[MapProxy] Confused about zoom levels when proxying Google Maps

[Paul William]

Hi all,

I am using MapProxy to proxy Google Maps into an application that supports
WMS servers.

I am new at GIS software and confused by the zoom levels. For some reason,
the MapProxy WMS server only serves up tiles to a maximum of Google's zoom
level 17. If I use MapProxy Seed tool, I can cache tiles at a maximum of 19
(confirmed by look at the images in the cache).

I cannot zoom in as far as the data, regardless of what client I use. The
MapProxy Demo (OpenLayers?) client has the same restriction.

My google.yaml configuration file is very simple.

services:
  demo:
  tms:
  wms:
    md:
      title: MapProxy

sources:
  gh:
    type: tile
    url: http://mt1.google.com/vt/lyrs=y&x=%(x)s&y=%(y)s&z=%(z)s
    grid: gh_grid

grids:
  gh_grid:
    base: GLOBAL_MERCATOR
    origin: ul

caches:
  gh_cache:
    grids: [gh_grid]
    sources: [gh]
    cache:
      type: file
      directory_layout: tms

layers:
  - name: gh_layer
    title: google
    sources: [gh_cache]

Can anyone explain to me why I cannot zoom in to the highest zoom level
when using MapProxy?

Many Thanks. Paul
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