In the middle of the Museum of London, confidently taking centre stage, stands a masterpiece. One of the Museum’s most admired, lingered over, talked about and valuable treasures is not a Roman coin hoard, a Saxon broach or a bejewelled medieval chalice. No, the jewel in both the Museum’s and the City of London’s crown is a vehicle, albeit a remarkable one. Built in 1757 at a cost of £860 (over £100,000 by modern standards), the Lord Mayor’s State Coach is now priceless. It is not possible to put a value on the Coach because it is one of a kind and has no comparison on the market; but it is clearly extremely valuable as it cannot be truly replaced. However, should it ever become necessary to reproduce it, it is estimated that to construct a facsimile would cost of the order of £2 million.

However, no original design drawings or subsequent working drawings exist for the Coach; mainly due to the incredibly elaborate and ornate nature of Coach that makes traditional measurement and survey almost impossible. Therefore the search has been on for a number of years for a suitable methodology to record the current form of the Coach and ultimately to legislate for any future proactive or reactive repairs that become necessary. We at Plowman Craven 3D, with our wide-ranging heritage and survey expertise and state-of–the-art technology, were approached by the Corporation of London to provide the answer to this survey conundrum.

The Lord Mayor's Coach is made up of a whole series of irregular components without obvious edges and flat surfaces. Traditional survey techniques, ranging from hand measurement, through measurement with electronic optical instruments such as total stations, to image based survey techniques such as photogrammetry, rely upon the identification and representation of edges. Because the Lord Mayor's Coach is made up of a number of irregular surfaces, a surface survey technique had to be employed to fully record the structure. For this laser scanning is the optimum recording system. LIDAR or terrestrial laser scanners have a resolution of +/- 5mm and whilst this was adequate to record the bulk geometry of the coach, it was too coarse in resolution to enable the full intricacies to be detailed. Therefore we chose to use our sub-millimetrically accurate close range scanning system, utilizing a laser triangulation system that is accurate to between 20 and 30 microns, to provide the high accuracy data.