RICHARDIII
80 JANUARY2021|COMPUTERSHOPPER|ISSUE395
Old maps showing the location of Greyfriars were available,
but very fewofthe landmarks on them are visible today,
which made it hard to locatethe siteprecisely.Today’s maps,
however,are incredibly accuratewhen it comes to existing
structures but don’t have the former church marked on
them. The solution involved atechnique called map regression
analysis, and while it’s not aparticularly computer-intensive
task, the story wouldn’t be completewithout mentioning this
essential first step.
Mathew Morris of the University of Leicester Archaeological
Services explains that they’d obtained aseriesofmaps dating
from the 17th century to the current day, andthatthe map
regression analysis involved comparing maps drawn at different
dates to understand the changes over time.
“Of these,one in particular,Thomas Robert’s map of 1741,was
extremely useful,”hesays. “It’s the earliest surviving map to show
accuratedetail of the area and it still clearly marks the ‘Gray
Fryers’ precinct.”Using aCAD program the team were able to
scale and orientatethis map to match modern Ordnance Survey
plans. Then, by identifying landmarks on the old map that still
exist today, such as roads, buildings and property boundaries,
theywere able to overlaythe two with areasonably high degree
of accuracy.This allowed them to outline aspecific search area.
The archaeologists could see that much of the area is now
covered with modern redevelopment, but there were still open
areas that appeared to have remained largely undisturbed since
the friary was demolished in the 16th century,which offered
cause forhope.Fortunately,these open areas echoed Philippa
Langley’s earlier research, and the likely location of Greyfriars
appeared to be one such open space –the now famous car park.
GOING UNDERGROUND
As fans of Channel 4’sTime Teamwill know,archaeologists are
often able to get aglimpse of what lies beneath the earth’s
surface.The various methods of geophysical surveying, or
‘Geophys’ as presenter Tony Robinson calls them, indicate
what might be hidden underfoot and where it would be most
profitable to start digging.
The options are limited in acar park because the hard surface
prevents physical contact with the soil, which is required foran
electrical resistivity survey, forexample.Instead, Philippa Langley
and the Richard III Society chose to probe the Leicester car park
with ground penetrating radar (GPR). Here,apulsed radio signal
is transmitted intothe earth and the echoes are monitored as the
equipment is wheeled across the surface.The time echoes take
to return provides information on the depth of anomalies in the
earth along the line of travel.
Youmight think the team would end up with adisplay
showing avertical slice through the ground, but it’s not that
simple.For astart, the radio signal spreads out in the ground, so
objects are detected even when the GPR equipment isn’t directly
above them. Signals take longer to return along these diagonal
paths too, which makes these objects appear deeper than they
are,soeven asingle point appears as an inverted hyperbola on a
display. When you consider that there maybeseveral artefacts,
⬆Map regression analysis allowed archaeologists topinpoint
the location ofGreyfriars
⬆SUMO Stratascan’s Claire
Graham shows the raw data
obtained from aGPR scan of
the Leicester car park Reproduced with kind permission of Philippa Langley
Whenconvertedintoa3Dimage
ofthe sub-surface,GPR data
suggested likely places todig
