Parallax in Burrow Bridge

I had a brief exchange with commenter Tim on Bishophill earlier today. He was asking how the different perspectives of the photographs (1 and 2 below) might affect what we are looking at. It was a good question. I then began to look in more detail at the arrangement of buildings on the far bank and doubts entered my mind if this was the same bridge. With this image of the River Parret in Burrow Bridge, Somerset, set to become an iconic image for the floods and government complicity in bringing them about, it would be poor form if somehow the two photographs were of different bridges.

Figure 1 Image 1 dated to early 1960’s, image 2 is recent and image 3 very recent during current floods. Building B in images 1 and 3 looks the same, but in image 1 it appears to the right of the bridge and in image 3 it appears over the centre of the bridge. I realised this could likely be explained by parallax but could not figure out in my head how to align these views. So I had a quick look at Google Earth which provides the answer – below the fold. Original photo from Wattsupwiththat based on a comment originally posted on Bishophill.

This is how wikipedia defines parallax:

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight.

Figure 2 Google Earth image of Burrow Bridge. Imagery 6 Feb 2009. 1 and 2 shows the approximate positions of the two photographs. The red and blue lines are the lines of sight. Note how building B appears over the centre of the bridge from position 2 but to the right of the bridge from position 1 – the parallax effect. Click on image for large version.

Image 1 appears to be taken about 50 m away (upstream ?) from the bridge, probably with a telephoto lens whilst image 2 is taken perhaps 10 m from the bridge. Building A has 3 distinctive chimneys clearly visible on the GE image and on photographs 1 and 2 (Figure 1). From position 2 building A appears over the left centre of the bridge while from position 1 it appears over the right end of the bridge as seen in images 1 and 2.

Building B is not clearly visible in image 2 but is in image 3 where it appears over the centre of the bridge. In image 1 it appears to the right of the bridge. The GE image (Figure 2) shows how this comes about. The line of sight from position one clips the edge of the pub (building C) and places building B to the right of the bridge.

Looking at images 1 and 2 again you can see that the older image 1 is more square on to the bridge while image 2 is more oblique explained by the different photographic positions. Since the early 1960’s a pipe has been added to the bridge and building A has been painted white.


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4 Responses to Parallax in Burrow Bridge

  1. I never doubted they were the same bridge! Did you look on Street View from ‘Riverside’ on the other side of the bridge? That made me realise how little vegetation there is in Image 2. There, it looks as if it has recently had the channel dredged and the mud thrown up on the banks, thus raising them. Not that it does anything for the total capacity of the river; out of the bottom, but narrowing the width. The lushness of the vegetation in the Street View suggests even more constriction.

    Another factor to consider with parallax, is the focal length of the camera lens. Image 1 was probably taken with a 4 or 6″ lens; totally different result to today’s digital cameras, or even a 35mm camera.

    • Euan Mearns says:

      Tim, I realise your initial question had a different angle but normally I’m pretty good at rearranging geometric spatial distribution in my head and couldn’t quite do it this time. So this is a vanity exercise to compensate for my own inadequacies. Its possible there are 20 bridges that look like this in Sommerset, so just wanted to make sure. Street view didn’t work for me this time 🙁

      My gut feel is that Booker’s piece building on much splendid blogging – though I found out this evening he has been one of the principle leaders in this search for truth – may actually lead to some Green Heads rolling. So I thought it worthwhile pushing the boat out to secure the veracity of these images. E

    • It doesn't add up... says:

      I suspect that the 1960s picture was taken by a 35mm camera with a standard 50mm lens: the giveway is partly the format, and partly the angle of view. It is notable that the poplar trees on the river bank have since been felled. They would have helped stabilise the bank.

  2. Radical Rodent says:

    In Streetview, look at the bridge from Riverside, downstream of the photo points (close to building A); the hole in the bridge on the cameras’ bank is almost entirely blocked, while daylight is visible through it in the older photo. Merely looking at the river, it does appear significantly narrower than in the older photo.

    That the photos are of the same bridge can be of little doubt, considering the location and appearance of the buildings. I think to dispute this would require evidence against rather than a call for proof that it is.

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