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Photo Location

The API can look up a human-readable location (city/state) from a photo's GPS metadata using Google Maps Geocoding API.

This feature is disabled by default.

Enable geolocation

{
  "ThirdPartyServices": {
    "EnableGeolocation": true
  },
  "GoogleMapsOptions": {
    "ApiKey": "<<GOOGLE_MAPS_API_KEY>>",
    "EnableMocks": true
  }
}

Notes:

  • GoogleMapsOptions.ApiKey is required by validation even if geolocation is disabled. Use any non-empty value for local dev.
  • EnableMocks only applies in Debug builds.

To get an API key, visit https://developers.google.com/maps/documentation/geocoding/get-api-key.

Google offers a very generous free tier for this service in the Pay-as-you-go plan. 10,000 free Billable Events per month. Unless you are refreshing the slideshow feed multiple times a day, for the entire month and every single photo contains GPS metadata, the fee quota is more than enough. https://developers.google.com/maps/billing-and-pricing/pricing

When the API calls Google

The Geocoding API is called only if all of these are true:

  • Geolocation is enabled
  • The photo has GPS metadata
  • The GPS metadata can be converted to decimal latitude/longitude

Otherwise, location is returned as an empty string.

Mocks

In Debug builds, if EnableMocks is true, the API returns (Mock)Nashville, TN and does not call Google.

Mocks are not wired in Release builds.

To disable mocks and make the call to the Geocoding API, given you have provided a valid Google Maps API key, set GoogleMapsOptions.EnableMocks to false.

Caching

Geocoding responses are cached for 10 days using .NET HybridCache:

  • L1 (memory) is always used.
  • L2 (distributed) is used only when Redis is enabled.

The L1 cache clears upon restart of the API. The L2 cache is persisted across restarts of the API.

The cache key is the concatenated latitude/longitude string: 36.130944444444445-86.76345555555555.

The way it works is HybridCache checks the L1 cache first, if it is a cache miss, it will check the L2 cache next. If this is also a cache miss, it will call the Geocoding API and store the response in both cache implementations.

I have configured Redis as the L2 cache. Refer to Redis for more details.