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ActiveStorageで保存するJPEG画像のEXIFをmetaデータにしたい時

Last updated at Posted at 2019-08-25

やりたい事

YourModel.first.image.metadata # => {latitude: ..., longitude: ...}

デフォルトで入っているImageAnalyzerは画像のwidth、heightしかmetadataとして取ってくれない。
https://api.rubyonrails.org/classes/ActiveStorage/Analyzer/ImageAnalyzer.html

解決策

  • exifr/jpeg
  • timezone_finder

を使う。

まず、exifr/jpegでJPEG画像のEXIFを取り出し、GPS情報を取得。

  • latitude
  • longitude
  • gps_date_stamp
  • gps_time_stamp

gps_date_stamp、gps_time_stampはUTC。 https://www.exif.org/Exif2-2.PDF
95e82e537d78fc41bae5e6ea2ccde143.png
ed13c3b3394c498daee58c7122e16590.png

UTCの時間をなるべく正確な現地時間にするためにtimezone_finderを使う。

exif_jpeg_analyzer.rbなどとしてconfig/initializersに入れる
# 元ネタはここ
# https://www.georg-ledermann.de/blog/2018/05/15/exif-analyzer-for-active-storage/

require "timezone_finder"
require "exifr/jpeg"
class ExifJpegAnalyzer < ActiveStorage::Analyzer::ImageAnalyzer
  def metadata
    read_image do |image|
      if rotated_image?(image)
        { width: image.height, height: image.width }
      else
        { width: image.width, height: image.height }
      end.merge(gps_from_exif(image))
    end
  rescue LoadError
    logger.info "Skipping image analysis because the mini_magick gem isn't installed"
    {}
  end

  private

  def ref(gps_ref)
    %w[N E].include?(gps_ref) ? 1 : -1
  end

  def gps_from_exif(image)
    {}.tap do |hash|
      next unless image.type == "JPEG"
      next if image.is_a? ActiveStorage::Variant

      image_data = EXIFR::JPEG.new(image.path)
      if image_data.exif&.fields[:gps]
        latitude = image_data.gps_latitude.to_f * ref(image_data.gps_latitude_ref)
        longitude = image_data.gps_longitude.to_f * ref(image_data.gps_longitude_ref)
        time_zone = TimezoneFinder.create.timezone_at(lat: latitude, lng: longitude)
        date_time =
          "#{image_data.gps_date_stamp.split(":").join("-")} #{
            image_data.gps_time_stamp.collect(&:to_i).join(":")
          } UTC"
        hash[:latitude] = latitude
        hash[:longitude] = longitude
        hash[:altitude] = image_data.gps_altitude.to_f
        hash[:time_zone] = time_zone
        hash[:date_time] = date_time
      end
    end

  rescue EXIFR::MalformedImage, EXIFR::MalformedJPEG

  end
end

# https://api.rubyonrails.org/classes/ActiveStorage/Blob/Analyzable.html
Rails.application.config.active_storage
  .analyzers.delete ActiveStorage::Analyzer::ImageAnalyzer
Rails.application.config.active_storage.analyzers.append ExifJpegAnalyzer

これによりmetadataにGPS関連が入る。

YourModel.first.image.metadata 
# => {latitude: ..., longitude: ..., altitude: ..., time_zone: ..., date_time: ...}

# これで撮影時の現地時間が取れる
metadata = YourModel.first.image.metadata
Time.parse(metadata[:date_time]).in_time_zone(metadata[:time_zone])
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