[Qgis-user] Questions regarding WMS layers

[Richard Duivenvoorde]

On 4/13/22 17:07, nagyrobi_r--- via Qgis-user wrote:

I'd say: start using it, and do not use the parts you have questions about :-)
Those are mostly used for 'special' cases (I'll try to explain below).

> 1. I have seen these settings in ADD new WMS connection. Could anybody explain to me what are the settings marked with yellow? What do they do? When to use them? HTTP headers?  Advanced? Ignore GetMap URI reported in the get capabilities? Ignore Getfeatureinfo URI reported in the get capabilities?

HTTP Headers: some services need a special 'referer'-Header, else they will not work (these are there to make it more difficult for others to use the service....). But by setting this (http) Header we can sometimes fool the service a little.

The Advanced section is actually the same: some (not so standard) services want special HTTP-headers to work. Http Headers are always key-value pairs, so in this way you can add some custom header key/value pairs, which QGIS then will sent with every request. Normally these are not needed.

Ignore Get*
The 'GetCapabilities'-request is the request you sent before requesting a map, just to know what the available (in the service) layers/styles/crs's etc etc are).
In early days, a lot of WMS services were not very well configured.
So in the xml then the 'url's' for all kind of services were set to 'http://localhost/....', which makes it for QGIS impossible to retrieve the /tile/map/legendgraphic/featureinfo. But we knew most of the time, that we actually needed to use the same hostname/url as used for the GetCapabilities-url... So in this way you could handle bad configured WMS's.

As said: nowadays you can (unless you have issues) just ignore these 'work arounds'...

> 2. When adding a new WMS layer. Could anybody explain what does the Step Size mean? when to use it? What is "contextual WMS legend" when to use it?

For these I'm not clear, but I think these are related to tiled-WMS (in which you are not trying to get one image, but you request them in parts like 256x256 pixels).
I'm not sure what 'stepsize' is... others?

A contextual legend is (I think) a legend which changes based on the zoom level or area you are in.
I think it makes QGIS request fresh legend (images) for every change of zoom/pan... but others please correct me if wrong.

Again: leave all those blank and try if that works for you :-)

Regards,

Richard Duivenvoorde