Download read more (PDF, 2335.63 KB)

VOLUME 4 ISSUE 8
NOV/DEC 2014
SCANNING THE
BLACK
DRAGON
20
HOSTING LIDAR DATASETS
32
ALL ABOUT THE SOFTWARE
40
WORKFLOW BEST PRACTICE
Reviewing a number of software products
& sites that host 2D & 3D LIDAR datasets
A detailed review of a novel handheld
imaging device reveals core necessity
Top 10 recommendations for the LIDAR
data workflow, from myths to utilization
Laser Scanning
of Threatened
Vernacular
Architecture in
South Africa
V
ernacular architecture is any
localized architectural style
addressing local building
needs through the use of local materials.
It is often in direct response to the
local environment. An important part
of every country’s unique heritage,
it should be preserved for future
generations. Unfortunately natural and
human-induced threats are causing
the loss of many vernacular sites in
South Africa. The African Conservation
Trust (ACT) in partnership with the
University of KwaZulu-Natal (UKZN)
have been using 3D laser scanning
BY MICHELLE DYE
technology to create permanent digital
records of South Africa’s threatened
vernacular architecture. Laser scan
data is used to isolate building weaknesses, take accurate measurements
to determine severity of damage, and
create detailed cross sections to assess
structural integrity. This information
can be used to assist land owners and
heritage management authorities in the
preservation of heritage sites.
Corbelled houses
The corbelled houses in South Africa’s
Northern Cape Province are the earliest
examples of vernacular architecture in
South Africa. The unique structures
were built by the early Dutch settlers
who arrived in the harsh semi-desert
landscape from about 1820. The settlers
found that within this landscape trees
were sparse but stones were aplenty.
To adapt, they made use of an ancient
method of construction known as
corbelling. In corbelled architecture successive courses of flat stone are placed
atop one another, with each row moving
further inwards until they almost met at
the apex. A single, larger slab is used to
cover the remaining hole.
Examples of corbelling can be found
across Mediterranean Europe; and the
corbelled Trulli Houses of Arabello,
Italy have been inscribed as a UNESCO
World Heritage Site. The corbelled
houses in the Northern Cape are the only
Displayed with permission • LiDAR News Magazine • Vol. 4 No. 8 • Copyright 2014 Spatial Media • www.lidarnews.com
Figure 1: Laser scanning a corbelled
house in the Karoo, South Africa.
Photo by Michelle Dye
known examples in Southern Africa.
Approximately 136 of these South African
houses remain. The structures represent a
unique phase in South African vernacular
architecture, yet many of the buildings
have been lost as a result of neglect,
damage from use as shepherds’ housing
or livestock enclosures, theft of building
materials, earth tremors, and modern
resource extraction.
Hydraulic fracturing (fracking)
applications are underway in the
Northern Cape and the corbelled houses
fall directly within the proposed fracking
area. Earth tremors have already caused
the collapse of several corbelled buildings and it is expected that additional
tremors from fracking in close proximity
will cause serious damage to the sites.
The buildings are also threatened by
modernization and loss of traditional
knowledge. The art of corbelling is no
longer practiced and as such many
land owners are stabilising the houses
with modern building materials and
techniques. Buildings have been patched
with cement or in some cases entire
walls have been plastered to stabilize
the structure. These non-traditional
modifications are not approved by
preservationists but with a lack of
funding support by heritage authorities,
land owners are resorting to changing
the vernacular nature of the buildings
rather than leaving them to collapse.
In order to digitally preserve the
vernacular styles of the heritage sites,
nine corbelled houses representing a
range of styles and conditions were
Displayed with permission • LiDAR News Magazine • Vol. 4 No. 8 • Copyright 2014 Spatial Media • www.lidarnews.com
Figure 2: Cross section of a corbelled
house showing how one side is bulging up
to 60cm, causing strain on the structure,
including the displacement of the structurally
significant door frame.
scanned. Data was collected with a Leica
ScanStation C10 and a Z+F Imager
5010C. The corbelled houses project
is additionally part of the larger CyArk
500 Challenge, which aims to digitally
preserve 500 significant and/or at-risk
cultural heritage sites around the world
within 5 years. The scan data of the
corbelled houses was used to assess
damage to the structures.
Figure 2 shows a cross section of a
corbelled house in very poor condition.
Large cracks are visible on the outside
of the house. Using the scan data, it
was possible to show that the building
is bulging by 60cm on one side. The
bulging has put considerable strain
on the walls and caused the structural
cracks. The scan data also revealed
that this shift in the walls has caused
the wooden door frame to pull 15cm
away from the building. As a result,
the door frame is offering no support
to the failing structure. Without any
stabilizing reinforcements, this building
is likely to collapse in time. Many of the
already-collapsed corbelled houses in
the Northern Cape have been lost due to
similar unaddressed conditions.
Zaaylager Voortrekker
Homestead
Built in 1853, the Zaaylager homestead
is one of the oldest Voortrekker
(early Dutch settler) houses in South
Africa’s KwaZulu-Natal Province. The
Figure 3: The main Zaaylager homestead and the carriage house in 2010. The chimney of
the kitchen can be seen behind the main house.
Photo by Celeste Rossouw
homestead is a rare example in which
the outbuildings are still in existence
(though they are in a poor state). On
most historic Voortrekker farms, only
the main house remains extant and the
outbuildings such as the milk room,
store room, carriage house and kitchen
have long been destroyed, mostly due
to neglect. The Zaaylager farm is also
the location of the first battle where
the Voortrekkers successfully defended
their position against the Zulus and is
associated with important Voortrekker
leaders such as Gert Maritz. Although
the building has been declared a
National Heritage Site in South Africa, it
has suffered from many years of neglect.
The farm is also bordered by a quarry
mine. Subsequent vibrations resulting
from the mine blasting have caused
damage to the structures. Despite the
significance of the homestead, the
mining has been allowed to continue.
The homestead’s foundations are also
sinking, which is putting additional
strain on the structure. As a result,
Displayed with permission • LiDAR News Magazine • Vol. 4 No. 8 • Copyright 2014 Spatial Media • www.lidarnews.com
Figure 4 (Right): Scanning
Zaaylager in 2014. The
deterioration is evident with
major cracking and wall
displacement visible. Beams
have been placed to support
the wall and prevent/delay loss
through catastrophic collapse.
Photo by Michelle Dye
Figure 5 (Left): Scan data of the Zaaylager
homestead showing the leaning wall with
support beams. At the right a zoomed view
shows measurements of the cracks spanning
up to 5.1cm. At the bottom is a cross section
of the leaning wall, showing the wall is
protruding to nearly 8cm.
water now collects around sections of
the house, exacerbating the problems.
Figure 3 shows the main homestead
and the carriage house as it was in 2010.
Figure 4 was taken in 2014 and the rapid
deterioration of the structure is evident.
Some of the outbuilding walls have
collapsed and one side of the main house
is being held up with support beams to
prevent/delay catastrophic loss of this
significant piece of South African heritage.
The Zaaylager homestead was scanned
using the Leica ScanStation C10 scanner.
The final dataset consisted of 18 individual scans and a total of 170 million points,
registered in Leica’s Cyclone software. The
laser scan data offers an accurate digital
record of this architecturally significant
homestead which is already in a dire state.
The scan data and processing software
were used to assess the structural damage
of the building. The reinforced wall was
analyzed to determine the extent of its
lean and the span of the major cracks
(Figure 5). This information is crucial to
establish whether the current beams can
adequately retain the wall or if further
support is required.
Conclusion
Vernacular architecture in South Africa
faces numerous threats and many sites
are highly degraded. Additionally, with
ever-increasing demands on resources
to support global population growth,
organizations such as UNESCO are
pushing for the study and re-instatement
of traditional (vernacular) architectural
practices. It is believed that vernacular
architectural methods, having evolved
directly from local conditions, are more
sustainable and should at minimum be
used to inform sustainable contemporary architecture.
3D laser scanning and other digital
preservation methods are providing the
tools to assess threats and damage to
these structures. That information can
be analysed to inform management and
restoration plans, or to educate architects
on sustainable construction techniques.
In cases where there is a lack of resources
to complete restoration, laser scanning
provides a lasting digital record to serve
as an accurate model for architectural
research and cultural posterity.
Michelle Dye is a member of the Heritage
Documentation Unit, a partnership between
the African Conservation Trust and
University of KwaZulu-Natal in South Africa.
Dye’s background is in geography. She
manages GIS and data processing for the
African Conservation Trust, where she has
been utilizing laser scanning since 2012.
For more information contact michelle@
projectafrica.com or www.projectafrica.com.
Displayed with permission • LiDAR News Magazine • Vol. 4 No. 8 • Copyright 2014 Spatial Media • www.lidarnews.com