Visual Impact Assessment (VIA) of proposed developments.
It is easy to get lost in the technicalities, but if a scene you are familiar with does not "look right" when you see it in a photo-montage, then the montage is wrong. Typical criticisms include distant hills, headlands and islands appearing much smaller than they should. It is always best to compare montages on site with the real view so that you have a proper reference.
Visual Impact Assessment of a development is supposed to include the general public and consultees who are not trained landscape architects. As such, any photo-montages used to support planning applications and in Environmental Impact Assessments should be immediately accessible and comprehensible to a non-specialist audience. Yet frequently images have complicated, incomplete viewing instructions that are mostly ignored, and as a consequence, the visual impression may be misleading. For example, panoramas are sometimes presented on electronic displays (e.g. via websites) that are neither wide enough, nor have enough pixels, to show the scene correctly. Images for VIA are obviously useless if they are not perceived as being similar to the real scene.
Problems with visualisations
The industry "best practice" for still photo-montages followed by NBDL stemmed from the Scottish Natural Heritage (SNH) guidance of 2006 (see references below). The key points about this guidance are:
SNH 2006 guidance relies on a simple geometric rule. However, it has been known for decades that humans do not perceive objects in photographs in a purely geometric way. There is no depth to a photograph, so the brain has to interpret the flat pattern of shapes and colours to create the perception of a three-dimensional scene. Visual cues, such as familiar objects, atmospheric haze, a horizon, and changes in surface texture with distance help the brain to decide the scale. Distant objects in photographs are often perceived to be smaller than they would be in real life; those mountains in your holiday snaps look insignificant even though they looked big at the time.
To compensate for human perception, a photograph has to be adjusted. Many factors are involved, so it is best to rely on careful experimental research to establish standards. Such a study was undertaken by the University of Stirling, and their results were published in May 2012. The study recommended that images taken with a 75mm lens (on a 35mm camera) should be used for wind farm visualisations most of the time. This results in larger-scale images than current guidance requires, which will be no surprise to many people who knew instinctively that standard developer panoramas did not "look like" their familiar local views (and distortion is also a factor).
- It results in photographs that should be viewed from a particular distance in order to create an image in your eye that is the same size as the real scene's image would have been.
- For wide-field images (panoramas), the long, thin images should be curved onto the arc of a circle and viewed from the centre of the arc.
- The theory behind the SNH 2006 guidance only applies if you look with just one eye.
- Viewing distances are permitted to be as close as 300mm (e.g. as used by Eneco in the Feb 2012 exhibitions, and the printed A3 booklet of photomontages from the March 2013 exhibitions).
SNH 2006 guidance relies on a simple geometric rule. However, it has been known for decades that humans do not perceive objects in photographs in a purely geometric way. There is no depth to a photograph, so the brain has to interpret the flat pattern of shapes and colours to create the perception of a three-dimensional scene. Visual cues, such as familiar objects, atmospheric haze, a horizon, and changes in surface texture with distance help the brain to decide the scale. Distant objects in photographs are often perceived to be smaller than they would be in real life; those mountains in your holiday snaps look insignificant even though they looked big at the time.
To compensate for human perception, a photograph has to be adjusted. Many factors are involved, so it is best to rely on careful experimental research to establish standards. Such a study was undertaken by the University of Stirling, and their results were published in May 2012. The study recommended that images taken with a 75mm lens (on a 35mm camera) should be used for wind farm visualisations most of the time. This results in larger-scale images than current guidance requires, which will be no surprise to many people who knew instinctively that standard developer panoramas did not "look like" their familiar local views (and distortion is also a factor).
Recent Developments in Guidance
The Highland Council in Scotland has had much experience of wind farm developments and in 2010 it introduced its own visualisation standard. This required images containing the field of view of a 75mm lens on a 35mm camera, printed at 360x240mm. In May 2013, they re-issued their standard to increase the image size to 390x260mm. Our reference images have been scaled for this larger print size. These images are called "75mm single-frames" even though they are usually cropped from an image taken with a 50mm focal-length lens on a 35mm camera. In the 2013 standard, it is made clear that images showing the full field of view of a 50mm lens, or panoramas, are not representative of perceived scale and distance.
In May 2013, SNH issued a consultation draft revision to its guidance and finally, in July 2014, it issued new guidance which requires the use of 75mm single-frame images and medium-width panoramas spanning around 54 degrees horizontally and 18 degrees vertically printed at the same scale as the single-frames. Crucially, these new panoramas are designed to be hand held and viewed with both eyes at a comfortable arm's length. So, the new guidance supports what critics have been saying for years and it is regrettable that it has taken so long to agree new guidance at a time when many wind farms were going through planning. For Navitus Bay, it means that the public has been denied a fair chance of assessing the true visual impact for themselves. There are still concerns about the exclusive use of the 54 degree panoramas at exhibitions as this is an unproven format, whereas 75mm single-frames are a proven alternative, especially when the whole wind farm fits within their field of view.
Comparisons
For the curious, we have produced a comparison of the old SNH 2006 guidance and the new SNH 2014 guidance so that you can judge for yourselves which images look more representative.
If you created two panoramas showing a 54 degree field of view, one using the 2006 guidance, the other using the new, and mounted them flat on a wall to compare, you might be surprised to find relatively small differences between the two images. The "old" image would be only 760mm wide and appear to be compressed sideways compared with the 820mm wide "new" image because of projection distortion, but you might conclude that the differences between the "old" and the "new" are minor. This would be wrong, of course, because the images were never intended to be viewed that way. The "old" image should have been curved into an arc of 813mm radius, and you should have viewed it with one eye from the centre of that arc. The "new" image is intended to be viewed flat with both eyes, hand-held at a comfortable arm's length. So, it is impossible to do a valid simultaneous comparison of the images. If you assessed the images independently as they are supposed to be viewed, you would reach a very different conclusion.
Limitations
Even printed images following the new guidance are limited in at least two respects:
A 75mm single-frame image cannot show the whole of a large wind farm at once. The only way around this is the panning technique which we already use in our videos (and now endorsed in the SNH 2014 guidance for viewing wide-field static images on a PC), or multiple images. Therefore, wide-field panoramas are still useful for showing the landscape context and on-site assessment by professionals who need a quick reference for the position and extent of the windfarm, rather than how it would look.
If you are interested in these technical issues, have a look at the references below.
- There is no movement in a printed image, but movement is very important in human perception, and
- the contrast of a print is much lower than that of a real scene (by a factor of typically more than 100).
A 75mm single-frame image cannot show the whole of a large wind farm at once. The only way around this is the panning technique which we already use in our videos (and now endorsed in the SNH 2014 guidance for viewing wide-field static images on a PC), or multiple images. Therefore, wide-field panoramas are still useful for showing the landscape context and on-site assessment by professionals who need a quick reference for the position and extent of the windfarm, rather than how it would look.
If you are interested in these technical issues, have a look at the references below.
VIdeo Guidelines
The SNH guidance does not apply to videos, but if videos are to evoke the correct perception of a scene:
- They should use good photographic backgrounds so that proper visual cues for perception of scale are present. Purely computer-generated scenes may not do this.
- The scene should always be presented to the viewer at close to the "correct" apparent size, so that its scale is correctly perceived. This means that zooming in and out should be avoided, as the question would then arise, which scale is the right one?
- The field of view should never be wider than the number of pixels on the screen can support whilst faithfully reproducing most of the detail that the eye could see. In practice, for offshore windfarms where detail is important, this means not more than 31x18 degrees on a 1920x1080 monitor, and not more than 21x12 degrees on a 1280x720 monitor (and even then, the scene will not be fully resolved). More info here.
- If used, panning rates must be slow enough that motion blur does not destroy the perception of the development.
References
Scottish Natural Heritage "Visual representation of windfarms. Good practice guidance.", 29 March 2006. www.snh.gov.uk
Scottish Natural Heritage "Visual representation of windfarms. Version 2", July 2014. www.snh.gov.uk
The Landscape Institute "Photography and photomontage in landscape and visual impact assessment (advice note 01/11)", 2011.
Hunter P. D. and Livingstone D. F. "The effect of focal length on perception of scale and depth in landscape photographs. Implications for visualisation standards for wind energy developments", University of Stirling report, 17 May 2012. Copies available from the Highland Council, Scotland.
The Highland Council "Visualisation standards for wind energy developments", January 2010 www.highland.gov.uk.
The Highland Council "Visualisation standards for wind energy developments", May 2013 www.highland.gov.uk.
Scottish Natural Heritage "Visual representation of wind farms. Consultation draft May 2013." www.snh.gov.uk
Gregory R. L. "Eye and brain, the psychology of seeing", fifth edition. ISBN 978-0-19-852412-0 Oxford University Press 1998.
Macdonald A. "Windfarm Visualisation, Perspective or Perception?", ISBN 978-184995-053-4 Whittles Publishing, 2012.
Scottish Natural Heritage "Visual representation of windfarms. Version 2", July 2014. www.snh.gov.uk
The Landscape Institute "Photography and photomontage in landscape and visual impact assessment (advice note 01/11)", 2011.
Hunter P. D. and Livingstone D. F. "The effect of focal length on perception of scale and depth in landscape photographs. Implications for visualisation standards for wind energy developments", University of Stirling report, 17 May 2012. Copies available from the Highland Council, Scotland.
The Highland Council "Visualisation standards for wind energy developments", January 2010 www.highland.gov.uk.
The Highland Council "Visualisation standards for wind energy developments", May 2013 www.highland.gov.uk.
Scottish Natural Heritage "Visual representation of wind farms. Consultation draft May 2013." www.snh.gov.uk
Gregory R. L. "Eye and brain, the psychology of seeing", fifth edition. ISBN 978-0-19-852412-0 Oxford University Press 1998.
Macdonald A. "Windfarm Visualisation, Perspective or Perception?", ISBN 978-184995-053-4 Whittles Publishing, 2012.