private async Task initCamera(CameraSensorLocation sensorLocation)
{
Windows.Foundation.Size res = new Windows.Foundation.Size(MediaElementWidth, MediaElementHeight);
CameraOff();
camera = await AudioVideoCaptureDevice.OpenForVideoOnlyAsync(sensorLocation, res);
await camera.SetPreviewResolutionAsync(res);
frameBitmap = new WriteableBitmap((int)camera.PreviewResolution.Width,
(int)camera.PreviewResolution.Height);
}