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T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 1 6




Clients are struggling to specify clearly

their 3D data needs and the supplier/client

relationship is faltering. Sometimes the

client strays into the supplier’s territory by

specifying the technology (‘I want a laser

scan’) rather than defining the product (‘I need

a 3D wire-frame model to this specification’).

And as an industry we are sometimes guilty

of promoting the technology rather than the


However, clients in the heritage sector

are almost unanimously enthusiastic about

the potential of 3D information, particularly

because of its ability to communicate complex

information to the public. Heritage sector

clients can be demanding, keen to have

a comprehensive record of their site and

wanting 3D digital models for visualisation,

digital reconstruction and augmented reality.

Budgets, however, are usually very limited and

it is the task of the specialist survey supplier

to attempt to meet their aspirations at a

cost that is affordable and, in some cases, to

provide early advice on the practicalities and

implications of various methodologies.

Often, for the comprehensive

documentation of a heritage site, other field

datasets are obtained and this can include

archaeological excavation information in

addition to geophysical, ecological and

condition surveys. Historical evidence may be

available in a wide variety of forms including

maps, plans, documents, reports, photographs,

etchings and paintings, and these are valuable

where digital reconstruction is wanted – for

example, to display a particular period in a

site’s history (Figures 1 and 2).


Today specialist surveyors can use a number

of measurement technologies to create survey

imagery and 3D datasets to meet clients’

needs. Each has particular applications and

each has its advantages and disadvantages (in

addition to cost implications).

Laser scanning

Laser scanning captures a large amount

of 3D data, generating the now familiar

‘point cloud’ where each point has a distinct

Cartesian location, light intensity and colour.

Scanning can be done in poor light and even

at night. Data can be captured rapidly but the

instruments are relatively expensive. Another

disadvantage is that laser scanners can have

difficulty in obtaining data at height. Most

laser scanners require a stable platform during

scanning and using hoists and scissor lifts

can prove troublesome. For these reasons it

rarely provides a complete point cloud over a

complex heritage site and even with careful

planning, data voids can be significant.

In the heritage sector the point cloud is

rarely the final deliverable and laser scanning

may be an expensive solution depending on

the client’s actual needs.

Photogrammetry and Structure


Although it has a long history,

photogrammetry remains a powerful

means of obtaining point cloud data.

Stereo photographs are taken with precise

measurements and calibrated to allow

accurate orthographic imaging. More recent

Structure from Motion (SfM) techniques

follow the same principle but use a large

number of images from fixed-wing aircraft

or unmanned aerial vehicles (UAVs) and/

or taken from cameras on the ground,

on platforms, or mounted on poles that

allow comprehensive coverage of a site.

The images are processed to create a 3D

point cloud, mesh and textured mesh at a

resolution to suit the final output or use.

Instrument survey

Traditional land survey techniques using

total stations and GPS equipment are often

used to provide the control framework for the

laser scan and photogrammetric data capture

processes and to supplement the point cloud

information captured by other methods.

Only the points selected in the field to

create the final output are measured. Figure 3

shows the vectors captured by a reflectorless

total station to define a building facade.

Subsequent modelling and photographic

texture were added to the model to create the

end-product. For a client viewing the end-

product, it would be difficult to determine the

mix of methodologies used, but each provides

distinct types of data which can be extracted

and used for a variety of functions.

Traditional measured survey

In spite of the advanced survey technologies

available, there are many situations where a

very low-tech approach is equally effective

for the survey of historic buildings and may

be more appropriate and cost-effective. This

is particularly true for smaller, more complex

or irregular structures, for the recording of

individual architectural details or for sites

where survey needs to take place in stages

– before and then during a programme of

building works.

It is a distinct advantage that survey is

carried out in detail by those who are also

responsible for assessing and understanding

the building, so analysis can be made

and developed as the survey proceeds in

a continuous and seamless process. Thus

the ability to carry out accurate hand

measurement and good drafting skills

developed over many years are essential tools

for many buildings archaeologists.

Hand survey can involve a spectrum

of activities – sketched individual details,

measured sketches, hand-measurement of

features which are then drawn directly onto

metric paper, the marking-up of existing

drawings or imagery, and so on. And most

commissioned survey work on historic

buildings, whether digital or by hand, still

involves a significant component of close

secondary scrutiny on site by the archaeologist

during which survey imagery is subject to

correction and refinement, and the layering-

on of detailed analytical and interpretive

information. There is little substitute for direct

one-to-one contact between archaeological

surveyors and their subjects.

Today the outputs of such drawn surveys

are usually converted into digital imagery in

the office and can then be merged with most

other digital graphics media.


None of these data capture techniques in

themselves generate the final output or

analytical record of a building. The imagery

requires processing, presentation to the

required standard and the addition of further

layers of interpretive information. High

quality survey data can obviously support and

speed up this process but it is only ever the

base for a full analytical visual inspection and

detailed record.

An archaeological analysis of a historic

building typically gathers a great deal of

additional qualitative information, usually

through a process of careful visual inspection

of the subject.

It is routine for this information to

be superimposed on the graphic imagery

as additional layers or linked information

(Figure 6). This includes constructional

information, material types, information

relating to phasing and function, catalogue

references for information on specific features,

mapping of mortar types, petrological

assessment and so on. There are also inputs

from other specialists such as moisture

mapping, rot surveys, the plotting of

structural failure and paint analysis data.

Figure 3 A 3d textured model created from total station survey measurements