[MapProxy] add a wmts layer

[Martijn Coenen]

Raffaello,

> ok sorry, it was only my personal point of view, i've just posted before. no response.
> here again:
> The error (maybe is a warning, cause the icon is yellow) got from Chrome using openlayers connect wmts mapproxy:
> 
> Resource interpreted as Image but transferred with MIME type application/vnd.ogc.se_xml: "http://192.168.198.138/wsgi-mapproxy/service/grids_demo_osm/EPSG:4326:1/0/0.png". 

I have had this same problem with an unrelated (to Mapproxy) project. It happens when there is no tile for the given point. An XML error message is send back from the source instead of the requested PNG image.

Is the WMTS source publicly available? If so, we can see what's going on there. 

Regards,
Martijn