DETECTING CHANGES TO TOPOGRAPHIC FEATURES USING HIGH RESOLUTION 
IMAGERY 
D. A. Holland, C. Sanchez-Hemandez, C. Gladstone 3 
‘Research, Ordnance Survey, Romsey Road, Southampton, UK - 
(David.Holland, Carolina.Hemandez, Catherine.Gladstone)@ordnancesurvey.co.uk 
Commission VI, WG VI/4 
KEY WORDS: Change Detection, Digital Mapping Camera, Cartography 
ABSTRACT: 
Detecting changes to topographic features is one of the major tasks of a national mapping agency. At Ordnance Survey, Britain’s 
national mapping agency, the process of change detection has traditionally been a largely manual, labour-intensive task. One of the 
goals of the Research department is to develop automatic and semi-automatic change detection processes which could be developed 
into production systems. This paper describes the research undertaken, concentrating on the detection of changes to the built 
environment, specifically new and demolished buildings. The research has progressed from a set of potential methodologies; 
through research trials of different software packages and different change detection methods; to the adoption of one of the methods 
in a full production trial. 
1. INTRODUCTION 
1.1 Background 
of the image, hence missing out one comer of the image and 
therefore miss any changes in that comer. 
The detection of change is one of the most important aspects of 
the work of a mapping agency. In the case of Ordnance Survey, 
Britain’s national mapping agency, this is still largely a manual 
process, relying on the observations of photogrammetrists and 
field surveyors and the notifications provided by external 
bodies. In the field, a network of approximately 300 surveyors 
is engaged in the process of updating the national topographic 
database, used in the production of the flagship 
OS MasterMap® large scale topographic data product. Part of 
the field surveyor’s task is to note any changes to the natural or 
the built environment, in order to mark these changes for 
subsequent data capture. In addition to this, local authority 
planning departments provide information on planning 
applications which may affect buildings and other urban 
features. Major house builders inform Ordnance Survey of new 
developments, while a further source of intelligence on changes 
in the landscape is provided by a commercial survey 
organisation, which supplies information on changes which will 
affect Ordnance Survey’s products. 
The final source of changes is a group of image interpreters in 
the Photogrammetric Survey department, whose job is to 
scrutinise orthorectified digital aerial photography and mark up 
any changes. These changes are subsequently captured in 
stereo using digital photogrammetric workstations. In spite of 
all the other sources of information, this last phase uncovers 
many changes which have, up to that point, gone un-noticed. 
Manually scanning through the images is a laborious task, and 
one which requires concentration and a disciplined 
methodology. In an investigation carried out by the Ordnance 
Survey Research last year it was found that when scanning an 
image from top left to bottom right, constantly zooming in and 
out, it can be difficult to keep track of which areas of the image 
have already been looked at. In some cases, a tendency was 
found for the image interpreters to gradually migrate to one side 
1.2 Automating change detection 
In order to help the data collection process, automation of the 
workflow could be achieved at various points. Fully automatic 
feature capture has been a long-term goal of several ISPRS 
working groups, but it is unlikely to be completely realised in 
the near future. Semi-automation of the capture of topographic 
objects is a feasible option - especially in areas where many 
features are repeated (such as housing estates where every 
house is almost identical to its neighbour). In Great Britain, 
however, this is very seldom the case. The continuous nature of 
topographic data revision usually means that changes are very 
local in nature, often involving only one or two features within 
an area of many un-changed features. 
Automation of the change detection process is more feasible, 
especially if the system is only required to detect that a change 
has occurred, without having to identify exactly what that 
change is. In recent years there has been continued 
improvement to photogrammetric and image processing 
software and the hardware on which they run. This has enabled 
systems to become more automated, either by aiding the 
interactive data capture process or by performing a pre 
processing step on images before the human operator becomes 
involved. The nature of the workflow at Ordnance Survey 
lends itself to the latter process, in which an automated process 
would identify potential changes, then an operator would 
confirm or reject each change. It was envisaged that such a 
process would save a considerable amount of time in the data 
collection workflow. 
There has been much research in the last two decades on 
techniques to automatically detect changes between images 
taken on different dates. Such techniques can be of value, but 
often they highlight many changes which are of no interest - 
such as minor changes to vegetation, or changes due to the