I know that there are already many questions regarding this matter. In fact, I have already seen the following questions:

I am working on making a plugin for QGIS 2.18 using python 2.7 on Windows. Here is my code:


wms_url = wms_url + "&styles="
# setting prefix path of qgis
# TODO: get this path dynamically
qgis_prefix = "C:\\OSGeo4W64\\apps\\qgis-ltr"
QgsApplication.setPrefixPath(qgis_prefix, True)

#adding the WMS Layer
rlayer = QgsRasterLayer(wms_url, 'default map', 'wms, True)

Once this code is executed, the following messages are seen:



Raster layer: Provider is not valid (provider: wms, URI: http://localhost/MapServer/mapserv.exe?map=Mapfile.map&request=GetMap&service=WMS&version=1.3.0&layers=Layer&width=480.000&height=480.000&format=image/png&bbox=8.473957,77.262417,8.519412,77.307871&crs=EPSG:4326&styles=

(The second line contains a u' and followed by a p and b tad at the start of the statement in the console; I am unable to show it exactly here)

Logs: QGIS Log Error

(It says Download of capabilities failed: Protocol "" is unknown)

Based on the answers I read, I have also tried the following:

  1. Changing the url to http://localhost/MapServer/mapserv.exe?map=Mapfile.map&layers=Layer&styles=&format=image/png&crs=EPSG:4326
  2. Clearing the QGIS cache
  3. Adding the prefix path to QgsApplication (evident from the code).

I should also add that this url works perfectly when run on web browser or if the url http://localhost/MapServer/mapserv.exe?map=Mapfile.map is added to "Add WMS/WMTS Layer" (GUI option). Also, if I remove the 'wms' in the above code, then an image is added, although it does not get loaded to the correct dimensions.

Is there something else that I am missing?

Some Additional Info

From the following link pyQGIS Developer Cookbook

Alternatively you can load a raster layer from WMS server. However currently it’s not possible to access GetCapabilities response from API — you have to know what layers you want:

urlWithParams = 'url=http://irs.gis-lab.info/? 
rlayer = QgsRasterLayer(urlWithParams, 'some layer name', 'wms')
if not rlayer.isValid():
  print "Layer failed to load!"

This suggests that the first parameter should be the full URL to the WMS request with the provider being 'wms' as visible in the code above.

  • Note from the WMS specification the & is used at the end of the parameter and the equals sign can be omitted, so a default style would be styles& not &styles=
    – nmtoken
    Commented Jul 10, 2018 at 10:44
  • 1
    Width and height should be integers not decimals, this might also cause you problems so width=480&height=480& not width=480.000&height=480.000&`
    – nmtoken
    Commented Jul 10, 2018 at 10:57

1 Answer 1


I do not really know the reason, but changing the entered URL to the following format works:

wms_url = "url=http://localhost/MapServer/mapserv.exe?map=Mapfile.map&layers=layers&styles=&format=image/png&crs=EPSG:4326

It was basically to add a url= before the entered URL and keeping the entered request to contain only the map, layers, styles, format and crs parameters. Also, it seems to work even without the QgsApplication part of the code for me.

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