Sources

As stated in the Structure Overview, the sources section is mandatory. This section always contains one source that describes data format provided by a provider. Currently, data can be provided on tile basis in two formats: GeoJSON and OMV - a format that follows Vector Tile Specification.

As an example, H.service.omv.Provider provides HERE Vector Tile Service data in OMV format, and H.service.traffic.flow.Provider provides HERE Traffic Flow Data in GeoJSON format.

A source section contains the following parameters:

• type - mandatory parameter that specifies the format provided by the provider. It can be either OMV or GeoJSONTileSource.
• extra_data - optional parameter that contains any additional data that will be passed to the transform function.
• transform - optional parameter that allows to process tile data right in the style. This can be either a function:

sources:
  omv:
    type: OMV
    transform: |
      function(data, extraData, tileInfo) {
        if (data.water) {
          for (let i = 0; i < data.water.features.length; i++) {
            data.water.features[i].properties.myProperty1 = 'myValue1';
          }
        }
        return data;
      }

or multiple functions that will sorted by their names and called in corresponding sequence:

sources:
  omv:
    type: OMV
    transform:
      f1: |
        function(data, extraData, tileInfo) {
          if (data.water) {
            for (let i = 0; i < data.water.features.length; i++) {
              data.water.features[i].properties.myProperty1 = 'myValue1';
            }
          }
          return data;
        }
      f2: |
        function(data, extraData, tileInfo) {
          if (data.water) {
            for (let i = 0; i < data.water.features.length; i++) {
              data.water.features[i].properties.myProperty2 = 'myValue2';
            }
          }
          return data;
        }

Each transform function accepts the following arguments:

1. data - object that contains data from the current tile. This object contains a list of layers (pois, roads, etc.), where each layer is a GeoJSON FeatureCollection. Some providers (for example, H.service.traffic.flow.Provider) provide only one GeoJSON FeatureCollection per tile, in such cases this GeoJSON FeatureCollection will be passed as a data instead list of layers.
2. extraData - content of the extra_data optional parameter defined in the source section.
3. tileInfo - object that contains information about the current tile, for example tile coordinates. Each transform function must return the modified version of the data parameter.