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iShare v6 and later uses MapProxy to create and display cached map data, for example aerial or historic maps. MapProxy may also be useful in other circumstances, for example:

  1. You may have to provide a customer API Key in the URL for each request, as in the case with the OS Maps API. If this were to be used directly in iShare, the key would have to be transferred to the client which could expose it to misuse.

  2. Proxying the basemap through MapProxy allows us to also query it directly with WMS which then means that it should work seamlessly with printing.

Configuration Overview

MapProxy uses a YAML configuration file to define the service - this file will normally be stored with the MapProxy application, for example at D:/mapproxy/mapproxy.yaml. Full documentation on configuring the YAML file are at: https://mapproxy.org/docs/latest/configuration.html, and a sample YAML file is attached to this page.

Configuration of MapProxy layers in Studio is covered in this section: BaseMaps Details .

The YAML file can be edited in a text editor such as Notepad++. The following are the main sections of the YAML file which need to be configured for each layer:

  • Layers: the layers that are available in the service

  • Caches: where the cache is stored

  • Sources: the source of the data to be cached

  • Grid: the Coordinate Reference System used in the layer, and the scales/resolutions available.

Troubleshooting configuration

Bear in mind the following when setting up a MapProxy installation:

  • the syntax and indentation shown in the example file and in the MapProxy documentation should be followed exactly in order to avoid errors

  • any errors will be recorded in the mapproxy.log file, which is normally in the same folder as the mapproxy.yaml file

  • you will need to make sure that any referenced folders are accessible by the MapProxy IIS application pool, and that the MapServer application pool has access to the source data and images

Detailed Configuration

Layers

This section defines one or more layers to be served by MapProxy. Each layer should have:

  • name: used as a reference by Studio in the Details dialog

  • title: descriptive name for display purposes

  • sources: a reference to one or more sources defined elsewhere in the YAML file, defining the data to be displayed

See the example below.

layers:
  - name: aerial2013
    title: Aerial 2013
    sources: [aerial2013_cache]
  - name: aerial2018
    title: Aerial 2018
    sources: [aerial2018_cache]
  - name: basemap
    title: Colour
    sources: [basemap_cache]

Caches

This section defines the location of the cached data. The cache reference in the first line is referenced by the layers section, and the cache also identifies the source of the data.

Each cache will have:

  • grid: a reference to a grid definition elsewhere in the YAML file

  • sources: a reference to one or more source sections - if this is a MapServer WMS, the source include both the reference to the source name in the YAML file (e.g. aerial_wms_2013) and the name of the layer or group in the map file (e.g. aerial2013)

  • cache: details of the cache itself, containing

    • type: the type of cache storage

    • filename: the location of the cache

caches:
  aerial2013_cache:
    grids: [grid_gb]
    sources: ['aerial_wms_2013:aerial2013']
    cache:
      type: mbtiles
      filename: E:\Tiles\aerial2013.mbtiles
  aerial2018_cache:
    grids: [grid_gb]
    sources: ['aerial_wms_2018:aerial2018']
    cache:
      type: mbtiles
      filename: E:\Tiles\aerial2018.mbtiles

Sources

This section defines the source of the data to be displayed and cached.

The Sources section will contain one or more sources, of which a single layer can reference one or more. The first line of the source will be used in the sources section of the layer as a reference. Each source will also have:

  • type: the type of source being referenced

    • wms: for example a MapServer layer configured in Studio, or an external WMS

    • tile: for example an existing tilecache on an iShare server

  • grid: a reference to a grid definition elsewhere in the YAML file

  • url: the location for the tilecache or WMS

 sources:
  aerial_wms_2013:
    type: wms
    req:
      url: http://127.0.0.1/Mapserver/ms761?map=E:/iShareData/LIVE/_MapServerConfig/base_raster_aerial_2013.map
    http:
      ssl_no_cert_checks: true
  aerial_wms_2018:
    type: wms
    req:
      url: http://127.0.0.1/Mapserver/ms761?map=E:/iShareData/LIVE/_MapServerConfig/base_raster_aerial_2018.map
    http:
      ssl_no_cert_checks: true

Grids

This section contains details of the coordinate reference system used by the cache. The first line contains the referenced used by the caches section. Each grid contains:

  • origin: the origin point of the grid in relation to the grid area - the default is sw

  • srs: the coordinate reference system/spatial reference system being used by the data, using the EPSG code

  • bbox: the bounding box of the grid, i.e. the extent of the data, using the units specified in bbox_srs

  • bbox_srs: the SRS of the units specified in bbox

  • res: the resolutions that MapProxy will cache - see the section below on Adding Scales for more detail on this.

  grd_os_raster_road:
    origin: nw
    srs: 'EPSG:27700'
    bbox: [-238375.0,0.0,900000.0,1376256.0]
    bbox_srs: 'EPSG:27700'
    res: [896.0, 448.0, 224.0, 112.0, 56.0, 28.0, 14.0, 7.0, 3.5, 1.75]

Adding Scales

The default scales may not cover the range of scales you wish to provide for your basemap, and MapProxy can help with this. The cache upscale_tiles as described in the cache documentation can scale tiles up depending on your requirements.

chc_my_basemap:
  grids: [ "grd_my_basemap" ]
  sources: [ "src_my_basemap"]
  meta_buffer: 0
  minimize_meta_requests: true
  upscale_tiles: 1
  cache_rescaled_tiles: true

This lets MapProxy know that any tiles that cannot be retrieved from the source should be rescaled from the next level up. Please note that this will not happen if there is an error returned from the source, just if the source is limited on what resolutions it can return. Again, please read the documentation for more information.

sources:
  src_my_basemap:
    type: tile
    grid: grd_my_basemap
    url: https://mymaps.com/maps/raster/v1/wmts?height=256&width=256&style=default&layer=My_Basemap&version=1.0.0&service=WMTS&Request=GetTile&format=image/png&TileMatrixSet=EPSG:27700&TileMatrix=EPSG:27700:%(z)s&TileRow=%(y)s&TileCol=%(x)s
    max_res: 0.109375
    min_res: 896.0

We need to set a max_res and min_res in the source to specify what resolutions the source supports returning.

grd_my_basemap:
  origin: nw
  srs: 'EPSG:27700'
  bbox: [-238375.0,0.0,900000.0,1376256.0]
  bbox_srs: 'EPSG:27700'
  res: [896.0, 448.0, 224.0, 112.0, 56.0, 28.0, 14.0, 7.0, 3.5, 1.75, 0.875, 0.4375, 0.21875, 0.109375, 0.0546875, 0.02734375, 0.013671875, 0.0068359375]

The final step is to increase the number of resolutions that are available for the basemap so that the client will pick them up, just remember that any specific WMTS scale is the previous scale divided by two. In the example above, the following resolutions will be scaled as they are outside the source max/min res limits.

0.0546875, 0.02734375, 0.013671875, 0.0068359375
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