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An image problem

With the report due soon on the Heron Tower planning inquiry, we examine a landmark in digital presentation

Architects have long been known for their creativity in producing perspectives of proposed buildings. With the right viewpoint, a knowing eye and imaginative background painting, any competent perspective artist can transform architectural pigs' ears into decent, unassuming buildings worthy of planning permission.

The bad (or perhaps good) news is that the planners have got wise. It used to be impossible (until the building was completed) for them to pinpoint where the exaggeration or diminution in a perspective occurred. That is because, however precisely set up with straight lines on a drawing board a perspective might be, it is actually a sketch, a work of imagination which is all but impossible to deconstruct.

It took a while for it to dawn on anybody that the coming of computer-aided design involved the introduction of unwelcome precision.

Once a three-dimensional digital model of a building was set up there could be generated an infinite number of perspective views of it under different lighting conditions and from a variety of 'camera' views. Naturally the most favourable was picked. But if the architect could do that, so could the planners more easily demand a different view - which was perhaps more illuminating as to bulk and effect on surrounding buildings.

And that is exactly what happened at the Heron Bishopsgate Tower planning inquiry. To many it sounds like a matter of pressing a few keys and waiting for the new image to roll out.

In fact, it takes a lot of work and time to produce new images.

KPF designed the tower using Bentley MicroStation on a network of Windows 2000 PCs, some of them with dual processors. The most recent incarnation of the application, version 8, can read and write native AutoCAD files - which the British construction industry has more or less settled on as its CAD standard.

Lars Hesselgren, KPF's head of graphic imaging, says: 'We use MicroStation for all our design and modelling and rendering.' That is because the application does all these things seamlessly. It makes sense not to have to change graphic user interfaces and procedures just because you are changing from production drawings through three-dimensional models to rendering and even animation. And a MicroStation file can be rendered by a number of computers simultaneously on the office network - each allocated a horizontal band of the image. Hesselgren says: 'We did animations for Heron using 20MB files and managed to render 2,000 frames using 30 machines in the office in just two days.

MicroStation's ray tracing is the fastest in the business.

'We have configured MicroStation in a standard way. People protect their own files but there is no need for special user privileges - so that everybody can use it. Because there is no real difference between using 2D and 3D, it raises the way three-dimensional design is used in the office.'

But in the hands of lawyers, CAD drawings are not good enough. The issue of verifiable precision became a critical one which KPF and Hayes Davidson had to take seriously.

Verification probably started, says Alan Davidson, managing director of Hayes Davidson, at the Poultry inquiry when surveyor Roy Fenton verified the accuracy of images using acetate sheets on top of photographs.

Things have moved on since then.

Hesselgren says: 'One of the key things in addressing this was the fact that over the years we have built up a detailed digital model of the City which sits on the Ordnance Survey map of the area. We add to it every time we do a new building and it now extends into the West End. It is this that we used to calibrate the 140 or so photomontages and used as proof that we have shown the correct angles.'

The procedure was to position the 3D model of the tower in the 3D digital model of the City. The ground level was raised to the average human eye height. A digital light source was attached to the top of the digital St Paul's and all the other lights turned off. The ray trace of this light enabled Hesselgren to establish from where, in London, people could see the dome of St Paul's.He sent KPF people out in cars to check the accuracy of the model and, apart from trees blocking some views, the model was verified in real life.

Lawyers being lawyers, one check was, of course, insufficient. Hesselgren says: 'The Ordnance Survey people refuse to guarantee accuracy of more than a metre, although it's actually about a foot. So as a second check we used LIDAR, sideways radar scans carried out during regular plane flights over the City. These were compared with our model at University College London.

'Then there is a third check by a firm of specialist surveyors which uses an enhanced radio positioning system which allows you to establish a position in Cartesian space to an accuracy of something like 5mm. They put up target points on key locations such as Waterloo Bridge, St Paul's and the former Natwest Tower and calibrated our 3D model against this.

'So in the end we were pretty sure our model was correct, 'Hesselgren says wryly, conscious that this sounds exactly like the massive overkill that it was.

Hayes Davidson was commissioned by Heron to produce a number of high-resolution photomontages - partly because it is proficient at this kind of thing and partly, one suspects, to dispel the idea that all the images had been cooked up by the same people. Its chosen software is Studio Max, LightScape and QuickTime VR.

Hayes Davidson was also responsible for the video of what was reckoned to be a crucial five-minute walk across Waterloo Bridge. Objectors had said that a key specific argument against the tower was that it would obscure the view of St Paul's for people walking across the Thames two and a half kilometres away.

The video involved four 6,000frame sequences and was interactive so that buildings could be switched on and off. But in essence Hayes Davidson shot a continuous video of the walk across the bridge and composited images of the tower into this.

In the process it had to deal with issues of parallax, camera positions and lenses and developed a method of 'locking' rendered buildings into videos. Because of the lawyers' preoccupation with verification, producing the video seemed rather less arduous than preparing the 120-page document describing the methodology that provided evidence of the video's veracity. Davidson, who always plays things close to his chest, is cagey about the precise detail behind the verification. 'The inquiry spent a long time working through the document, ' he says. But it was convinced.

Are we likely to see quite this scale of visual information in future bigleague planning inquiries?

The consensus seems to be that, although everybody was deeply admiring of its quality and usefulness, everybody also hopes not. Especially those who would be paying the lawyers. The function of images is to provide a fair representation in the inquiry room of the reality in the street.With buildings as big as the Heron tower you cannot build mock-ups, so accurate images are essential. It would be a pity, though, if planning inquiries became bogged down in long arguments about the minute veracity of images - rather than what they have to say. The trouble is, the images are so great.

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