Curvature of the Earth.
Because the turbines are so tall, and because some of the viewpoints in our region are quite elevated, curvature of the Earth has only a limited effect on visibility. As an example, the Needles cliffs, when seen from Durlston Castle 26km away, are not hidden at all by the curvature of the Earth.
The diagram above shows the geometry for a turbine that is "over the horizon", and the (approximate) formulae that you need to compute the unknown quantities. As an example, if the observer's eye is h=2m above sea level (ASL), the turbine height is T=189m ASL and it is 19km away (L=19000m), then from the formulae d=5053m, H=15.2m and a=0.0091 radians, or 0.52 degrees. Note that even at this range, for an observer standing on the beach, only 8% of the turbine's height is shielded by the curvature of the Earth. If the observer were higher, the shielding would be even less.
Panoramas and distortion of the view.
NBDL's 2013 Community Consultation viewpoint visuals booklet and Eneco's 2012 photomontages, in accordance with the SNH 2006 guidance, were created with a "cylindrical" projection, which means that they must be mounted on a cylindrical surface to be displayed accurately. However, most people will view the images flat because there is no instruction to do otherwise. By doing this, the sides of the images look too small, and horizontal dimensions are compressed, so the windfarm appears to be narrower than it really is. This distortion also often causes straight lines in the foreground to appear strongly curved, and other parallel lines appear to converge. Professional landscape assessors are familiar with compensating for such distortions, but we don't think this large distortion helps the public to form an accurate impression. This distortion, plus problems with viewing distance and resolution, means that any attempt to reproduce the whole of a wide-field photomontage on a standard computer screen or A4 sheet of paper simply does not work. Our videos avoid almost all the distortion because the field of view is narrower. The diagram below illustrates the geometry.
The red line represents one of Eneco's images (from the book of photomontages at the Feb 2012 exhibitions) laid flat on a table. The observer's eye is correctly positioned at 300mm above the middle of the photo. The diagram shows that point A', at the edge of the photo, is 461mm away from the observer's eye, and 49.4 degrees off to one side. However, to be seen correctly, the photo should have been laid onto a cylindrical surface represented by the green curve. If it had been, point A' would have been at point A, only 300mm from the observer, but 66.8 degrees to the side. So objects away from the centre of the image appear progressively smaller than, and not as far to the side, as they should. In fact, the horizontal scale at the edge of this photomontage (laid flat), as seen by a central observer, is only 42% of life size.
These problems have been recognised and corrected in the new SNH 2014 guidance. Photo-montages have a narrower field of view and are printed in "planar" (rectilinear) projection rather than "cylindrical" projection, which avoids the above distortion when the images are viewed flat.
Even modern electronic displays have quite poor resolution. A camera may have 24 million pixels in its sensor, but screens often have less than 2 million pixels, so you cannot always show the whole of a photograph at full resolution. It is important to retain detail in an image of an offshore windfarm, so the field of view has to be restricted (see the example below). Our HD videos show a vertical field of 18 degrees, using 1080 pixels. To retain most of the detail that your eye could make out in real life, we would have to increase the number of vertical pixels to more than 1440, which would give you a fairer impression. But then the videos would be inaccessible to most of you with "normal" sized screens. Just be aware that in real life the windfarm would be clearer than it is in our videos. The same issues apply to still images, and that is why it is impossible to display the whole of a windfarm panorama with sufficient resolution on a normal PC or TV. You may have seen this attempted on other websites, but the turbines become so heavily pixellated, they just disappear. This is highly misleading, so we do not show any panoramas on this site.
An example of how resolution affects perception.
These images illustrate what goes wrong when you try to show too much of a view on an electronic display. The left image is a small area from one of our video frames. The right image shows the same turbine group, but at one third of the resolution. As you can see, the turbines are disappearing into a blur. We could show the whole windfarm at once if we used the lower resolution, but then you would not perceive the turbines properly, which defeats the object.
High quality printed images on smooth paper can achieve a higher resolution than most electronic displays. A very good A3 print is equivalent (in resolution) to an electronic display of over 10 million pixels. In this sense, prints can be better than images on screens, but you cannot animate a print, and their contrast is poor, so the perceived resolution depends very much on subject and lighting.