Stan Zaslavsky

So what is barrel distortion relevant to providing 3D photomontages to act as visual impact evidence?

Barrel distortion is when straight lines in a photo appear to bulge or curve outward towards the edges, making objects look stretched or wider than they are in real life.

When a photo is taken with a wide angle (typically 18mm or lower) lens, some objects towards the edges of the image can appear stretched or compressed, making them look unnatural or distorted. You’ll notice that in the right-hand foreground of the photo above, the bridge appears stretched out far more because of the nature of the lens.

The diagram above roughly shows how lines bend as they get closer to the edges of the image.

All linework must appear in a correct perspective for the 3D photomontages to be accepted as visual impact evidence. Any time something looks a bit off, it raises unnecessary questions that may diminish the value of the work. Furthermore, if the angle of the lens is too wide, it can make it challenging to understand the shape and proportion of objects accurately.

Additionally, while some distortion can be corrected in post-processing, minimising it as much as possible during shooting is essential to ensure the best quality images.

We generally don’t recommend correcting the vertical lines in the photo-editing software as the VCAT practice note PNVCAT 2 asks explicitly to refrain from modifying the photos as much as possible.

Human Eye-Sight and 3D Photomontages

The human eye does not have a “lens width” as a camera lens does. Instead, the eye has a more complex structure that includes a transparent lens, which helps to focus light onto the retina.

The lens of the human eye is approximately 9.6 millimetres in diameter and has a focal length of about 22 millimetres. However, it’s important to note that the human eye is not a perfect optical instrument, and there can be variations in these measurements depending on factors such as age and individual variation.

Additionally, the human eye has a variable field of view depending on where we focus our attention, which is different from a fixed lens on a camera. The field of view of the human eye is approximately 120-130 degrees horizontally and about 160 degrees diagonally.

The challenge is that when urban planning witnesses require a particular view to show a broad context of the site – they ask for the photo to show as much context as possible and use a wide lens.  Our usual recommendation is to use a lens range of 18-24 mm as it reaches a compromise of showing a lot of context without too much barrel distortion around the outer edges.

Camera Tilt

When the camera is tilted, the scene’s vertical lines appear slanted, creating a sense of imbalance or distortion. This is because our brains are wired to interpret vertical lines as truly vertical, and any deviation from this expectation can be jarring or disorienting.

For example, in a photograph of a building taken with a tilted camera, the edges of the building may appear to be leaning inwards or outwards, making it look unstable or distorted. This effect is particularly noticeable in architectural photography, where the accurate representation of lines and angles is essential for conveying the design and structure of the building.

So there must be a good reason why the camera must be tilted upwards. In the photomontage above – it was essential, as the camera tripod was instructed to be placed close to the building to understand the immediate neighbouring context, and the proposed building was cutting through the photo. In a case like this – the angle of tilt must be documented in the Statement of Methodology that is included with the 3D photomontages to form visual impact evidence for the VCAT hearing.

In Summary

Two cameras (our eyes) create our perception of a natural scene by merging the overlapping photos versus the photograph created by a single camera and this is something that will never be resolved until VR or a similar capability is developed to help panel members view the scene in 3D.

So while we are representing a proposed view to be used as visual amenity evidence, at this stage, we can only really compare what is currently existing and how the scene may look when the proposed development is complete.

Ultimately even if there is minimal distortion in the photographs, the before and after representation of the proposed development is sufficient for the VCAT panel hearing to review and understand the impact.

Reach out if any questions on the above come up and to your development success,


Stan Zaslavsky

BEng(Mech) (Hons) / BTech(Industrial Design), LREA, VPELA

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