Enhance parsing of format for ExternalGraphic (IconSymbolizer)

[dsuren1]

Feature Request

With respect to IconSymbolizer, the format for ExternalGraphic is obtained from the image, but there are some cases where the image url doesn't explicitly mentions the format (ex. https://master.demo.geonode.org/documents/1623/link). In this case even though the source is valid, the format is not obtained by the parser which poses a limitation.

Describe the solution you'd like
The IconSymbolizer should also allow user to specify the format or the parser should try to obtain the content-type of the image provided to obtain the format if missing.

Describe alternatives you've considered

• There could be a support to have a format property for IconSymbolizer in geostyler-style which would allow the user to specify one (Limits the guessing of the format)

{
  name: 'External Graphic',
  rules: [{
    name: '',
    symbolizers: [{
      kind: 'Icon',
      image: 'https://sample.test.com/testlogo',
      format: 'image/png'
      size: 10,
      rotate: 90
    }]
  }]
};

• Or alternatively, without modifying geostyler-style, other parsers and component, the image format could be obtained from the content-type when the image URL doesn't have format mentioned

[jansule]

Good point!

I would prefer to extend the geostyler-style IconSymbolizer directly.

@dsuren1 it would be awesome if you can create a PR for this

[KaiVolland]

Fixed via geostyler/geostyler-style#280