There you are, ambling north across Waterloo Bridge watching the left-hand side of Tower 42 (the former NatWest Tower) way off in the distance and keeping an eye on St Paul's Cathedral, some way to the left.
It's not actually you but a steadicam operator doing the walking, for this is the crucial Hayes Davidson's movie visualisation for the recent Heron Tower inquiry. By the time you hit the corner of Somerset House and the obscuring foliage of the Embankment trees, the Heron Tower has detached itself by the merest sliver of light from Tower 42, St Paul's dome is more or less the same distance away on the left and you are already grinning to yourself at dear old English Heritage's miscalculation.
It had claimed that the view of the cathedral dome from Waterloo Bridge is sacrosanct. But, you have just discovered, that is just as true with the Heron tower in place. This telling moving image is the work of Alan Davidson's company, Hayes Davidson. Already the best three-dimensional architectural visualiser in the business and, come to think of it, anywhere in the world, Davidson's company has claimed a new high ground. It is the new territory of verifiably accurate representations of both buildings and, as at the Heron inquiry, their environments.
Everyone at the inquiry was horrified at the amount of time spent on trying, unsuccessfully, to take apart the Hayes Davidson visualisation methodology, which is based on mainline surveying techniques.
Davidson is now arguing for a code of practice to minimise this kind of process in planning inquiries: 'I think the most professional thing we could do is to make both sides comfortable with the methodology - and get on with the serious debate, ' he says.
On the whole, he is pitted against the conservation lobby, mostly, he says, 'because our clients are people who want to build.
But we do talk to the conservation lobby, or we try to, as much as with developers.' And he is currently meeting with English Heritage on the agreed methodology issue.
Davidson's soft Aberdonian burr and courteously diffident, boyish, slightly selfdeprecating manner all briefly lull you into forgetting that a few millimetres under the surface is a steely persistence and a preoccupation with knowing exactly what is going on. He is occasionally accused of being overly secretive. In his business, confidentiality can be a critical issue. But it is true that he gives away little about himself.
It's not always appreciated, for example, that he is a registered architect. He read architecture at Edinburgh University first, recalls one of his contemporaries, as a civil engineer, then as a fine artist, before he settled into architecture. He was that rare thing, a bright Scot among the mainly English students at Edinburgh University.
He was computer-literate, already marked for great things. And he drew like a dream.
At the beginning of the 1980s he took a double year out to work with Stuart Huggett's Fiji practice, Architects Pacific, before returning to complete his MA. 'I learned so much, ' Davidson says. 'I did a lot of tropical swim bars and fire-walking arenas and became a dab hand at thatch details.' The work might have been conventional, but Stuart Huggett had a vision. 'He had bought four or five early pre-Mac Apple computers and the second time I was there he had bought the first Macs with MacPaint and a spreadsheet. I had been an adolescent Sinclair ZX81 programmer and in Fiji it was natural for me to get into using spreadsheets for analysing architectural problems.' Back in the, UK Davidson worked for ORMS and was inspired by the leading-edge Mac architectural nexus populated by people such as by Andrew Herron and Ben Banham.
Davidson says: 'I wasn't part of their circle, but I was fascinated with what they were doing. They were so passionate about the Mac. At that time the big advantage the Mac had was that it had Photoshop and Electric Image. Here was visionary software on a visionary machine.'
Davidson moved to the Richard Rogers office but scarcely two years after coming to London he set up Hayes Davidson, in 1989. Within a couple of years his team was winning awards - the CICA had to enlist Davidson as a judge because, embarrassingly, he had won its computer graphics award for the previous three years and looked like doing so forever more. By then the de rigeur three-dimensional visualiser for the British architectural illuminati, he moved his company, numbering around 30 staff, in under the high roof of what had been Peter Gabriel's music studio at the back of Paddington Tube station.
Davidson may have come into visualisation because of an enthralment with what the hardware and software could do. But the reason for his excellence in the field is because he deploys the eye of an artist, rather than that of an architectural renderer or watercolourist. He worries about how car tail lights can best be reflected on wet tarmac, how the shadows of the open door on a third floor will help to illuminate the depth of the space behind the windows, how the reflections of adjacent buildings help to model the irregular profile of a building's skin. Applied to computer imaging, this has been pioneering stuff. But his architectural background means there are more dimensions than even verifiable visualisation. One of these is his eCity, a three-dimensional digital model of London.
It's not the only one. But what Davidson does with it is probably unique. It is based on a very complex database/spreadsheet which enables him to run what-if analyses of the city based on a wide range of criteria, including price per square foot, area, height, rateable value and a lot more. You suddenly realise how utterly primitive is conventional planning. With eCity you can see immediately what the consequence of a building or planning proposition is.
Davidson says: 'All this other stuff we do is subsidised by our broader work. It's a shame there isn't a client for it.'
Maybe it says something about our planners that there isn't.