data's Valid Timestamp, Legend Graphics, or Layer Descriptions. To solve this problem, the nowCOAST team has implemented a "LayerInfo" HTTP-based web service that allows users to retrieve useful information about each layer.

Information Provided by the LayerInfo Web Service:

Currently, nowCOAST's LayerInfo web service provides access to four types of layer information:
  • Legend Graphics
        Many of nowCOAST's on-map data layers are displayed using complex symbology, which often requires the user to interpret a symbol or color to determine discrete values. For example, requesting a legend for the Weather Radar Mosaic layer returns a graphic that associates on-map color values to actual dbZ values, and requesting a legend for the Surface Wind Speed/Direction Observations layer returns a graphic instructing the user how to infer a numerical Knot or Miles per hour value from a Wind Barb symbol.

             Example of Weather Radar Mosaic Legend Graphic returned by LayerInfo service:



  • Valid Timestamps
        The various on-map data layers shown on nowCOAST represent environmental conditions at specific points in time. Throughout the day, nowCOAST is constantly updating its on-map observation, imagery, analysis and forecast layers as new data is made available, and for many of nowCOAST's customers, knowing at what time each layer is valid is just as important as the data itself. Previously, Map Service users had no way of programmatically determining these valid times for nowCOAST's layers. But now, through the use of nowCOAST's LayerInfo service, the valid times for all of nowCOAST's on-map layers are easily accessible.

             Example of Weather Radar Mosaic Valid Timestamp returned by LayerInfo service:

    Thu Jun 10 4:12 PM EDT


  • Layer Descriptions
        Often times users require additional information about a layer, including background information on the layer's data source(s), visualization technique, or update frequency. This information is now available both on the nowCOAST map viewer (by clicking on a layer's name in the Table of Contents) and through the nowCOAST LayerInfo web service. Layer descriptions are returned in HTML format, often times with embedded screenshots.

  • Layer Icons
        Sometimes it is difficult for a user to know what data is being represented just by reading a layer's title. In these cases, it can be beneficial to display next to the title a small icon (approximately 20x19 pixels) that represents a graphical depiction of the layer. By taking a quick glance at a layer's icon, it is easy to remember what type of data is represented, which saves the user time. The nowCOAST LayerInfo web service now provides access to these images through a simple web request.

             Example:

    Weather Radar Mosaic Layer Icon image returned by LayerInfo service


Requesting Information from the LayerInfo Web Service:

The nowCOAST LayerInfo web service is located at the following base URL:

        http://nowcoast.noaa.gov/LayerInfo?

In order to retrieve data from this service, the user must include valid values for the parameters "layer" and "data". The "layer" parameter references the target layer's identifier, while "data" represents the desired type of data to be returned.

The formal syntax of a request can be defined as follows (in BNF-style notation):

    http://nowcoast.noaa.gov/LayerInfo?layer=<layer identifier>&data={legend | icon | description | timestamp[&output={xml | html | plaintext}]}

In plain language, this means that a user must specify the target layer's identifier for the "layer" parameter, as well as one of the following values for the "data" parameter: "legend", "icon", "description", or "timestamp". In addition, the format of a timestamp response can be specified as HTML (default), XML, or Plain Text by appending "&output=html", "&output=xml", or "&output=plaintext", respectively, to the request URL.

A list of valid Layer Identifiers to specify in a request can be found in either the WMS Capabilities.xml file (retrieved through a WMS GetCapabilities request) or on the nowCOAST "Bookmarkable Views" page at: http://nowcoast.noaa.gov/help/regional_links.shtml

It is also worth noting that any requests for legend images or layer icons can be embedded as images directly in your own HTML page. Simply enclose the target legend URL in an HTML <img> tag.

Example of Embedding a Legend Graphic in HTML:
     <img src="http://nowcoast.noaa.gov/LayerInfo?layer=RAS_RIDGE_NEXRAD&data=legend" />

Example LayerInfo Requests:


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