Tommy Grønvold has repeated the measurement that Rory did.

Location: 59.058238, 10.407123

There is a straight edge set close to the horizon.  This controls any potential distortion due to lens distortion.  Here is the image scaled to 1920×1280, click for the full size:

You can download the original, unedited RAW image file directly from the camera: IMG_0688

I manually counted the pixels between the straight edge and the horizon at 100-pixel increments across the entire image.  These gaps were entered into a spreadsheet.  This was graphed and a second-order polynomial line fit was applied.  The line is clearly curved.

A screenshot of the pixel counting is on the right show here as an example, click on it to see a larger version.

You can also download the full photoshop file after all the pixels have been counted: IMG_0688.psd

Here is the Excel document with the results of the counted pixels: Tommy G gap measured

 

Photo info:

• The ship on the left is the Color Magic which is 225 meters long.
• The lens is a 10-20mm wide-angle lens, not a fisheye lens.