Writing this ‘birthday memory’ for Irwin made me realise that I’ve known him for more than half my life – a life that is some 15 years shorter than his own.  However…  In 1974, the Council for British Archaeology held what it called a ‘symposium’ that was later published as Aerial reconnaissance for archaeology edited by David Wilson.  In this, Irwin had a contribution about transformation of oblique aerial photographs that included a computer method that accurately converted a point from an image into its x, y and z coordinate values.  Transformation of single points is fine if your case study is a group of Roman camps, as Irwin’s was, but a couple of years later I began a research project which would have as its root a map of archaeological features in 4000 sq km of Wessex.  My sites were wiggly things and I needed a means of transforming those with reasonable accuracy to 1:10560 maps.  I wrote to Irwin, or Dr Scollar as he then was to me as a mere student, to ask if he thought this would be possible and we began a discussion of appropriate mathematical methods.  At the same time, I was talking over the possibilities with people in the Computer Lab, Engineering and Scott Polar here at Cambridge.  As Irwin would say, ‘to make a long story longer’, I eventually succeeded in writing a computer program that enabled me to transform sites in my area.  I sent him a copy of the code and there followed an invitation to his laboratory in Bonn where I spent a month in December 1977 and ended up with a more-elegant version of my program thanks to Bernd Weidner, Irwin’s assistant at that time.  After a little more correspondence, with Irwin urging me to follow various mathematical ideas and me wanting to get on with my archaeological project, we lost contact for 20 years.

Early in 1998, Otto Braasch told me that Irwin was writing a program for transformation of oblique aerial images and I contacted him asking to be a beta tester, an offer he gladly accepted.  There followed many hundred emails that, we both agree, eventually made his AirPhoto 3 a good and effective program.  I used AirPhoto variants in my commercial work and for research, and it became the program that was taught in the many workshops in Europe that were organised on behalf of AARG.  AirPhoto was good in those contexts because output could be set to the local grid – a grid sometimes added by Irwin to the program a few days before the workshop.  One case of such was a Polish grid that comprised five unequal portions and I know was a challenge for Irwin to program.  Anyway, the Polish grid system was added in time for our workshop in Poznań and I suggested that we teachers should get Irwin a thank you present that I could deliver a week later when I was going to visit him.

At his request, we bought a Krakov sausage.  It was of generous size, perhaps 20cm long by 5cm in diameter, which travelled back to Cambridge in my hold luggage along with some of its relatives.  A week later, I set off to Stansted taking just a small backpack with the sausage packed near the top as I thought it may be something unexpected by the security people.  Sure enough, I watched my bag go through the x-ray scanner once, then twice, after which a bloke called me over.  Unzipping my bag, he said there seemed to be a bottle of water in it, then he pulled out the offending item.  “Oh, it’s just a sausage”, he said and put it back.  I’m good at saying the wrong thing at the wrong time but for once I kept quiet while thinking to myself ‘plastic explosive?’  The sausage was duly delivered with our thanks for the Polish grid system.  Maria let him have a slice but is very strict about their diet and I wondered if the rest was consigned to the bin.  But the thought was there as are my best wishes to Irwin on his 90th birthday.  When things have calmed down after those celebrations, I look forward to continuing our occasional Skype chats.