Adds GPS metadata to an existing image file without re-encoding or re-compressing the image. Swift, iOS.

LocationMetadata.swift

import AVFoundation
import CoreLocation
import OSLog

private let logger = Logger(subsystem: "utilities", category: "images")

/// Adds the GPS metadata from `location` to the image file at `url` without re-encoding the image.
/// - Note: The image at `url` must be `JPG` or `HEIC` format. `HEIF` will not work.
/// - Warning: The file at `url` will be overwritten with a new file containing the updated metadata.
/// - Parameters:
///   - url: The location of the image file on disk.
///   - location: A `CLLocation` object whose information is to be added to the image at `url`.
func addLocationMetadata(to url: URL, location: CLLocation) {
    guard let source = CGImageSourceCreateWithURL(url as CFURL, nil) else {
        logger.error("\(#fileID) \(#function): Error creating source")
        return
    }
    guard let uti: CFString = CGImageSourceGetType(source), let fileType = UTType(uti as String) else {
        logger.error("\(#fileID) \(#function): Error getting file type")
        return
    }
    let tempURL = URL.temporary.appending(path: UUID().uuidString).appendingPathExtension(for: fileType)
    guard let destination = CGImageDestinationCreateWithURL(tempURL as CFURL, uti as CFString, 1, nil) else {
        logger.error("\(#fileID) \(#function): Error creating destination")
        return
    }
    var newMetadata: CGMutableImageMetadata
    if let imageMetadata = CGImageSourceCopyMetadataAtIndex(source, 0, nil) {
        newMetadata = CGImageMetadataCreateMutableCopy(imageMetadata) ?? CGImageMetadataCreateMutable()
    } else {
        newMetadata = CGImageMetadataCreateMutable()
    }
    let gpsMetadata = location.exifMetadata()
    for (key, value) in gpsMetadata {
        let success = CGImageMetadataSetValueMatchingImageProperty(newMetadata, kCGImagePropertyGPSDictionary, key, value as! NSObject)
        logger.log("\(#fileID) \(#function) set: \(key): \(success)")
    }
    let options = [
         kCGImageDestinationMetadata as String : newMetadata
         ] as [String : Any]
    var err: Unmanaged<CFError>?
    guard CGImageDestinationCopyImageSource(destination, source, options as CFDictionary, &err) else {
        logger.error("\(#fileID) \(#function): Failed to write metadata")
        print(err ?? "none")
        return
    }
    var fileError: NSError?
    NSFileCoordinator().coordinate(writingItemAt: url, options: .forReplacing, error: &fileError,
                                   byAccessor: { (newURL: URL) -> Void in
        do {
            try FileManager.default.removeItem(at: url)
            try FileManager.default.moveItem(at: tempURL, to: url)
        } catch {
            logger.error("\(#function): Failed to save attachment data to \(url)")
        }
    })
    if let nsError = fileError {
        print("###\(#function): \(nsError.localizedDescription)")
    }
    try? FileManager.default.removeItem(at: tempURL)
}

extension CLLocation {
    /// Returns a dictionary of GPS metadata values suitable for writing into an image file.
    func exifMetadata() -> [CFString:Any] {
        var gpsMetadata: [CFString:Any] = [:]
        let altitudeRef = Int(altitude < 0.0 ? 1 : 0)
        let latitudeRef = coordinate.latitude < 0.0 ? "S" : "N"
        let longitudeRef = coordinate.longitude < 0.0 ? "W" : "E"

        gpsMetadata[kCGImagePropertyGPSLatitude] = abs(coordinate.latitude)
        gpsMetadata[kCGImagePropertyGPSLongitude] = abs(coordinate.longitude)
        gpsMetadata[kCGImagePropertyGPSLatitudeRef] = latitudeRef
        gpsMetadata[kCGImagePropertyGPSLongitudeRef] = longitudeRef
        gpsMetadata[kCGImagePropertyGPSAltitude] = Int(abs(altitude))
        gpsMetadata[kCGImagePropertyGPSAltitudeRef] = altitudeRef
        gpsMetadata[kCGImagePropertyGPSHPositioningError] = horizontalAccuracy
        gpsMetadata[kCGImagePropertyGPSImgDirection] = course
        gpsMetadata[kCGImagePropertyGPSImgDirectionRef] = "T"
        gpsMetadata[kCGImagePropertyGPSSpeed] = speed
        gpsMetadata[kCGImagePropertyGPSSpeedRef] = "K"
        return gpsMetadata
    }
}