Use WMS Services GetMap in MapServer
5.3. Use WMS Services GetMap in MapServer#
GetMap operation is used to generate a map, which can be a
picture or a set of graphic elements.
GetMap allows clients to
request multiple servers to make overlapping map layers, processing
pixel geometry with the same frame of reference, size, and scale. These
layers can be displayed in a certain order on the client side, and
transparent pixel technology can be used to display map information from
different sources according to human visual requirements.
GetMap request usually uses HTTP/GET to call a basic WMS via URL
encoding, and can also use HTTP/POST encoding to communicate with an
SLD-capable WMS. The
GetMap request must specify the requested
layers (Layers), the styles used by each layer (Styles), the spatial
reference system (SRS), the bounding rectangle (BBox), the image format
(Format) and size (Width, Height) and other parameters.
Web map services support the display of map views in picture or graphic format. Image formats include public image formats such as GIF, PNG, JPEG, etc. These formats are supported by most Web browsers, and the display of other graphic formats may also require some helper programs to support. Graphics formats include SVG and WebCGM formats, which are not commonly used in WMS.
In addition, the optional
Transparent parameter is used to specify
whether the background of the map is transparent. The default value is
False . A function that allows the returned result to be drawn
transparently, so that maps for different requests can be overlaid. Each
WMS preferably provides an image format that supports transparent
display for overlaying with other map images.
GetMap request will return a map consisting of georeferenced
layers with the specified style, spatial reference system, bounding
rectangle, size, format, and transparency. An invalid
returns a formatted error message. In the HTTP context, the content type
of the return value is a MIME type.
5.3.1. Request with GetMap#
GetMap access to the published MapServer WMS service is described here.
The first is Mapfile:
Compared to the previous
This Mapfile is configured with the WMS service. View function:
Open a link
5.3.2. View the map#
Here, use the
map mode of MapServer to view.
View the map
5.3.3. Configure with GetMap#
GetMap, you need to enable the
GetMap option in WMS:
If not enabled, the access URL will display :
<ServiceExceptionReport version="1.3.0" xsi:schemaLocation="http://www.opengis.net/ogc http://schemas.opengis.net/wms/1.3.0/exceptions_1_3_0.xsd"><ServiceException> msWMSDispatch(): WMS server error. WMS request not enabled. Check wms/ows_enable_request settings. </ServiceException></ServiceExceptionReport>
Click to view
22.214.171.124. Projection is not set up#
Note that to use
GetMap, the projection must be set. If it is not
set, the access will appear:
<ServiceExceptionReport version="1.3.0" xsi:schemaLocation="http://www.opengis.net/ogc http://schemas.opengis.net/wms/1.3.0/exceptions_1_3_0.xsd"><ServiceException code="InvalidCRS"> msWMSLoadGetMapParams(): WMS server error. Cannot set new CRS on a map that doesn't have any projection set. Please make sure your mapfile has a projection defined at the top level. </ServiceException></ServiceExceptionReport>
Click to view
126.96.36.199. Correct access#
Here is the correct way to access it. Note that the length and width parameters passed to the server graph in URL.
It looks like
GETMAP is similar to MapServer’s
Version of WMS 1.1.1 and WMS 1.3.0 have different request parameter for coordinate system :
5.3.4. Get a partial map with GetMap#
The range used above is consistent with the range of the entire data, and the results look no different. Let’s zoom out to get a section of the map.
Get a partial map with GetMap
According to the description, the parameter
CRS = EPSG: 4326 can
also be used. But I didn’t succeed. You may need to configure mapfile.
The above effect can also be achieved in MapServer CGI control, by
zoom level of browsing, the
of the map but
GetMap is obviously more flexible. In addition to
these, WMS has more advantages as a standard.