SVS Image Server

Asking for an Image

If the user selects the layer with the title "African Fires during 2002 (1024x1024 Animation)", the client constructs a WMS query using the name of the layer, i.e., "2890_17402". This query begins with

In order to complete this request, the query must, at a minimum, include the following additional information about the image being requested:

     +     the format of the image
     +     the width and height of the image in pixels
     +     the geographic region of the earth covered by the image
     +     the style of the image

Without this information in the query, the server will return an error message, or "exception". (Note that the Capabilities XML included


which indicates that the returned exception will be in XML format.)

At the beginning of the Capabilities XML, the image formats supported by the SVS Image Server were defined in the <GetMap> element by


Since PNG (Portable Network Graphics) is a supported format, the query can request a PNG image, i.e.,

The first line in the Capabilities XML for the African Fires layer was

<Layer opaque="0" noSubsets="1" fixedWidth="1024" fixedHeight="1024">

The "fixedWidth" and "fixedHeight" parameters indicate that the images from this layer are only available in one size, 1024x1024 pixels. Using these values, the query now becomes

The "noSubsets" parameter in that line indicates that the only geographic region that can be requested is the full bounding box of the layer, which is given in the line

<BoundingBox CRS="CRS:84" minx="-22" miny="-39" maxx="58" maxy="41"/>

To use this bounding box in the query, separate parameters must be added for both the coordinate reference system (CRS) and the bounding box (BBOX). Now the query takes this form

Finally, a parameter must be added to define the style of the image being returned. The simplest way to request a style is to leave the STYLES parameter blank, which results in a request for the default style for the layer, e.g.,

Accessing this link should return the correct image from the server.

A better solution is to use an available style parameter from the layer description in the Capabilities XML. In this case, the following two lines define the available styles


A request for the first of these styles would look like this:

Note that this image is not the same as the previous one. This one added a background image of Africa, where the first one had a transparent background so it could be laid over any image of Africa. Since the WMS standard does not define which of the available styles is the default, it is better to request a specific style than use the default. A more complete description of styles and their use of this server will be given later in this document.

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Table of Contents

     SVS Image Server Home Page

     Tutorial Introduction
     Accessing the Table of Contents
     Asking for an Image
     Asking for an Animation
     Asking for an Image Sequence
     Design Considerations - Fixed Size Images
     Design Considerations - Projections
     Styles and Legends
     Metadata - Abstracts and Keywords
     Metadata - Attributions and FGDC Metadata


     Available Animations List